Chaophilic or chaotolerant fungi: a new category of extremophiles?

Abstract

It is well known that few halophilic bacteria and archaea as well as certain fungi can grow at the highest concentrations of NaCl. However, data about possible life at extremely high concentrations of various others kosmotropic (stabilizing; like NaCl, KCl, and MgSO4) and chaotropic (destabilizing) salts (NaBr, MgCl2, and CaCl2) are scarce for prokaryotes and almost absent for the eukaryotic domain including fungi. Fungi from diverse (extreme) environments were tested for their ability to grow at the highest concentrations of kosmotropic and chaotropic salts ever recorded to support life. The majority of fungi showed preference for relatively high concentrations of kosmotropes. However, our study revealed the outstanding tolerance of several fungi to high concentrations of MgCl2 (up to 2.1 M) or CaCl2 (up to 2.0 M) without compensating kosmotropic salts. Few species, for instance Hortaea werneckii, Eurotium amstelodami, Eurotium chevalieri and Wallemia ichthyophaga, are able to thrive in media with the highest salinities of all salts (except for CaCl2 in the case of W. ichthyophaga). The upper concentration of MgCl2 to support fungal life in the absence of kosmotropes (2.1 M) is much higher than previously determined to be the upper limit for microbial growth (1.26 M). No fungal representatives showed exclusive preference for only chaotropic salts (being obligate chaophiles). Nevertheless, our study expands the knowledge of possible active life by a diverse set of fungi in biologically detrimental chaotropic environments.

Production of Secondary Metabolites in Extreme Environments: Food- and Airborne Wallemia spp. Produce Toxic Metabolites at Hypersaline Conditions

“…muriae can grow at MgCl 2 concentrations of up to 11%-17%, while W . ichthyophaga can grow even up to 20% MgCl 2 [23, 24, 72]. Addition of the chaotropic MgCl 2 as solute to the growth media resulted either in very small production of secondary metabolites or even their complete absence.…”

Halotolerance (ionic NaCl) and chaotolerance (ionic MgCl2) of the human pathogen Wallemia mellicola isolated, for the first time, from indoor air in Poland

“…Extensive studies have identified fungi that thrive on media with NaCl. In contrast, few strains are able to growth in the presence of MgCl 2 [19].…”

“…4). According to Zajc et al [19], the type of salt added to media affects the growth of strains. Extensive studies have identified fungi that thrive on media with NaCl.…”

Nature Abhors a Vacuum: Highly Diverse Mechanisms Enable Spoilage Fungi to Disperse, Survive, and Propagate in Commercially Processed and Preserved Foods

“…Alternatively, halotolerance refers to growth capacity in highly saline environments, and osmotolerance refers to resistance to osmotic pressure, that is, salts or sugars (Pitt, 1975;Pitt & Hocking, 1997). It is noteworthy that certain solutes, termed chaotropic, are more inhibitory than other kosmotropic solutes, because they destabilize macromolecules (Lievens et al, 2014;Zajc et al, 2014).…”

“…One common solute, glycerol, is produced by the well-studied high osmolarity glycerol (HOG) pathway. The HOG pathways are initiated in response to NaCl changes, producing or expelling glycerol as needed to survive osmotic stress (Gostinčar et al, 2014;Plemenitaš et al, 2014;Zajc et al, 2014).…”