Salt stress and plasma-membrane fluidity in selected extremophilic yeasts and yeast-like fungi

Abstract

We have investigated changes in plasma-membrane fluidity in relation to NaCl concentrations in yeasts and yeast-like fungi that were isolated from either subglacial ice or hypersaline waters. In both of these natural environments, these organisms are exposed to low water activity, due to either high NaCl concentrations or low temperatures. Our data indicate that the fluidity of the plasma membrane can be used as an indicator of fitness for survival in extreme environments. Fungi that can survive in such extreme environments, such as Hortaea werneckii in the hypersaline waters of salterns, and Cryptococcus liquefaciens in subglacial environments, showed similar profiles of plasma-membrane fluidity in response to raised salinity. The same was seen for ubiquitous fungi, which are generally adapted for different types of stress, such as Aureobasidium pullulans and Rhodotorula mucilaginosa. Representatives of both of these groups modulated their plasma-membrane fluidity differently. When salinity exceeded their optimal range, the ubiquitous stress-tolerant species (A. pullulans, Rh. mucilaginosa) showed increased plasma-membrane fluidity, whereas in the dominant extremophiles (H. werneckii, Cr. liquefaciens), it decreased. On the other hand, the plasma membranes of the fungi with a narrow ecological amplitude (Arctic A. pullulans and Rhodosporium diobovatum) showed different responses.

Evolution of Fungal Pathogens in Domestic Environments?

“…Its ability to survive in hypersaline (Gunde-Cimerman et al 2000), acidic and basic (Ranta 1990;Shiomi et al 2004), and cold and oligotrophic (Onofri 1999) environments is possible because of several molecular adaptations (Gostin car et al 2008;Kogej et al 2006;Kogej et al 2005;Turk et al 2007) and of their rapid dimorphic switching from small colourless yeast cells to thick-walled, heavily melanised, meristematic forms (Bermejo et al 1981). Due to its traits, A. pullulans has recently been proposed as a model for investigating fungal phenotypic plasticity (Slepecky & Starmer 2009).…”

Identification and characterization of putative osmosensors, HwSho1A and HwSho1B, from the extremely halotolerant black yeast Hortaea werneckii

“…The most relevant differences for H. werneckii that have been studied to date relate to its plasmamembrane properties (Turk et al, 2007), osmolyte composition (Petrovic et al, 2002), accumulation of ions (Kogej et al, 2005), melanization of the cell wall (Kogej et al, 2006), and differential expression of osmo-responsive genes (Vaupotic and Plemenitas, 2007). The existence of a signaling pathway that is similar to the S. cerevisiae HOG pathway was demonstrated by identification of the putative histidine-kinase-like osmosensor HwHhk7 (Lenassi and Plemenitas, 2007), together with two MAPKs: MAPKK HwPbs2 (our unpublished data) and the final MAPK HwHog1 Turk and Plemenitas, 2002).…”

Plasma membrane composition of Debaryomyces hansenii adapts to changes in pH and external salinity

“…More recently, the effect of salt on plasma membrane fluidity has been studied in some selected extremophilic yeasts and yeast-like fungi. When salinity exceeded their optimal range, the ubiquitous stresstolerant species (A. pullulans, Rhodotorula mucilaginosa), generally adapted for different types of stress, showed increased plasma-membrane fluidity, while in the dominant extremophiles (H. werneckii, Cryptococcus liquefaciens), it decreased (Turk et al, 2007).…”