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Robert W. Sanders - One of the best experts on this subject based on the ideXlab platform.
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Mixotrophic activity and diversity of Antarctic marine protists in austral summer
Frontiers in Marine Science, 2018Co-Authors: Rebecca J. Gast, Scott A. Fay, Robert W. SandersAbstract:Identifying putative mixotrophic protist species in the environment is important for understanding their behavior, with the recovery of these species in culture essential for determining the triggers of feeding, grazing rates and overall impact on bacterial standing stocks. In this project, mixotroph abundances determined using tracer ingestion in water and sea ice samples collected in the Ross Sea, Antarctica during the summer of 2011 were compared with data from the spring (Ross Sea) and fall (Arctic) to examine the impacts of Bacterivory/mixotrophy. Mixotrophic nanoplankton were usually less abundant than heterotrophs, but consumed more of the bacterial standing stock per day due to relatively higher ingestion rates (1-7 bacteria mixotroph-1 h-1 vs. 0.1-4 bacteria heterotroph-1 h-1). Yet, even with these high rates observed in the Antarctic summer, mixotrophs appeared to have a smaller contribution to Bacterivory than in the Antarctic spring. Additionaly, putative mixotroph taxa were identified through incubation experiments accomplished with bromodeoxyuridine labeled bacteria as food, immunoprecipitation (IP) of labeled DNA, and amplification and high throughput sequencing of the eukaryotic ribosomal V9 region. Putative mixotroph OTUs were identified in the IP samples by taxonomic similarity to known phototroph taxa. OTUs that had increased abundance in IP samples compared to the non-IP samples from both surface and chlorophyll maximum (CM) depths were considered to represent active mixotrophy and include ones taxonomically similar to Dictyocha, Gymnodinium, Pentapharsodinium and Symbiodinium. These OTUs represent target taxa for isolation and laboratory experiments on triggers for mixotrophy, to be combined with qPCR to estimate their abundance, seasonal distribution and potential impact.
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temperature dependent phagotrophy and phototrophy in a mixotrophic chrysophyte
Journal of Phycology, 2016Co-Authors: Sarah Devaul Princiotta, Brian T. Smith, Robert W. SandersAbstract:The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m(-2) · s(-1) , with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m(-2) · s(-1) ). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in Bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m(-2) · s(-1) ), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%-30% of the carbon budget could be attributed to Bacterivory at low temperatures. Grazing experiments in nutrient-modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.
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Temperature‐dependent phagotrophy and phototrophy in a mixotrophic chrysophyte
Journal of phycology, 2016Co-Authors: Sarah Devaul Princiotta, Brian T. Smith, Robert W. SandersAbstract:The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m(-2) · s(-1) , with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m(-2) · s(-1) ). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in Bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m(-2) · s(-1) ), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%-30% of the carbon budget could be attributed to Bacterivory at low temperatures. Grazing experiments in nutrient-modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.
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Bacterivory by phototrophic picoplankton and nanoplankton in Arctic waters.
FEMS microbiology ecology, 2011Co-Authors: Robert W. Sanders, Rebecca J. GastAbstract:Mixotrophy, the combination of phototrophy and heterotrophy within the same individual, is widespread in oceanic systems. Yet, neither the presence nor ecological impact of mixotrophs has been identified in an Arctic marine environment. We quantified nano- and picoplankton during early autumn in the Beaufort Sea and Canada Basin and determined relative rates of Bacterivory by heterotrophs and mixotrophs. Results confirmed previous reports of low microbial biomass for Arctic communities in autumn. The impact of Bacterivory was relatively low, ranging from 0.6 × 103 to 42.8 × 103 bacteria mL−1 day−1, but it was often dominated by pico- or nanomixotrophs. From 1% to 7% of the photosynthetic picoeukaryotes were bacterivorous, while mixotrophic nanoplankton abundance comprised 1–22% of the heterotrophic and 2–32% of the phototrophic nanoplankton abundance, respectively. The estimated daily grazing impact was usually < 5% of the bacterial standing stock, but impacts as high as 25% occurred. Analysis of denaturing gradient gel electrophoresis (DGGE) band patterns indicated that communities from different depths at the same site were appreciably different and that there was a shift in community diversity at the midpoint of the cruise. Sequence information from DGGE bands reflected microbes related to those from other Arctic studies, particularly from the Beaufort Sea.
Karel Šimek - One of the best experts on this subject based on the ideXlab platform.
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Ecological Traits of the Algae-Bearing Tetrahymena utriculariae (Ciliophora) from Traps of the Aquatic Carnivorous Plant Utricularia reflexa.
The Journal of eukaryotic microbiology, 2016Co-Authors: Karel Šimek, Gianna Pitsch, Michaela M. Salcher, Dagmara Sirová, Tanja Shabarova, Lubomír Adamec, Thomas PoschAbstract:Trap fluid of aquatic carnivorous plants of the genus Utricularia hosts specific microbiomes consisting of commensal pro- and eukaryotes of largely unknown ecology. We examined the characteristics and dynamics of bacteria and the three dominant eukaryotes, i.e. the algae-bearing ciliate Tetrahymena utriculariae (Ciliophora), a green flagellate Euglena agilis (Euglenophyta), and the alga Scenedesmus alternans (Chlorophyta), associated with the traps of Utricularia reflexa. Our study focused on ecological traits and life strategies of the highly abundant ciliate whose biomass by far exceeds that of other eukaryotes and bacteria independent of the trap age. The ciliate was the only bacterivore in the traps, driving rapid turnover of bacterial standing stock. However, given the large size of the ciliate and the cell-specific uptake rates of bacteria we estimated that Bacterivory alone would likely be insufficient to support its apparent rapid growth in traps. We suggest that mixotrophy based on algal symbionts contributes significantly to the diet and survival strategy of the ciliate in the extreme (anaerobic, low pH) trap-fluid environment. We propose a revised concept of major microbial interactions in the trap fluid where ciliate Bacterivory plays a central role in regeneration of nutrients bound in rapidly growing bacterial biomass.
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spatio temporal patterns of bacterioplankton production and community composition related to phytoplankton composition and protistan Bacterivory in a dam reservoir
Aquatic Microbial Ecology, 2008Co-Authors: Karel Šimek, Jan Jezbera, Karel Hornák, Josef Hejzlar, Jirri Nedoma, Petr Znachor, Jaromir SedaAbstract:Seasonal changes in the abundance and production of epilimnetic bacterioplankton, protistan abundance and Bacterivory, and extracellular phytoplankton production (EPP) were stud- ied at 3 sampling stations (DAM, MIDDLE and RIVER) located along the longitudinal axis of the canyon-shaped, meso-eutrophic R ˇ imov reservoir (Czech Republic). We found that at the river inflow (RIVER) compared to lacustrine parts of the reservoir (MIDDLE and DAM), different sources of organic carbon and of bacterial mortality control bacterioplankton dynamics and community compo- sition. At the RIVER site, EPP accounted for a negligible part of bacterial carbon demand, thus indi- cating the prominent role of allochthonous sources of organic substrates in the river inflow. In addi- tion, protistan Bacterivory removed there, on average, only 9% of bacterial production. In contrast, at the lacustrine MIDDLE and DAM stations, protistan Bacterivory accounted for 47 and 78% of bacte- rial production, respectively. Moreover, at these stations EPP was an autochthonous source of organic carbon sufficient to meet bacterial carbon demand and EPP was tightly correlated with bacterial car- bon demand (DAM, r 2 = 0.589, p < 0.005; MIDDLE, r 2 = 0.716, p < 0.001). At the DAM site, we ana- lyzed changes in EPP in relationship to phytoplankton community dynamics and found that crypto- phytes were associated with EPP. Only 2 algal groups, cryptophytes in a spring-early-summer period and diatoms in a summer-fall period, clearly dominated the phytoplankton. Changes in phytoplank- ton composition were related to changes in bacterial community composition studied by means of group-specific rRNA-targeted oligonucleotide probes. A trend of increased proportions of certain bacterial groups, mainly of the genus-like R-BT065 subcluster of Betaproteobacteria, was detected for the periods of high EPP levels, dominated by cryptophytes. More than 52% of the seasonal vari- ability in the abundance of the R-BT065 cluster was explained by changing EPP levels that indicated a tight taxon-specific algal-bacterial relationship.
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Role of diatom-attached choanoflagellates of the genus Salpingoeca as pelagic bacterivores
Aquatic Microbial Ecology, 2004Co-Authors: Karel Šimek, Jan Jezbera, Karel Hornák, Jaroslav Vrba, Jaromir SedaAbstract:We studied the ecological role of choanoflagellates of the genus Salpingoeca (possibly S. amphoridium) attached to the colonial diatoms Asterionella formosa and Fragilaria crotonensis in the Rˇ imov reservoir (South Bohemia). The choanoflagellate was found only on these 2 species of diatoms (0 to 35 choanoflagellate cells per diatom colony). It is clearly identifiable in natural samples, and is a highly efficient planktonic bacterivore. In 2 field experiments (Expt 1 in June 2000 and Expt 2 in September 2002) we estimated in situ rates of Bacterivory using fluorescently labeled bacteria (FLB) as tracers. There was a linear increase in the number of FLB per choanoflagellate during the first 30 min of incubation, with only 8 to 16% of individuals within the natural populations displaying no ingestion of FLB. Taxon-specific bacteria uptake rate of Salpingoeca spp. was 35 to 65 bacteria cell -1 h -1 . In Expt 2, by manipulating phosphorus (P) and organic carbon availability (glucose), we also examined how alga host and bacterial prey abundances can affect the dynamics of Salpingoeca and of other bacterivorous heterotrophic nanoflagellates (HNF). P additions increased the growth of F. crotonensis and subsequently also that of the attached Salpingoeca sp. In contrast, glucose addi- tion produced a marked development of small, free-swimming chrysomonads which competed with the choanoflagellate for the bacteria. Overall, across all experimental treatments Salpingoeca spp. grazing accounted for 11 to 64% of the total protistan grazing and for 6 to 49% of the daily removal rate of the bacterial standing stock. Our data indicate that given a sufficient abundance of suitable host algae, which possibly provide a refuge from potential grazers, and efficient grazing of free- swimming HNF by zooplankton, this single choanoflagellate taxon can temporarily constitute the most important pelagic bacterivore in the reservoir.
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Longitudinal changes in protistan Bacterivory and bacterial production in two canyon-shaped reservoirs of different trophic status
Hydrobiologia, 2003Co-Authors: Jan Jezbera, Jiří Nedoma, Karel ŠimekAbstract:We studied bacterial production and mortality due to heterotrophic nanoflagellate (HNF) and ciliate grazing on longitudinal transects conducted on two canyon-shaped reservoirs of different trophic status, Řimov and Orlik (Czech republic). Special attention was paid to the changes in these processes related to depth, spatial distribution of sampling points, different periods of planktonic succession and to the taxon-specific Bacterivory of ciliates. Bacterial production (BP) in both reservoirs was, on average, reaching similar values (ranging from 1.2 × 106 to 4 × 106 bacteria ml−1 d−1). In Řimov (mesoeutrophic, mean retention time 100 days), when seasonally averaged, total protistan grazing accounted for 35% of BP and was consistantly lower in the layer R (layer with the same temperature and conductivity as the river inflow). On the contrary, the seasonal average for the Orlik reservoir (eutrophic, mean retention time of 23 days) showed roughly two times higher proportion of BP (70% of the total) removed by protists. In both reservoirs, there was little or no difference in contribution of ciliates and HNF to total protistan Bacterivory. Overall, oligotrichous ciliates were recognized as the major ciliate bacterivores (accounting for 67% and 48% of total ciliate Bacterivory in Řimov and Orlik, respectively) followed by peritrichous ciliates that contributed to total ciliate Bacterivory from 23% (Řimov) to 28% (Orlik). A small omnivorous oligotrichous ciliate Halteria cf. grandinella was the major bacterivore within the whole ciliate community in both reservoirs, contributing as much as 48 and 34% to the total ciliate Bacterivory, in the Řimov and Orlik reservoirs, respectively.
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Comparing the effects of resource enrichment and grazing on a bacterioplankton community of a meso-eutrophic reservoir
Aquatic Microbial Ecology, 2003Co-Authors: Karel Šimek, Karel Hornák, Urania Christaki, Jirí Nedoma, Markus G. Weinbauer, Michal Mašín, John R. DolanAbstract:We examined changes in a microbial community in reaction to shifts in predation pressure and resources in a meso-eutrophic reservoir. Manipulations consisted of size fractionation and either in situ incubation or transplantation from the dam area to the river area, which differed in P-availability. Three treatments, in which samples were incubated for 96 h in dialysis bags, were used: a bacterivore-free (
Carlos Pedrós-alió - One of the best experts on this subject based on the ideXlab platform.
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Comparative analysis shows that Bacterivory, not viral lysis, controls the abundance of heterotrophic prokaryotic plankton.
FEMS microbiology ecology, 2000Co-Authors: Carlos Pedrós-alió, Juan I. Calderón-paz, Josep M. GasolAbstract:Empirical models derived from literature data were used to compare the factors controlling prokaryotic abundance (PN) and prokaryotic heterotrophic production (PHP) in solar salterns. These empirical relationships were generated as multiple linear regressions with PN or PHP as dependent variables, while the independent variables were chosen to reflect the likely sources of organic matter, inorganic nutrients and temperature. These variables were then measured in solar salterns and the predictions made by the general relationships were compared to actual saltern values of PN and PHP. Saltern ponds of salinity higher than 100 per thousand departed significantly from the general relationships, while the ponds of salinity lower than 100 per thousand fitted well within the range of values predicted by the general models. The most likely explanation for the discrepancy of the former was the absence of Bacterivory. This hypothesis was tested with data from other very different aquatic systems: karstic lakes with anaerobic hypolimnia and two marine areas in the Mediterranean and the Southern Ocean. The anoxic regions of karstic lakes departed significantly from the predictions of the general model, while the oxic layers conformed to the predictions. As in the case of salterns, this difference could be explained by the presence of significant predation in the oxic, but not in the anoxic, layers of these lakes. Finally, two marine areas with similar predation pressure on prokaryotes but very different impacts of viral lysis were tested. In all cases, PN values conformed to the predictions, suggesting that lysis due to viruses is not the main factor controlling PN in aquatic systems, which is more likely to be determined by the balance between Bacterivory and resource supply. The present work also demonstrates the usefulness of empirical comparative analyses to generate predictions and to draw inferences on the functioning of microbial communities.
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Viral lysis and Bacterivory during a phytoplankton bloom in a coastal water microcosm
Applied and environmental microbiology, 1999Co-Authors: Núria Guixa-boixereu, Kristine Lysnes, Carlos Pedrós-alióAbstract:A few years ago Bacterivory was considered to be the most important bacterial-loss factor in aquatic environments (e.g., reference 22). More recently, however, viral infection has been found to account for a significant proportion of bacterial mortality in some aquatic environments (8, 34, 39, 42). The first attempt to incorporate viruses into the budget of microbial carbon transfer was done by Bratbak et al. (5). These authors measured viral lysis and Bacterivory simultaneously in a mesocosm experiment. However, they could not balance bacterial losses with both loss factors. Viral lysis exceeded bacterial heterotrophic production (BHP) by a factor of 6, while Bacterivory exceeded it by a factor of 2. Later, two studies, which measured viral lysis and Bacterivory simultaneously, found that both factors accounted for the same proportion of bacterial mortality (8, 34). However, another study showed a small contribution of viral lysis to bacterial mortality compared to Bacterivory (12). Recently, in a similar study from a eutrophic lake, grazers regulated bacterial production in the epilimnion, whereas in the anoxic hypolimnion was regulated by viral lysis (39). Thus, it is not clear in what situations viral lysis could prevail over Bacterivory in controlling bacterial abundance. Weinbauer and Peduzzi (42) concluded, by evaluating the relationship between viral and bacterial abundance, that viral infection could prevail over Bacterivory at a high bacterial concentration. These results were in agreement with the uncoupling found between bacteria and heterotrophic nanoflagellates at a high bacterial abundance (9). All of these studies were done in a steady-state situation in which cells and viruses showed small temporal fluctuations. Large variations in the abundance of organisms in short periods of time occur during phytoplankton blooms. Bratbak et al. (4) have studied the fluctuations in the abundance of virus-like particles (VLP) during a phytoplankton bloom. In their study they found a rapid increase in VLP abundance after the maximal bacterial abundance had been reached. These authors suggested that part of the bacterial population had been lysed by viruses. However, they did not quantify the proportion of bacterial mortality attributable to viral lysis during the bloom. During a phytoplankton bloom, a non-steady-state situation is established and the biological diversity of the environment decreases. Due to the specificity of viral attack, viruses could be a significant source of bacterial mortality in these conditions. The objective of the present study was to investigate the different proportions of bacterial mortality attributable to viral lysis or Bacterivory at different stages of a phytoplankton bloom. In order to avoid the difficulties associated with the drifting of water masses, a situation inherent to marine environments, we carried out a microcosm experiment. The appearance of a phytoplankton bloom was stimulated by adding nutrients to the natural-water sample. Changes in chlorophyll a, flagellate, bacterial, and VLP abundance were monitored over time by different counting methods. Bacterial heterotrophic production, Bacterivory, and viral lysis were also measured. The proportion of bacterial mortality due to viruses and to Bacterivory was then estimated. In this work, we could assess whether one factor prevailed over the other or whether both acted simultaneously at each stage of the bloom.
Sarah Devaul Princiotta - One of the best experts on this subject based on the ideXlab platform.
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temperature dependent phagotrophy and phototrophy in a mixotrophic chrysophyte
Journal of Phycology, 2016Co-Authors: Sarah Devaul Princiotta, Brian T. Smith, Robert W. SandersAbstract:The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m(-2) · s(-1) , with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m(-2) · s(-1) ). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in Bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m(-2) · s(-1) ), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%-30% of the carbon budget could be attributed to Bacterivory at low temperatures. Grazing experiments in nutrient-modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.
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Temperature‐dependent phagotrophy and phototrophy in a mixotrophic chrysophyte
Journal of phycology, 2016Co-Authors: Sarah Devaul Princiotta, Brian T. Smith, Robert W. SandersAbstract:The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m(-2) · s(-1) , with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m(-2) · s(-1) ). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in Bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m(-2) · s(-1) ), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%-30% of the carbon budget could be attributed to Bacterivory at low temperatures. Grazing experiments in nutrient-modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.
Per Juel Hansen - One of the best experts on this subject based on the ideXlab platform.
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Mixotrophy in Chlorophytes and Haptophytes-Effect of Irradiance, Macronutrient, Micronutrient and Vitamin Limitation.
Frontiers in microbiology, 2018Co-Authors: Ruth Anderson, Sophie Charvet, Per Juel HansenAbstract:Chlorophytes and haptophytes are key contributors to global phytoplankton biomass and productivity. Mixotrophic Bacterivory has been detected for both groups, but a shortage of studies with cultured representatives hinders a consistent picture of the ecological relevance and regulation of this trophic strategy. Here, the growth, primary production, fraction of feeding cells (acidotropic probes) and Bacterivory rates (surrogate prey) are tested for two species of the chlorophyte genus Nephroselmis and the haptophyte Isochrysis galbana under contrasting regimes of light (high vs. low) and nutrients (non-limited and macronutrient-, micronutrient- and vitamin-limited), at low bacterial concentrations (
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Mixotrophic Phytoflagellate Bacterivory Field Measurements Strongly Biased by Standard Approaches: A Case Study.
Frontiers in microbiology, 2017Co-Authors: Ruth Anderson, Klaus Jürgens, Per Juel HansenAbstract:Bacterivory among small (≤ 20 μm) phytoflagellates (SP) is increasingly recognized as a globally relevant phenomenon, impacting a wide range of aspects from primary production levels to marine fisheries. However, to correctly parametrize mixotrophic SP in biogeochemical and food web models, a better understanding of the magnitude and regulation of in situ SP feeding is urgently needed. Current methods to determine SP Bacterivory in the field may introduce biases by treating these organisms as equivalent to heterotrophic nanoflagellates (HNF). In the present case study we experimentally tested two generally employed assumptions of such studies: (A) Bacterivory rates of the whole SP community and of distinct SP groups remain constant over `short´ time scales (hours to a day) and (B) SP community ingestion rates approximate the average ingestion rate of all feeding individuals. Food vacuole markers (acidotropic probes), were applied along the diel cycle at 3 stations in December 2015, and May and June 2016. In December and June, surrogate prey (fluorescently labelled bacteria) were used in parallel at one sampling station. Sampling at different times of day produced an up to 4-fold difference in estimates of SP daily bacterivorous impact. In contrast, daily Bacterivory estimates for HNF remained constant in almost all cases. The perceived principal SP bacterivorous groups also shifted strongly. As an example, picoeukaryotes dominated total SP Bacterivory in daylight hours but completely ceased to feed at night. Finally, a large fraction of the SP community was not feeding at all time points tested. This lead to significant errors in estimated ingestion rates determined using the whole SP community, being up to 16 times lower than those determined solely for actively feeding mixotrophic SP. Overall, this case study indicates that applying the two commonly used premises outlined above can introduce significant biases and considerably alter our perception of mixotrophy in a given system.
