A decrease in bulk water and mannitol and accumulation of trehalose and trehalose‐based oligosaccharides define a two‐stage maturation process towards extreme stress resistance in ascospores of Neosartorya fischeri (Aspergillus fischeri)

Abstract

Fungal propagules survive stresses better than vegetative cells. Neosartorya fischeri, an Aspergillus teleomorph, forms ascospores that survive high temperatures or drying followed by heat. Not much is known about maturation and development of extreme stress resistance in fungal cells. This study provides a novel two-step model for the acquisition of extreme stress resistance and entry into dormancy. Ascospores of 11- and 15-day-old cultures exhibited heat resistance, physiological activity, accumulation of compatible solutes and a steep increase in cytoplasmic viscosity. Electron spin resonance spectroscopy indicated that this stage is associated with the removal of bulk water and an increase of chemical stability. Older ascospores from 15- to 50-day-old cultures showed no changes in compatible solute content and cytoplasmic viscosity, but did exhibit a further increase of heat resistance and redox stability with age. This stage was also characterized by changes in the composition of the mixture of compatible solutes. Mannitol levels decreased and the relative quantities of trehalose and trehalose-based oligosaccharides increased. Dormant ascospores of N. fischeri survive in low-water habitats. After activation of the germination process, the stress resistance decreases, compatible solutes are degraded and the cellular viscosity drops. After 5 h, the hydrated cells enter the vegetative stage and redox stability has decreased notably.

Biocontrol agents promote growth of potato pathogens, depending on environmental conditions

“…With the sole exception of extreme, obligate halophiles (water‐activity limits in the range 0.650 to 0.610; Stevenson et al ., ), the most xerotolerant bacteria can only grow, and retain metabolic activity, down to 0.850 to 0.800 water activity, depending on species, whereas some fungi can do so in the range 0.690 to 0.605 (Williams and Hallsworth, ; Stevenson et al ., ,b). Indeed, the structures of some fungi hold various records for tolerance to extreme biophysical conditions (Cray et al ., and references therein; Stevenson et al ., ,b; Wyatt et al ., ,b). It is, however, fortuitous that most plant pathogens are incapable of growth at ≤ 0.800 water activity (see below).…”

Ecology of aspergillosis: insights into the pathogenic potency of Aspergillus fumigatus and some other Aspergillus species

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Water structure and chaotropicity: their uses, abuses and biological implications

“…70,[73][74][75][76] At higher concentrations of chaotropic substances, environments become effectively sterile 75,76 because macromolecular systems are denatured and cells may lyse or become ''mummified''. 66,72,74,[78][79][80] They also utilize the inhibitory potency (and indeed lethality) of chaotropicity by producing an impressive arsenal of chaotropic and hydrophobic stressors as antimicrobials. 62 Microbes can preferentially utilize or accumulate chaotropic or kosmotropic metabolites depending on the prevailing environmental conditions.…”