TY - JOUR
T1 - Water-, pH- and temperature relations of germination for the extreme xerophiles Xeromyces bisporus (FRR 0025), Aspergillus penicillioides (JH06THJ) and Eurotium halophilicum (FRR 2471)
AU - Stevenson, Andrew
AU - Hamill, Philip G
AU - Dijksterhuis, Jan
AU - Hallsworth, John E
N1 - © 2016 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.
PY - 2017/3
Y1 - 2017/3
N2 - 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.
AB - 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.
U2 - 10.1111/1751-7915.12406
DO - 10.1111/1751-7915.12406
M3 - Article
C2 - 27562192
JO - Microbial Biotechnology
JF - Microbial Biotechnology
SN - 1751-7907
ER -