Water Relations of Xerophilic Fungi Isolated from Prunes

Abstract

The predominant spoilage fungi of dried and high-moisture prunes were members of the Aspergillus glaucus group and Xeromyces bisporus. Chrysosporium spp. were also important. At the mean pH of prune flesh (3.8) and at 25 C, X. bisporus grew at water activities (a,) down to 0.605, and Chrysosporium fastidium grew to 0.686. Germination was always followed by growth, but within the 120-day incubation period, the mninimum aw permitting asexual sporulation was usually higher than that permitting germination. Sexual sporulation often required an even higher aw. The water requirements of aspergilli were appreciably greater at this pH than near neutrality, no species germinating below 0.738 aw. This was probably a consequence of a high spore-death rate during incubation at low aw and pH.

Microbiology of sugar‐rich environments: diversity, ecology and system constraints

“…The vast majority of microbial species on Earth are incapable of growth or metabolic activity below a water activity of 0.90 (Brown, 1990;Manzoni et al, 2012;Moyano et al, 2012;2013;Stevenson and Hallsworth, 2014), which is equivalent to ∼2.2 M (∼75% w/v) sucrose or ∼3.1 M (∼56% w/v) glucose at 25°C. Nevertheless, several xerophilic yeasts and fungi are capable of cell division at water activities in the range of 0.70-0.60 (Pitt and Christian, 1968;Williams and Hallsworth, 2009; Scott, 1953), and Streptomyces albidoflavus (0.895) (Stevenson and Hallsworth, 2014). Whereas the peculiar adaptations of halophiles have been well characterized (Oren, 2013;Oren and Hallsworth, 2014), the relatively feeble cell biology of sugar-tolerant species at low water activity is not yet fully understood.…”

Water and temperature relations of soil Actinobacteria

“…Throughout the past 50 years of microbiological research, the established water-activity windows for cell division of xerophiles have remained unchanged (Pitt and Christian, 1968;Brown, 1976;1990;Grant, 2004;Stevenson et al, 2014) despite the recent interest in habitability of hostile environments in relation to searches for life beyond the Earth (Marion and Kargel, 2008;Kminek et al, 2010;Harrison et al, 2013;Stevenson et al, 2014 . For any data that can provide definitive evidence for microbial cell division at water activities significantly below 0.605, the potential implications would be manifold.…”

Multiplication of microbes below 0.690 water activity: implications for terrestrial and extraterrestrial life

“…5 Some reports have alluded to the possibility of microbial growth and metabolism at the otherwise unprecedented water-activity values of 0.382 (for deep-sea halophiles in MgCl2-saturated brine; van der Wielen et al, 2005), < 0.450 (for halophiles in the CaCl2-rich, Antarctic Don Juan Pond; Siegel et al, 1979), 0.500 (Actinobacteria isolated from algal mats and cultured in soil-based substrates; Doroshenko et al, 2005;Doroshenko et al, 2006;Zvyagintsev et al, 2009;Zvyagintsev et al, 2012), 0.570 (for halophiles in acidic, saline lakes; Mormile et al, 2009), 0.600 [for germination of Wallemia sebi (a xerophilic basidiomycete) on high-sugar substrates; Frank and Hess, 1941] and 0.600 [reported value for optimum growth of halophiles (Jaenicke and Bohm, 1998), and biotic activity in salt lakes (Cobucci-Ponzano et al, 2006)]. Some of these values were hypothetical (see below), and the other claims have not been accepted or have been refuted by authors of a number of subsequent studies (Pitt and Christian, 1968;Wynn-Williams, 1996;Beaty et al, 2006;Hallsworth et al, 2007;Kminek et al, 2010;Oren, 2011;Stevenson and Hallsworth, 2014 E. Hallsworth, submitted). 6 The Don Juan Pond (located within the McMurdo Dry Valleys, Antarctica) is a CaCl2saturated brine pool situated in a closed basin and fed by seasonal meltwater streams and deliquescent seepages, both of which are thought to deliver CaCl2 to the lake (Dickson et al, 2013).…”

“…Proposed limits of 0.570 or 0.600 aw for biotic activity of halophiles were speculative (i.e. not derived from determinations of water activity; Jaenicke and Bohm, 1998;Mormile et al, 2009;Cobucci-Ponzano et al, 2006), and likely sources of experimental error in studies of W. sebi germination have been discussed previously (Pitt and Christian, 1968). Furthermore, multiplication of microbes in terrestrial brine lakes which can reach values below 0.600 aw may have actually occurred at higher wateractivity values that resulted from seasonal and weatherrelated fluctuations in salt concentration (Oren, 1988;1993;Cobucci-Ponzano et al, 2006;Mormile et al, 2009).…”