The Experts below are selected from a list of 540 Experts worldwide ranked by ideXlab platform

Brett A. Neilan - One of the best experts on this subject based on the ideXlab platform.

  • molecular and morphological survey of saxitoxin producing cyanobacterium dolichospermum circinale Anabaena circinalis isolated from geographically distinct regions of australia
    Toxicon, 2017
    Co-Authors: Joao P A Pereyra, Brett A. Neilan, Paul M Dagostino, Ian Jameson, Rabia Mazmouz, Jason N Woodhouse, Russell Pickford
    Abstract:

    Abstract The cyanobacterium Dolichospermum circinale (formerly Anabaena circinalis) is responsible for neurotoxic saxitoxin-producing blooms in Australia. Previous studies have reported distinct isolates of toxic D. circinale producing different saxitoxin analogues at varying amounts, but the mechanisms responsible remain poorly understood. To assess the characteristics that may be responsible for this variance, a morphological, molecular and chemical survey of 28 Anabaena isolates was conducted. Morphological characteristics, presence or absence of saxitoxin biosynthetic genes and toxin amount and profile were assessed. The 28 isolates were collected from 16 locations. A correlation between the size of the isolates and its reported toxicity or geographical location could not be found. Molecular screening for the presence of several sxt genes revealed eight out of the 28 strains harboured the sxt gene cluster and all tailoring genes except sxtX. Furthermore, the presence of PSTs was correlated with the presence of the sxt cluster using quantitative pre-column oxidation high performance liquid chromatography with fluorescence detection (HPLC-FLD) and LC-MS/MS. Interestingly, isolates differed in the amount and type of toxins produced, with the eight toxic strains containing the core and tailoring biosynthetic genes while non-toxic strains were devoid of these genes. Moreover, the presence of sxt tailoring genes in toxic strains correlated with the biosynthesis of analogues. A greater understanding of toxin profile/quantity from distinct sites around Australia will aid the management of these at-risk areas and provide information on the molecular control or physiological characteristics responsible for toxin production.

  • elevated na and ph influence the production and transport of saxitoxin in the cyanobacteria Anabaena circinalis awqc131c and cylindrospermopsis raciborskii t3
    Environmental Microbiology, 2016
    Co-Authors: Sarah E Ongley, Jasper J L Pengelly, Brett A. Neilan
    Abstract:

    Saxitoxins (STX), neurotoxic alkaloids, fall under the umbrella of paralytic shellfish toxins produced by marine dinoflagellates and freshwater cyanobacteria. The genes responsible for the production of STX have been proposed, but factors that influence their expression and induce toxin efflux remain unclear. Here we characterize the putative STX NorM-like MATE transporters SxtF and SxtM. Complementation of the antibiotic-sensitive strain Escherichia coli KAM32 with these transporters decreased fluoroquinolone sensitivity, indicating that while becoming evolutionary specialized for STX transport these transporters retain relaxed specificity typical of this class. The transcriptional response of STX biosynthesis (sxtA) along with that of the STX transporters (sxtM and sxtF from Cylindrospermopsis raciborskii T3, and sxtM from Anabaena circinalis AWQC131C) were assessed in response to ionic stress. These data, coupled with a measure of toxin intracellular to extracellular ratios, provide an insight into the physiology of STX export. Cylindrospermopsis raciborskii and Anabaena circinalis exhibited opposing responses under conditions of ionic stress. High Na(+) (10 mM) induced moderate alterations of transcription and STX localization, whereas high pH (pH 9) stimulated the greatest physiological response. Saxitoxin production and cellular localization are responsive to ionic strength, indicating a role of this molecule in the maintenance of cellular homeostasis.

  • proteogenomics of a saxitoxin producing and non toxic strain of Anabaena circinalis cyanobacteria in response to extracellular nacl and phosphate depletion
    Environmental Microbiology, 2016
    Co-Authors: Brett A. Neilan, Xiaomin Song, Paul M Dagostino, Michelle C. Moffitt
    Abstract:

    In Australia, saxitoxin production is strain dependent within the bloom-forming freshwater cyanobacterium Anabaena circinalis. Freshwater cyanobacteria are exposed to rapid fluctuations in environmental nutrient concentrations, and their adaption is vital for competition, succession and dominance. Two elements of environmental significance, phosphorus and sodium chloride, are proposed to play a role in bloom development and saxitoxin biosynthesis respectively. The aim of our study was to comparatively analyse the model saxitoxin-producing A. circinalis AWQC131C and non-toxic A. circinalis AWQC310F at the genomic level and proteomic level, in response to phosphate depletion and increased extracellular NaCl. When challenged, photosynthesis, carbon/nitrogen metabolisms, transcription/translation, oxidative stress and nutrient transport functional categories demonstrated the largest changes in protein abundance. In response to increased NaCl, SxtC, a protein conserved in all known saxitoxin biosynthetic pathways, was downregulated. Additionally, toxin quantification revealed a decrease in total saxitoxin and decarbomoyl-gonyautoxin2/3 content in response to the NaCl treatment. In response to phosphate depletion, the toxic and non-toxic strain displayed similar proteomic profiles, although the toxic strain did not alter the abundance of as many proteins as the non-toxic strain. These findings have important implications for the future, since response and adaption mechanisms are directly related to in situ dominance of cyanobacteria.

  • Comparative Proteomics Reveals That a Saxitoxin-Producing and a Nontoxic Strain of Anabaena circinalis Are Two Different Ecotypes
    Journal of proteome research, 2014
    Co-Authors: Paul M. D’agostino, Brett A. Neilan, Xiaomin Song, Michelle C. Moffitt
    Abstract:

    In Australia, saxitoxin production is restricted to the cyanobacterial species Anabaena circinalis and is strain-dependent. We aimed to characterize a saxitoxin-producing and nontoxic strain of A. circinalis at the proteomic level using iTRAQ. Seven proteins putatively involved in saxitoxin biosynthesis were identified within our iTRAQ experiment for the first time. The proteomic profile of the toxic A. circinalis was significantly different from the nontoxic strain, indicating that each is likely to inhabit a unique ecological niche. Under control growth conditions, the saxitoxin-producing A. circinalis displayed a higher abundance of photosynthetic, carbon fixation and nitrogen metabolic proteins. Differential abundance of these proteins suggests a higher intracellular C:N ratio and a higher concentration of intracellular 2-oxoglutarate in our toxic strain compared with the nontoxic strain. This may be a novel site for posttranslational regulation because saxitoxin biosynthesis putatively requires a 2-o...

  • Comparative Proteomics Reveals That a Saxitoxin-Producing and a Nontoxic Strain of Anabaena circinalis Are Two Different Ecotypes
    2014
    Co-Authors: Paul M. D’agostino, Brett A. Neilan, Xiaomin Song, Michelle C. Moffitt
    Abstract:

    In Australia, saxitoxin production is restricted to the cyanobacterial species Anabaena circinalis and is strain-dependent. We aimed to characterize a saxitoxin-producing and nontoxic strain of A. circinalis at the proteomic level using iTRAQ. Seven proteins putatively involved in saxitoxin biosynthesis were identified within our iTRAQ experiment for the first time. The proteomic profile of the toxic A. circinalis was significantly different from the nontoxic strain, indicating that each is likely to inhabit a unique ecological niche. Under control growth conditions, the saxitoxin-producing A. circinalis displayed a higher abundance of photosynthetic, carbon fixation and nitrogen metabolic proteins. Differential abundance of these proteins suggests a higher intracellular C:N ratio and a higher concentration of intracellular 2-oxoglutarate in our toxic strain compared with the nontoxic strain. This may be a novel site for posttranslational regulation because saxitoxin biosynthesis putatively requires a 2-oxoglutarate-dependent dioxygenase. The nontoxic A. circinalis was more abundant in proteins, indicating cellular stress. Overall, our study has provided the first insight into fundamental differences between a toxic and nontoxic strain of A. circinalis, indicating that they are distinct ecotypes

Susan I Blackburn - One of the best experts on this subject based on the ideXlab platform.

  • the influence of light quality on akinete formation and germination in the toxic cyanobacterium Anabaena circinalis
    Harmful Algae, 2009
    Co-Authors: Peter A Thompson, Ian Jameson, Susan I Blackburn
    Abstract:

    Abstract Physiological control of akinete formation and subsequent germination is likely to be important in understanding and predicting how natural populations of cyanobacteria respond to their environment. While previous research has indicated nutrient limitation may be important in akinete formation new results presented here indicate that in the toxic and bloom-forming species Anabaena circinalis there was a profound effect of spectral quality. Under 40 μmol photons m −2  s −1 photosynthetically active irradiance (PAR) of predominately red irradiance akinete production was maximal at 2.1 × 10 −4  akinetes vegetative cell −1  d −1 , some 3000 times greater than the 6.5 × 10 −8  akinetes vegetative cell −1  d −1 observed under equivalent PAR but predominately blue light. For cells grown under a range of predominantly red, white and green irradiance even short exposures to blue light reduced akinete formation rates by a factor of ten relative to controls, indicating that exposure to blue light inhibits akinete formation. Germination of akinetes was not influenced by the irradiance under which akinetes were formed: 88 ± 4.1% (mean ± 1 S.D.) of akinetes germinated with no evidence of an effect on germination success due to their production under predominately red, white or green irradiance (germination of akinetes produced under blue light was not tested). Spectral quality had a significant impact on both vegetative cell and germling growth rates. The results indicate a significant reduction in the cellular differentiation of A. circinalis vegetative cells into akinetes that is mediated by blue light. In an ecological context the production of akinetes will be greater in environments with less blue light; potentially including those with slower flow, more stratification, less vertical mixing and more turbidity. The resulting spatial pattern of akinete production is likely to influence the location of akinetes in sediments and the development of subsequent blooms from excysting germlings.

  • Ecophysiological influence of light and mixing on Anabaena circinalis (Nostocales, Cyanobacteria)
    European Journal of Phycology, 2005
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    The physiology (growth rate, biochemical composition and flotation rate) of the toxic cyanobacterium Anabaena circinalis was studied in relation to irradiance and mixing regime in two small-scale (250 ml or 1 l) batch culture experiments and one medium scale (1 m high, 4.4 l), semi-continuous microcosm experiment. In batch cultures, A. circinalis had a relatively high irradiance requirement as indicated by its compensation irradiance, E c (13 ± 2 μmol m−2 s−1). The growth efficiency (αg) of A. circinalis, estimated as the initial slope of the growth-irradiance curve , was in the mid to high range depending on the model applied (Monod: 0.33 ± 0.19 m2 mol−1, exponential: 0.43 ± 0.15 m2 mol−1). The flotation rate of the A. circinalis population was 0.69 ± 0.11 m d−1 at 100 μmol m−2 s−1 and decreased at higher irradiance to be negative at irradiances over 135 μmol m−2 s−1. In a microcosm experiment, different mixing intervals were tested (10 min (MIXED) and 48 h (CALM)) across three irradiance treatments. The...

  • the effect of changes in light availability caused by mixing on the growth of Anabaena circinalis nostocales cyanobacteria and aulacoseira sp centrales bacillariophyceae
    Phycologia, 2001
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    Experiments were undertaken to study the effects of vertical distribution controlled by mixing on the population growth of Australian isolates of the toxic cyanobacterium Anabaena circinalis and the diatom Aulacoseira sp.Transparent tubular microcosms were identically illuminated in all experiments, with a surface maximum irradiance of 225 μmol photons m - 2 2 s - 1 attenuating to a minimum of 18 μmol photons m - 2 s - 1 at the base of the microcosm at 1 m depth. In separate experiments, microcosms containing A. circinalis or Aulacoseira sp. were mixed at 10 min (MIXED treatment) or 48 h (CALM treatment) intervals to simulate well-mixed and calm environments, respectively. The vertical distribution of cells was predicted using a model that utilized growth-irradiance relationships and sinking and flotation rates measured during the experiments. For A. circinalis, there was no significant difference in population growth rate between MIXED and CALM treatments (MIXED, μ = 0.47 d - 1 ; CALM, μ = 0.45 d - 1 ). The predicted vertical distribution of A. circinalis was skewed toward the surface in the CALM treatment, indicating that an increased portion of the population received greater irradiance. However, both predicted and actual population growth were no greater in the CALM treatment, owing to the low flotation rate of the cells. Any light-harvesting advantage gained through buoyancy was insufficient to produce a significant difference in growth. Aulacoseira sp. had significantly different population growth rates in different treatments (MIXED, μ = 0.39 d - 1 ; CALM, μ = 0.28 d - 1 ). Predicted differences in the vertical distribution of Aulacoseira sp. indicate that a large proportion of the cellular population received reduced light as a consequence of sinking in the CALM treatment. These results indicate that population growth in Aulacoseira sp. is highly sensitive to reduced light caused by sinking from the well-lit surface waters. Our microcosm experiments suggest that, in the natural environment, reduced growth of Aulacoseira sp. in calm conditions in thermally stratified and/or low flow conditions would put it at a competitive disadvantage relative to A. circinalis.

  • the effect of changes in light availability caused by mixing on the growth of Anabaena circinalis nostocales cyanobacteria and aulacoseira sp centrales bacillariophyceae
    Phycologia, 2001
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    Experiments were undertaken to study the effects of vertical distribution controlled by mixing on the population growth of Australian isolates of the toxic cyanobacterium Anabaena circinalis and th...

  • effect of culture and bloom development and of sample storage on paralytic shellfish poisons in the cyanobacterium Anabaena circinalis
    Journal of Phycology, 1997
    Co-Authors: Andrew P Negri, Susan I Blackburn, Gary J Jones, Yasukatsu Oshima, Hideyuki Onodera
    Abstract:

    Paralytic shellfish poisons (PSPs) were detected in 24 of 31 bloom samples dominated by the cyanobacterium Anabaena circinalis Rabenhorst, collected from across Austraia. The ability to produce PSPs has been maintained in everal non-axenic strains of A. circinalis kept in culture, whereas strains that were non-toxin-producing when isolated have remained as such. PSPs were detected and quantified by high-performance liquid chromatography (HPLC), and the structures were confirmed by electrospray mass spectroscopy. The concentration of toxins in PSP positive samples ranged from 50 to 3400 μg.g-1 dry weight. Toxin profiles were always dominated by the N-sulfocarbamoyl-11-hydroxysulfate C toxins, C1 and C2 (44–85 mol%), with the remainder consisting of gonyautoxins-2, −3, and −5, decarbamoylgonyautoxins-2 and −3, saxitoxin, and decarbamoylraxitoxin. N1--hydroxy PSPs, commonly found in marine dinoflagellates, were absent, suggesting that A. circinalis lacks the enzyme responsible for N1--hydroxylation. On a dry weight basis, the amount of toxin in cultured Anabaena circinalis (strain ACMB06)rose significantly (P < 0.05)over time from 570 to 3400 μg.g.-1 cells in late stationary phase. However, there was no significant trend in cellular toxin quota (toxin per cell) over the life of the culture; this may be explained by variation in cell mass. On average, batch cultures of Anabaena circinalis contained 19% extracellular toxin, which increased slightly over the growth cycle and had a composition similar to that of the intracellular toxins. As cultures aged, the formation of decarbamoyl toxins and increases in theα-/β-epimer ratios of C toxins and gonyautoxins were observed. The variation in these components during stationary phase in culture was sufficient to explain the variation in relative PSP composition observed among natural bloom samples. Because decarbamoylgonyautoxins are much more toxic than C toxins on a molar basis, these transformations also lead to an increase in toxicity of the sample or bloom over time. The transformations of PSPs, which occur during aging and sample storage, render the comparison of PSPs by HPLC unreliable for phenotyping Anabaena circinalis, unless strains are cultured, harvested, and analyzed under standard conditions.

Yasukatsu Oshima - One of the best experts on this subject based on the ideXlab platform.

  • identification of a novel saxitoxin analogue 12β deoxygonyautoxin 3 in the cyanobacterium Anabaena circinalis ta04
    Toxins, 2019
    Co-Authors: Takashi Minowa, Yuko Cho, Keiichi Konoki, Yasukatsu Oshima, Mari Yotsuyamashita
    Abstract:

    Saxitoxin (STX) and its analogues, the potent voltage-gated sodium channel blockers, are biosynthesized by freshwater cyanobacteria and marine dinoflagellates. We previously identified several biosynthetic intermediates in the extract of the cyanobacterium, Anabaena circinalis (TA04), that are primarily produced during the early and middle stages in the biosynthetic pathway to produce STX. These findings allowed us to propose a putative biosynthetic pathway responsible for STX production based on the structures of these intermediates. In the present study, we identified 12β-deoxygonyautoxin 3 (12β-deoxyGTX3), a novel STX analogue produced by A. circinalis (TA04), by comparing the retention time and MS/MS fragmentation pattern with those of synthetic standards using LC-MS. The presence of this compound in A. circinalis (TA04) is consistent with stereoselective enzymatic oxidations at C11 and C12, and 11-O-sulfation, during the late stage of STX biosynthesis, as proposed in previous studies.

  • biosynthetic route towards saxitoxin and shunt pathway
    Scientific Reports, 2016
    Co-Authors: Shigeki Tsuchiya, Yuko Cho, Keiichi Konoki, Kazuo Nagasawa, Yasukatsu Oshima, Mari Yotsuyamashita
    Abstract:

    Saxitoxin, the most potent voltage-gated sodium channel blocker, is one of the paralytic shellfish toxins (PSTs) produced by cyanobacteria and dinoflagellates. Recently, putative biosynthetic genes of PSTs were reported in these microorganisms. We previously synthesized genetically predicted biosynthetic intermediates, Int-A' and Int-C'2, and also Cyclic-C' which was not predicted based on gene, and identified them all in the toxin-producing cyanobacterium Anabaena circinalis (TA04) and the dinoflagellate Alexandrium tamarense (Axat-2). This study examined the incorporation of (15)N-labeled intermediates into PSTs (C1 and C2) in A. circinalis (TA04). Conversions from Int-A' to Int-C'2, from Int-C'2 to Cyclic-C', and from Int-A' and Int-C'2 to C1 and C2 were indicated using high resolution-LC/MS. However, Cyclic-C' was not converted to C1 and C2 and was detected primarily in the extracellular medium. These results suggest that Int-A' and Int-C'2 are genuine precursors of PSTs, but Int-C'2 converts partially to Cyclic-C' which is a shunt product excreted to outside the cells. This paper provides the first direct demonstration of the biosynthetic route towards saxitoxin and a shunt pathway.

  • preparation of calibration standards of n1 h paralytic shellfish toxin analogues by large scale culture of cyanobacterium Anabaena circinalis ta04
    Marine Drugs, 2011
    Co-Authors: Ryuichi Watanabe, Toshiyuki Suzuki, Yasukatsu Oshima
    Abstract:

    Mouse bioassay is the official testing method to quantify paralytic shellfish toxins (PSTs) in bivalves. A number of alternative analytical methods have been reported. Some methods have been evaluated by a single laboratory validation. Among the different types of methods, chemical analyses are capable of identifying and quantifying the toxins, however a shortage of the necessary calibration standards hampers implementation of the chemical analyses in routine monitoring of PSTs in bivalves. In our present study, we studied preparation of major PST analogues as calibrants by large-scale cultivation of toxic freshwater cyanobacteria Anabaena circinalis TA04. The cells were steadily grown in 10 L bottle for 28 days. The primary N1-H toxins, C1/C2, were produced at a concentration of 1.3 ± 0.1 μmol/L. The intracellular and extracellular toxins occupied 80% and 20%, respectively. Over 220 μmol of the toxins was obtained from approximately 200 L of the culture over six months, demonstrating that it is sufficient to prepare saxitoxin analogues. The toxins were chemically converted to six N1-H analogues. Preparation of the analogues was carried out at relatively high yields (50-90%). The results indicate that our preparation method is useful to produce N1-H toxins. In our present study, detailed conditions for preparation of one of the rare N1-H analogues, gonyautoxin-5, were investigated.

  • Preparation of Calibration Standards of N1-H Paralytic Shellfish Toxin Analogues by Large-Scale Culture of
    2011
    Co-Authors: Cyanobacterium Anabaena Circinalis, Toshiyuki Suzuki, Ryuichi Watanabe, Yasukatsu Oshima
    Abstract:

    Abstract: Mouse bioassay is the official testing method to quantify paralytic shellfish toxins (PSTs) in bivalves. A number of alternative analytical methods have been reported. Some methods have been evaluated by a single laboratory validation. Among the different types of methods, chemical analyses are capable of identifying and quantifying the toxins, however a shortage of the necessary calibration standards hampers implementation of the chemical analyses in routine monitoring of PSTs in bivalves. In our present study, we studied preparation of major PST analogues as calibrants by large-scale cultivation of toxic freshwater cyanobacteria Anabaena circinalis TA04. The cells were steadily grown in 10 L bottle for 28 days. The primary N1-H toxins, C1/C2, were produced at a concentration of 1.3 ± 0.1 µmol/L. The intracellular and extracellular toxins occupied 80 % and 20%, respectively. Over 220 µmol of the toxins was obtained from approximately 200 L of the culture over six months, demonstrating that it is sufficient to prepare saxitoxin analogues. The toxins were chemically converted to six N1-H analogues. Preparation of the analogues was carried out at relatively high yields (50–90%). The results indicate that our preparation method is useful to produce N1-H toxins. In our present study, detailed conditions fo

  • effect of culture and bloom development and of sample storage on paralytic shellfish poisons in the cyanobacterium Anabaena circinalis
    Journal of Phycology, 1997
    Co-Authors: Andrew P Negri, Susan I Blackburn, Gary J Jones, Yasukatsu Oshima, Hideyuki Onodera
    Abstract:

    Paralytic shellfish poisons (PSPs) were detected in 24 of 31 bloom samples dominated by the cyanobacterium Anabaena circinalis Rabenhorst, collected from across Austraia. The ability to produce PSPs has been maintained in everal non-axenic strains of A. circinalis kept in culture, whereas strains that were non-toxin-producing when isolated have remained as such. PSPs were detected and quantified by high-performance liquid chromatography (HPLC), and the structures were confirmed by electrospray mass spectroscopy. The concentration of toxins in PSP positive samples ranged from 50 to 3400 μg.g-1 dry weight. Toxin profiles were always dominated by the N-sulfocarbamoyl-11-hydroxysulfate C toxins, C1 and C2 (44–85 mol%), with the remainder consisting of gonyautoxins-2, −3, and −5, decarbamoylgonyautoxins-2 and −3, saxitoxin, and decarbamoylraxitoxin. N1--hydroxy PSPs, commonly found in marine dinoflagellates, were absent, suggesting that A. circinalis lacks the enzyme responsible for N1--hydroxylation. On a dry weight basis, the amount of toxin in cultured Anabaena circinalis (strain ACMB06)rose significantly (P < 0.05)over time from 570 to 3400 μg.g.-1 cells in late stationary phase. However, there was no significant trend in cellular toxin quota (toxin per cell) over the life of the culture; this may be explained by variation in cell mass. On average, batch cultures of Anabaena circinalis contained 19% extracellular toxin, which increased slightly over the growth cycle and had a composition similar to that of the intracellular toxins. As cultures aged, the formation of decarbamoyl toxins and increases in theα-/β-epimer ratios of C toxins and gonyautoxins were observed. The variation in these components during stationary phase in culture was sufficient to explain the variation in relative PSP composition observed among natural bloom samples. Because decarbamoylgonyautoxins are much more toxic than C toxins on a molar basis, these transformations also lead to an increase in toxicity of the sample or bloom over time. The transformations of PSPs, which occur during aging and sample storage, render the comparison of PSPs by HPLC unreliable for phenotyping Anabaena circinalis, unless strains are cultured, harvested, and analyzed under standard conditions.

Malcolm A Mccausland - One of the best experts on this subject based on the ideXlab platform.

  • Ecophysiological influence of light and mixing on Anabaena circinalis (Nostocales, Cyanobacteria)
    European Journal of Phycology, 2005
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    The physiology (growth rate, biochemical composition and flotation rate) of the toxic cyanobacterium Anabaena circinalis was studied in relation to irradiance and mixing regime in two small-scale (250 ml or 1 l) batch culture experiments and one medium scale (1 m high, 4.4 l), semi-continuous microcosm experiment. In batch cultures, A. circinalis had a relatively high irradiance requirement as indicated by its compensation irradiance, E c (13 ± 2 μmol m−2 s−1). The growth efficiency (αg) of A. circinalis, estimated as the initial slope of the growth-irradiance curve , was in the mid to high range depending on the model applied (Monod: 0.33 ± 0.19 m2 mol−1, exponential: 0.43 ± 0.15 m2 mol−1). The flotation rate of the A. circinalis population was 0.69 ± 0.11 m d−1 at 100 μmol m−2 s−1 and decreased at higher irradiance to be negative at irradiances over 135 μmol m−2 s−1. In a microcosm experiment, different mixing intervals were tested (10 min (MIXED) and 48 h (CALM)) across three irradiance treatments. The...

  • the effect of changes in light availability caused by mixing on the growth of Anabaena circinalis nostocales cyanobacteria and aulacoseira sp centrales bacillariophyceae
    Phycologia, 2001
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    Experiments were undertaken to study the effects of vertical distribution controlled by mixing on the population growth of Australian isolates of the toxic cyanobacterium Anabaena circinalis and the diatom Aulacoseira sp.Transparent tubular microcosms were identically illuminated in all experiments, with a surface maximum irradiance of 225 μmol photons m - 2 2 s - 1 attenuating to a minimum of 18 μmol photons m - 2 s - 1 at the base of the microcosm at 1 m depth. In separate experiments, microcosms containing A. circinalis or Aulacoseira sp. were mixed at 10 min (MIXED treatment) or 48 h (CALM treatment) intervals to simulate well-mixed and calm environments, respectively. The vertical distribution of cells was predicted using a model that utilized growth-irradiance relationships and sinking and flotation rates measured during the experiments. For A. circinalis, there was no significant difference in population growth rate between MIXED and CALM treatments (MIXED, μ = 0.47 d - 1 ; CALM, μ = 0.45 d - 1 ). The predicted vertical distribution of A. circinalis was skewed toward the surface in the CALM treatment, indicating that an increased portion of the population received greater irradiance. However, both predicted and actual population growth were no greater in the CALM treatment, owing to the low flotation rate of the cells. Any light-harvesting advantage gained through buoyancy was insufficient to produce a significant difference in growth. Aulacoseira sp. had significantly different population growth rates in different treatments (MIXED, μ = 0.39 d - 1 ; CALM, μ = 0.28 d - 1 ). Predicted differences in the vertical distribution of Aulacoseira sp. indicate that a large proportion of the cellular population received reduced light as a consequence of sinking in the CALM treatment. These results indicate that population growth in Aulacoseira sp. is highly sensitive to reduced light caused by sinking from the well-lit surface waters. Our microcosm experiments suggest that, in the natural environment, reduced growth of Aulacoseira sp. in calm conditions in thermally stratified and/or low flow conditions would put it at a competitive disadvantage relative to A. circinalis.

  • the effect of changes in light availability caused by mixing on the growth of Anabaena circinalis nostocales cyanobacteria and aulacoseira sp centrales bacillariophyceae
    Phycologia, 2001
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    Experiments were undertaken to study the effects of vertical distribution controlled by mixing on the population growth of Australian isolates of the toxic cyanobacterium Anabaena circinalis and th...

Peter A Thompson - One of the best experts on this subject based on the ideXlab platform.

  • the influence of light quality on akinete formation and germination in the toxic cyanobacterium Anabaena circinalis
    Harmful Algae, 2009
    Co-Authors: Peter A Thompson, Ian Jameson, Susan I Blackburn
    Abstract:

    Abstract Physiological control of akinete formation and subsequent germination is likely to be important in understanding and predicting how natural populations of cyanobacteria respond to their environment. While previous research has indicated nutrient limitation may be important in akinete formation new results presented here indicate that in the toxic and bloom-forming species Anabaena circinalis there was a profound effect of spectral quality. Under 40 μmol photons m −2  s −1 photosynthetically active irradiance (PAR) of predominately red irradiance akinete production was maximal at 2.1 × 10 −4  akinetes vegetative cell −1  d −1 , some 3000 times greater than the 6.5 × 10 −8  akinetes vegetative cell −1  d −1 observed under equivalent PAR but predominately blue light. For cells grown under a range of predominantly red, white and green irradiance even short exposures to blue light reduced akinete formation rates by a factor of ten relative to controls, indicating that exposure to blue light inhibits akinete formation. Germination of akinetes was not influenced by the irradiance under which akinetes were formed: 88 ± 4.1% (mean ± 1 S.D.) of akinetes germinated with no evidence of an effect on germination success due to their production under predominately red, white or green irradiance (germination of akinetes produced under blue light was not tested). Spectral quality had a significant impact on both vegetative cell and germling growth rates. The results indicate a significant reduction in the cellular differentiation of A. circinalis vegetative cells into akinetes that is mediated by blue light. In an ecological context the production of akinetes will be greater in environments with less blue light; potentially including those with slower flow, more stratification, less vertical mixing and more turbidity. The resulting spatial pattern of akinete production is likely to influence the location of akinetes in sediments and the development of subsequent blooms from excysting germlings.

  • Ecophysiological influence of light and mixing on Anabaena circinalis (Nostocales, Cyanobacteria)
    European Journal of Phycology, 2005
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    The physiology (growth rate, biochemical composition and flotation rate) of the toxic cyanobacterium Anabaena circinalis was studied in relation to irradiance and mixing regime in two small-scale (250 ml or 1 l) batch culture experiments and one medium scale (1 m high, 4.4 l), semi-continuous microcosm experiment. In batch cultures, A. circinalis had a relatively high irradiance requirement as indicated by its compensation irradiance, E c (13 ± 2 μmol m−2 s−1). The growth efficiency (αg) of A. circinalis, estimated as the initial slope of the growth-irradiance curve , was in the mid to high range depending on the model applied (Monod: 0.33 ± 0.19 m2 mol−1, exponential: 0.43 ± 0.15 m2 mol−1). The flotation rate of the A. circinalis population was 0.69 ± 0.11 m d−1 at 100 μmol m−2 s−1 and decreased at higher irradiance to be negative at irradiances over 135 μmol m−2 s−1. In a microcosm experiment, different mixing intervals were tested (10 min (MIXED) and 48 h (CALM)) across three irradiance treatments. The...

  • the effect of changes in light availability caused by mixing on the growth of Anabaena circinalis nostocales cyanobacteria and aulacoseira sp centrales bacillariophyceae
    Phycologia, 2001
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    Experiments were undertaken to study the effects of vertical distribution controlled by mixing on the population growth of Australian isolates of the toxic cyanobacterium Anabaena circinalis and the diatom Aulacoseira sp.Transparent tubular microcosms were identically illuminated in all experiments, with a surface maximum irradiance of 225 μmol photons m - 2 2 s - 1 attenuating to a minimum of 18 μmol photons m - 2 s - 1 at the base of the microcosm at 1 m depth. In separate experiments, microcosms containing A. circinalis or Aulacoseira sp. were mixed at 10 min (MIXED treatment) or 48 h (CALM treatment) intervals to simulate well-mixed and calm environments, respectively. The vertical distribution of cells was predicted using a model that utilized growth-irradiance relationships and sinking and flotation rates measured during the experiments. For A. circinalis, there was no significant difference in population growth rate between MIXED and CALM treatments (MIXED, μ = 0.47 d - 1 ; CALM, μ = 0.45 d - 1 ). The predicted vertical distribution of A. circinalis was skewed toward the surface in the CALM treatment, indicating that an increased portion of the population received greater irradiance. However, both predicted and actual population growth were no greater in the CALM treatment, owing to the low flotation rate of the cells. Any light-harvesting advantage gained through buoyancy was insufficient to produce a significant difference in growth. Aulacoseira sp. had significantly different population growth rates in different treatments (MIXED, μ = 0.39 d - 1 ; CALM, μ = 0.28 d - 1 ). Predicted differences in the vertical distribution of Aulacoseira sp. indicate that a large proportion of the cellular population received reduced light as a consequence of sinking in the CALM treatment. These results indicate that population growth in Aulacoseira sp. is highly sensitive to reduced light caused by sinking from the well-lit surface waters. Our microcosm experiments suggest that, in the natural environment, reduced growth of Aulacoseira sp. in calm conditions in thermally stratified and/or low flow conditions would put it at a competitive disadvantage relative to A. circinalis.

  • the effect of changes in light availability caused by mixing on the growth of Anabaena circinalis nostocales cyanobacteria and aulacoseira sp centrales bacillariophyceae
    Phycologia, 2001
    Co-Authors: Malcolm A Mccausland, Peter A Thompson, Susan I Blackburn
    Abstract:

    Experiments were undertaken to study the effects of vertical distribution controlled by mixing on the population growth of Australian isolates of the toxic cyanobacterium Anabaena circinalis and th...