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Andrew Stevenson - One of the best experts on this subject based on the ideXlab platform.
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Glycerol enhances fungal germination at the water‐activity limit for life
Environmental Microbiology, 2016Co-Authors: Andrew Stevenson, Su-lin L. Leong, Gerhard Kminek, Jan Dijksterhuis, Philip G. Hamill, Angel Medina, John D. Rummel, David J. Timson, Naresh Magan, John E. HallsworthAbstract:For the most-extreme fungal Xerophiles, metabolic activity and cell division typically halts between 0.700 and 0.640 water activity (approximately 70.0-64.0% relative humidity). Here, we investigate whether glycerol can enhance Xerophile germination under acute water-activity regimes, using an experimental system which represents the biophysical limit of Earth's biosphere. Spores from a variety of species, including Aspergillus penicillioides, Eurotium halophilicum, Xerochrysium xerophilum (formerly Chrysosporium xerophilum) and Xeromyces bisporus, were produced by cultures growing on media supplemented with glycerol (and contained up to 189 mg glycerol g dry spores-1 ). The ability of these spores to germinate, and the kinetics of germination, were then determined on a range of media designed to recreate stresses experienced in microbial habitats or anthropogenic systems (with water-activities from 0.765 to 0.575). For A. penicillioides, Eurotium amstelodami, E. halophilicum, X. xerophilum and X. bisporus, germination occurred at lower water-activities than previously recorded (0.640, 0.685, 0.651, 0.664 and 0.637 respectively). In addition, the kinetics of germination at low water-activities were substantially faster than those reported previously. Extrapolations indicated theoretical water-activity minima below these values; as low as 0.570 for A. penicillioides and X. bisporus. Glycerol is present at high concentrations (up to molar levels) in many types of microbial habitat. We discuss the likely role of glycerol in expanding the water-activity limit for microbial cell function in relation to temporal constraints and location of the microbial cell or habitat. The findings reported here have also critical implications for understanding the extremes of Earth's biosphere; for understanding the potency of disease-causing microorganisms; and in biotechnologies that operate at the limits of microbial function.
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Water‐, pH‐ and temperature relations of germination for the extreme Xerophiles Xeromyces bisporus (FRR 0025), Aspergillus penicillioides (JH06THJ) and Eurotium halophilicum (FRR 2471)
Microbial Biotechnology, 2016Co-Authors: Andrew Stevenson, Jan Dijksterhuis, Philip G. Hamill, John E. HallsworthAbstract:Water activity, temperature and pH are determinants for biotic activity of cellular systems, biosphere function and, indeed, for all life processes. This study was carried out at high concentrations of glycerol, which concurrently reduces water activity and acts as a stress protectant, to characterize the biophysical capabilities of the most extremely xerophilic organisms known. These were the fungal Xerophiles: Xeromyces bisporus (FRR 0025), Aspergillus penicillioides (JH06THJ) and Eurotium halophilicum (FRR 2471). High-glycerol spores were produced and germination was determined using 38 media in the 0.995-0.637 water activity range, 33 media in the 2.80-9.80 pH range and 10 incubation temperatures, from 2 to 50°C. Water activity was modified by supplementing media with glycerol+sucrose, glycerol+NaCl and glycerol+NaCl+sucrose which are known to be biologically permissive for X. bisporus, A. penicillioides and E. halophilicum respectively. The windows and rates for spore germination were quantified for water activity, pH and temperature; symmetry/asymmetry of the germination profiles were then determined in relation to supra- and sub-optimal conditions; and pH- and temperature optima for extreme xerophilicity were quantified. The windows for spore germination were ~1 to 0.637 water activity, pH 2.80-9.80 and > 10 and < 44°C, depending on strain. Germination profiles in relation to water activity and temperature were asymmetrical because conditions known to entropically disorder cellular macromolecules, i.e. supra-optimal water activity and high temperatures, were severely inhibitory. Implications of these processes were considered in relation to the in-situ ecology of extreme conditions and environments; the study also raises a number of unanswered questions which suggest the need for new lines of experimentation.
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Concomitant osmotic and chaotropicity-induced stresses in Aspergillus wentii: compatible solutes determine the biotic window
Current Genetics, 2015Co-Authors: Flávia Lima Alves, Terry J Mcgenity, Andrew Stevenson, Esther Baxter, Jenny L. M. Gillion, Fakhrossadat Hejazi, Sandra Hayes, Ian E. G. Morrison, Bernard A. Prior, Drauzio E. N. RangelAbstract:Whereas osmotic stress response induced by solutes has been well-characterized in fungi, less is known about the other activities of environmentally ubiquitous substances. The latest methodologies to define, identify and quantify chaotropicity, i.e. substance-induced destabilization of macromolecular systems, now enable new insights into microbial stress biology (Cray et al. in Curr Opin Biotechnol 33:228–259, 2015a , doi: 10.1016/j.copbio.2015.02.010 ; Ball and Hallsworth in Phys Chem Chem Phys 17:8297–8305, 2015 , doi: 10.1039/C4CP04564E ; Cray et al. in Environ Microbiol 15:287–296, 2013a , doi: 10.1111/1462-2920.12018 ). We used Aspergillus wentii , a paradigm for extreme solute-tolerant fungal Xerophiles, alongside yeast cell and enzyme models ( Saccharomyces cerevisiae and glucose-6-phosphate dehydrogenase) and an agar-gelation assay, to determine growth-rate inhibition, intracellular compatible solutes, cell turgor, inhibition of enzyme activity, substrate water activity, and stressor chaotropicity for 12 chemically diverse solutes. These stressors were found to be: (i) osmotically active (and typically macromolecule-stabilizing kosmotropes), including NaCl and sorbitol; (ii) weakly to moderately chaotropic and non-osmotic, these were ethanol, urea, ethylene glycol; (iii) highly chaotropic and osmotically active, i.e. NH_4NO_3, MgCl_2, guanidine hydrochloride, and CaCl_2; or (iv) inhibitory due primarily to low water activity, i.e. glycerol. At ≤0.974 water activity, Aspergillus cultured on osmotically active stressors accumulated low- M _r polyols to ≥100 mg g dry weight^−1. Lower- M _r polyols (i.e. glycerol, erythritol and arabitol) were shown to be more effective for osmotic adjustment; for higher- M _r polyols such as mannitol, and the disaccharide trehalose, water-activity values for saturated solutions are too high to be effective; i.e. 0.978 and 0.970 (25 ºC). The highly chaotropic, osmotically active substances exhibited a stressful level of chaotropicity at physiologically relevant concentrations (20.0–85.7 kJ kg^−1). We hypothesized that the kosmotropicity of compatible solutes can neutralize chaotropicity, and tested this via in-vitro agar-gelation assays for the model chaotropes urea, NH_4NO_3, phenol and MgCl_2. Of the kosmotropic compatible solutes, the most-effective protectants were trimethylamine oxide and betaine; but proline, dimethyl sulfoxide, sorbitol, and trehalose were also effective, depending on the chaotrope. Glycerol, by contrast (a chaotropic compatible solute used as a negative control) was relatively ineffective. The kosmotropic activity of compatible solutes is discussed as one mechanism by which these substances can mitigate the activities of chaotropic stressors in vivo. Collectively, these data demonstrate that some substances concomitantly induce chaotropicity-mediated and osmotic stresses, and that compatible solutes ultimately define the biotic window for fungal growth and metabolism. The findings have implications for the validity of ecophysiological classifications such as ‘halophile’ and ‘polyextremophile’; potential contamination of life-support systems used for space exploration; and control of mycotoxigenic fungi in the food-supply chain.
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Multiplication of microbes below 0.690 water activity: Implications for terrestrial and extraterrestrial life
Environmental Microbiology, 2015Co-Authors: Andrew Stevenson, Jonathan A. Cray, Mark Fox-powell, Terence P. Kee, Jurgen Burkhardt, Terry J Mcgenity, Gerhard Kminek, Jan Dijksterhuis, Charles S Cockell, Kenneth N. TimmisAbstract:Since a key requirement of known life forms is available water (water activity; aw ), recent searches for signatures of past life in terrestrial and extraterrestrial environments have targeted places known to have contained significant quantities of biologically available water. However, early life on Earth inhabited high-salt environments, suggesting an ability to withstand low water-activity. The lower limit of water activity that enables cell division appears to be ∼ 0.605 which, until now, was only known to be exhibited by a single eukaryote, the sugar-tolerant, fungal Xerophile Xeromyces bisporus. The first forms of life on Earth were, though, prokaryotic. Recent evidence now indicates that some halophilic Archaea and Bacteria have water-activity limits more or less equal to those of X. bisporus. We discuss water activity in relation to the limits of Earth's present-day biosphere; the possibility of microbial multiplication by utilizing water from thin, aqueous films or non-liquid sources; whether prokaryotes were the first organisms able to multiply close to the 0.605-aw limit; and whether extraterrestrial aqueous milieux of ≥ 0.605 aw can resemble fertile microbial habitats found on Earth.
Jan Dijksterhuis - One of the best experts on this subject based on the ideXlab platform.
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Glycerol enhances fungal germination at the water‐activity limit for life
Environmental Microbiology, 2016Co-Authors: Andrew Stevenson, Su-lin L. Leong, Gerhard Kminek, Jan Dijksterhuis, Philip G. Hamill, Angel Medina, John D. Rummel, David J. Timson, Naresh Magan, John E. HallsworthAbstract:For the most-extreme fungal Xerophiles, metabolic activity and cell division typically halts between 0.700 and 0.640 water activity (approximately 70.0-64.0% relative humidity). Here, we investigate whether glycerol can enhance Xerophile germination under acute water-activity regimes, using an experimental system which represents the biophysical limit of Earth's biosphere. Spores from a variety of species, including Aspergillus penicillioides, Eurotium halophilicum, Xerochrysium xerophilum (formerly Chrysosporium xerophilum) and Xeromyces bisporus, were produced by cultures growing on media supplemented with glycerol (and contained up to 189 mg glycerol g dry spores-1 ). The ability of these spores to germinate, and the kinetics of germination, were then determined on a range of media designed to recreate stresses experienced in microbial habitats or anthropogenic systems (with water-activities from 0.765 to 0.575). For A. penicillioides, Eurotium amstelodami, E. halophilicum, X. xerophilum and X. bisporus, germination occurred at lower water-activities than previously recorded (0.640, 0.685, 0.651, 0.664 and 0.637 respectively). In addition, the kinetics of germination at low water-activities were substantially faster than those reported previously. Extrapolations indicated theoretical water-activity minima below these values; as low as 0.570 for A. penicillioides and X. bisporus. Glycerol is present at high concentrations (up to molar levels) in many types of microbial habitat. We discuss the likely role of glycerol in expanding the water-activity limit for microbial cell function in relation to temporal constraints and location of the microbial cell or habitat. The findings reported here have also critical implications for understanding the extremes of Earth's biosphere; for understanding the potency of disease-causing microorganisms; and in biotechnologies that operate at the limits of microbial function.
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Water‐, pH‐ and temperature relations of germination for the extreme Xerophiles Xeromyces bisporus (FRR 0025), Aspergillus penicillioides (JH06THJ) and Eurotium halophilicum (FRR 2471)
Microbial Biotechnology, 2016Co-Authors: Andrew Stevenson, Jan Dijksterhuis, Philip G. Hamill, John E. HallsworthAbstract:Water activity, temperature and pH are determinants for biotic activity of cellular systems, biosphere function and, indeed, for all life processes. This study was carried out at high concentrations of glycerol, which concurrently reduces water activity and acts as a stress protectant, to characterize the biophysical capabilities of the most extremely xerophilic organisms known. These were the fungal Xerophiles: Xeromyces bisporus (FRR 0025), Aspergillus penicillioides (JH06THJ) and Eurotium halophilicum (FRR 2471). High-glycerol spores were produced and germination was determined using 38 media in the 0.995-0.637 water activity range, 33 media in the 2.80-9.80 pH range and 10 incubation temperatures, from 2 to 50°C. Water activity was modified by supplementing media with glycerol+sucrose, glycerol+NaCl and glycerol+NaCl+sucrose which are known to be biologically permissive for X. bisporus, A. penicillioides and E. halophilicum respectively. The windows and rates for spore germination were quantified for water activity, pH and temperature; symmetry/asymmetry of the germination profiles were then determined in relation to supra- and sub-optimal conditions; and pH- and temperature optima for extreme xerophilicity were quantified. The windows for spore germination were ~1 to 0.637 water activity, pH 2.80-9.80 and > 10 and < 44°C, depending on strain. Germination profiles in relation to water activity and temperature were asymmetrical because conditions known to entropically disorder cellular macromolecules, i.e. supra-optimal water activity and high temperatures, were severely inhibitory. Implications of these processes were considered in relation to the in-situ ecology of extreme conditions and environments; the study also raises a number of unanswered questions which suggest the need for new lines of experimentation.
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Multiplication of microbes below 0.690 water activity: Implications for terrestrial and extraterrestrial life
Environmental Microbiology, 2015Co-Authors: Andrew Stevenson, Jonathan A. Cray, Mark Fox-powell, Terence P. Kee, Jurgen Burkhardt, Terry J Mcgenity, Gerhard Kminek, Jan Dijksterhuis, Charles S Cockell, Kenneth N. TimmisAbstract:Since a key requirement of known life forms is available water (water activity; aw ), recent searches for signatures of past life in terrestrial and extraterrestrial environments have targeted places known to have contained significant quantities of biologically available water. However, early life on Earth inhabited high-salt environments, suggesting an ability to withstand low water-activity. The lower limit of water activity that enables cell division appears to be ∼ 0.605 which, until now, was only known to be exhibited by a single eukaryote, the sugar-tolerant, fungal Xerophile Xeromyces bisporus. The first forms of life on Earth were, though, prokaryotic. Recent evidence now indicates that some halophilic Archaea and Bacteria have water-activity limits more or less equal to those of X. bisporus. We discuss water activity in relation to the limits of Earth's present-day biosphere; the possibility of microbial multiplication by utilizing water from thin, aqueous films or non-liquid sources; whether prokaryotes were the first organisms able to multiply close to the 0.605-aw limit; and whether extraterrestrial aqueous milieux of ≥ 0.605 aw can resemble fertile microbial habitats found on Earth.
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Phylogeny and intraspecific variation of the extreme Xerophile, Xeromyces bisporus
Fungal Biology, 2011Co-Authors: Olga Vinnere Pettersson, Henrik Lantz, Su-lin L. Leong, Therese Rice, Jos Houbraken, Jan Dijksterhuis, Robert A. Samson, Johan SchnürerAbstract:The filamentous ascomycete Xeromyces bisporus is an extreme Xerophile able to grow down to a water activity of 0.62. We have inferred the phylogenetic position of Xeromyces in relation to other xerophilic and xerotolerant fungi in the order Eurotiales. Using nrDNA and betatubulin sequences, we show that it is more closely related to the xerophilic foodborne species of the genus Chrysosporium, than to the genus Monascus. The taxonomy of X. bisporus and Monascus is discussed. Based on physiological, morphological, and phylogenetic distinctiveness, we suggest that Xeromyces should be retained as a separate genus.
Ailsa D. Hocking - One of the best experts on this subject based on the ideXlab platform.
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TWO NEW SPECIES OF XEROPHILIC FUNGI AND A FURTHER RECORD OF EUROTIUM HALOPHILICUM
Mycologia, 2018Co-Authors: Ailsa D. Hocking, John I PittAbstract:Two new species of xerophilic fungi are described: Geomyces pulvereus Hocking & Pitt, and Monascus eremophilus Hocking & Pitt. The Monascus species is an obligate Xerophile, which does not appear to have an anamorphic state. A further occurrence of Eurotium halophilicum is reported, and a full description of this rarely encountered species is given. During the course of investigations into spoilage of various low water activity (aw) foodstuffs and commodities over several years, three unusual xerophilic fungi were isolated. One was identified as Eurotium halophilicum Christensen et al., a rarely encountered Xerophile, and it was concluded that the other isolates belonged to two previously undescribed species. Although one species is represented by only a single isolate, and the other by only two isolates, the new taxa are sufficiently distinctive to warrant description as new species. E. halophilicum has not been reported in the literature since it was described in 1959.
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Spoilage of stored, processed and preserved foods
Fungi and Food Spoilage, 2009Co-Authors: John I Pitt, Ailsa D. HockingAbstract:It is trite to say that dried foods must be kept dry, heat processed foods must be heated enough to inactivate all relevant spores, and preservative concentrations must be high enough to inhibit all fungi. The science of preserving foods, like so many other disciplines, requires compromise. Really dry foods, i.e. of a safe aw, may be impossible to obtain for climatic or economic reasons, or be unacceptable to the consumer; a sufficient heat process may destroy desirable flavours; and permitted preservative levels are set by law. Some fungi, by virtue of specific attributes, simply cannot be processed out of certain types of foods. Of particular importance are Xeromyces bisporus and Zygosaccharomyces rouxii — extreme Xerophiles which grow in concentrated foods; Byssochlamys spp. and Neosartorya fischeri with ascospores of very high heat resistance which can survive heat processing and grow in heat processed acid foods; and Zygosaccharomyces bailii, a preservative resistant yeast. Making foods safe from these fungi requires that they be absent from raw materials or destroyed by pasteurisation, and then excluded from the processing and packing lines.
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eLS - Fungal Xerophiles (Osmophiles)
eLS, 2001Co-Authors: Ailsa D. HockingAbstract:Xerophilic fungi are yeasts and moulds that are capable of growth at or below a water activity (aw) of 0.85. These microorganisms have developed physiological mechanisms that enable their biochemical pathways to function in concentrated environments. As a group they are extremely important in the spoilage of many processed foods and stored commodities. Keywords: xerophilic fungi; water activity; osmophiles; yeasts; food spoilage
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Some Considerations When Analyzing Foods for the Presence of Xerophilic Fungi.
Journal of Food Protection, 1990Co-Authors: Larry R. Beuchat, Ailsa D. HockingAbstract:: Foodborne fungi capable of growing at reduced water activity (aw) are described as xerophilic. Some xerophilic fungi will not grow or grow very slowly at aw values characteristic of media traditionally used to enumerate yeasts and molds in foods. Populations of Xerophiles may therefore be underestimated or go undetected. A brief review of the habitats and physiology of Xerophiles, followed by a description of media and methods available for detection, enumeration, and a key for identification are presented.
Rita Y. Cavero - One of the best experts on this subject based on the ideXlab platform.
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Ectomycorrhizae and vascular plants growing in brûlés as indicators of below and above ground microecology of black truffle production areas in Navarra (Northern Spain)
Biodiversity and Conservation, 2010Co-Authors: Begoña González-armada, Ana M. Miguel, Rita Y. CaveroAbstract:The diversity below (ectomycorrhizae) and above (vascular flora) ground in brûlés of black truffle production areas have been studied together for the first time, both in plantations and in natural areas, as possible indicators of the microecology of these zones. Studies on the ectomycorrhizal community of mature plantations are scarce. However, monitoring the dynamics of such systems is important to understand the conditions that promote truffle fructification. In the study described here the most frequent ectomycorrhizae are Tuber melanosporum and Quercirrhiza quadratum . In the plantations, Q. quadratum is the most abundant morphotype and in the natural area it is Cenococcum geophilum . The development of truffle ecosystems involves the appearance of competitor species with wide networks of hyphae and rhizomorphs. On the other hand, there are few studies concerning the special composition of the vascular flora growing in brûlés . We identified 199 taxa, most of them Mediterranean or Eurosiberian Xerophiles and therophytes. This is consistent with the ecology of truffle production areas (dry, sunny and stony). These plants are heavily influenced by the inhibiting substances produced by the truffle and, as a result, they suffer from inhibited growth and in some cases cannot complete their life cycle.
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Ectomycorrhizae and vascular plants growing in brûlés as indicators of below and above ground microecology of black truffle production areas in Navarra (Northern Spain)
Biodiversity and Conservation, 2010Co-Authors: Begoña González-armada, Ana M. Miguel, Rita Y. CaveroAbstract:The diversity below (ectomycorrhizae) and above (vascular flora) ground in brules of black truffle production areas have been studied together for the first time, both in plantations and in natural areas, as possible indicators of the microecology of these zones. Studies on the ectomycorrhizal community of mature plantations are scarce. However, monitoring the dynamics of such systems is important to understand the conditions that promote truffle fructification. In the study described here the most frequent ectomycorrhizae are Tuber melanosporum and Quercirrhiza quadratum. In the plantations, Q. quadratum is the most abundant morphotype and in the natural area it is Cenococcum geophilum. The development of truffle ecosystems involves the appearance of competitor species with wide networks of hyphae and rhizomorphs. On the other hand, there are few studies concerning the special composition of the vascular flora growing in brules. We identified 199 taxa, most of them Mediterranean or Eurosiberian Xerophiles and therophytes. This is consistent with the ecology of truffle production areas (dry, sunny and stony). These plants are heavily influenced by the inhibiting substances produced by the truffle and, as a result, they suffer from inhibited growth and in some cases cannot complete their life cycle.
Kenneth N. Timmis - One of the best experts on this subject based on the ideXlab platform.
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Multiplication of microbes below 0.690 water activity: Implications for terrestrial and extraterrestrial life
Environmental Microbiology, 2015Co-Authors: Andrew Stevenson, Jonathan A. Cray, Mark Fox-powell, Terence P. Kee, Jurgen Burkhardt, Terry J Mcgenity, Gerhard Kminek, Jan Dijksterhuis, Charles S Cockell, Kenneth N. TimmisAbstract:Since a key requirement of known life forms is available water (water activity; aw ), recent searches for signatures of past life in terrestrial and extraterrestrial environments have targeted places known to have contained significant quantities of biologically available water. However, early life on Earth inhabited high-salt environments, suggesting an ability to withstand low water-activity. The lower limit of water activity that enables cell division appears to be ∼ 0.605 which, until now, was only known to be exhibited by a single eukaryote, the sugar-tolerant, fungal Xerophile Xeromyces bisporus. The first forms of life on Earth were, though, prokaryotic. Recent evidence now indicates that some halophilic Archaea and Bacteria have water-activity limits more or less equal to those of X. bisporus. We discuss water activity in relation to the limits of Earth's present-day biosphere; the possibility of microbial multiplication by utilizing water from thin, aqueous films or non-liquid sources; whether prokaryotes were the first organisms able to multiply close to the 0.605-aw limit; and whether extraterrestrial aqueous milieux of ≥ 0.605 aw can resemble fertile microbial habitats found on Earth.
