Fungal Xerophiles (Osmophiles)


Xerophilic fungi are yeasts and moulds that are capable of growth at or below a water activity (aw) of 0.85. These microorganisms have developed physiological mechanisms that enable their biochemical pathways to function in environments where little water is available. External conditions of low aw are sensed by membrane osmosensors, and xerophiles then accumulate glycerol as a compatible solute to balance the internal and external osmotic pressure. They also modify their membranes to retain this glycerol within the cell. As a group, xerophiles are extremely important in the spoilage of many processed foods and stored commodities, and in indoor environments. Moderate xerophiles include species within Aspergillus, Penicillium and Eurotium. Extreme xerophiles compete poorly at high aw, because they require decreased aw for growth. Some xerophiles have a preference for salt or sugar substrates, whereas other species can be isolated from both jam and salterns. Xerophiles are widely spread on the fungal tree of life.

Key Concepts:

  • Xerophiles have requirement for reduced water activity; fungi are the most successful xerophilic organisms, and the most extreme xerophiles are found among fungi.

  • Compatible solutes are accumulated intracellularly to maintain the osmotic balance in response to decreased water availability.

  • Glycerol is the primary compatible solute among xerophilic fungi.

  • Membrane composition plays an important role in retaining glycerol within the cells of xerophiles.

  • Moderate xerophiles of the genera Aspergillus, Eurotium and Penicillium are economically important spoilage organisms.

  • Some xerophiles are isolated from both high‐salt and high‐sugar environments; others have a preference for either salt or sugar.

  • Xerophiles can cause spoilage of food and feed: stored commodities, sugary products and salted foods.

  • Xerophilic species are widely spread on the fungal tree of life.

Keywords: xerophilic fungi; water activity; osmophiles; yeasts; food spoilage; extremophiles; glycerol; membrane permeability; compatible solutes

Figure 1.

Eurotium chevalieri, a xerophilic species occurring commonly in stored products. (a) Aspergillus head. Bar, 20 μm. (b) Ascospores showing equatorial crests typical of this species. Bar, 10 μm.

Figure 2.

Some less common extreme xerophiles found in foods. (a) Aleurioconidia of Chrysosporium farinicola, the anamorphic form of Bettsia alvei. Bar, 20 μm. (b) Cleistothecia and ascospores of Be. alvei. Bar, 50 μm. (c) Aleurioconidia and arthroconidia of Chrysosporium xerophilum. Bar, 20 μm. (d) Asci and ascospores of Eremascus albus, a rare species which is occasionally isolated from mustard powder. Bar, 20 μm.

Figure 3.

Two highly specialised xerophilic fungi. (a) Polyphialides of Polypaecilum pisce, a halophilic xerophile associated with dried salted fish. Bar, 20 μm. (b) Cleistothecium and ascospores of Xeromyces bisporus, the most xerophilic fungus known. Bar, 20 μm.



Andrews S and Pitt JI (1987) Further studies on the water relations of xerophilic fungi, including some halophiles. Journal of General Microbiology 133: 233–238.

Brown AD and Simpson JR (1972) Water relations of sugar‐tolerant yeasts: the role of intracellular polyols. Journal of General Microbiology 72: 589–591.

Butinar L, Zalar P, Frisvad JC and Gunde‐Cimerman N (2005) The genus Eurotium – members of indigenous fungal community in hypersaline waters of salterns. FEMS Microbiology Ecology 51: 155–166.

Frisvad JC, Smedsgaard J, Samson RA, Larsen TO and Thrane U (2007) Fumonisin B2 Production by Aspergillus niger. Journal of Agricultural and Food Chemistry 55: 9727–9732.

Gostinčar C, Grube M, de Hoog S, Zalar P and Gunde‐Cimerman N (2010) Extremotolerance in fungi: evolution on the edge. FEMS Microbiology Ecology 71: 2–11.

Gostinčar C, Turk M, Plemenitaš A and Gunde‐Cimerman N (2009) The expressions of Δ9‐,Δ12‐desaturases and an elongase by the extremely halotolerant black yeast Hortaea werneckii are salt dependent. FEMS Yeast Research 9: 247–256.

Hocking AD (1993) Responses of xerophilic fungi to changes in water activity. In: Jennings DH (ed.) Stress Tolerance of Fungi, pp. 233–256. New York: Marcel Dekker.

Hocking AD and Pitt JI (1979) Water relations of some Penicillium species at 25°C. Transactions of the British Mycological Society 73: 141–145.

Kinderlerer JL and Kellard B (1984) Ketonic rancidity in coconut due to xerophilic fungi. Phytochemistry 23: 2847–2849.

Leong SL, Vinnere Pettersson O, Rice T, Hocking AD and Schnürer J (2011) The extreme xerophilic mould Xeromyces bisporus – growth and competition at various water activities. International Journal of Food Microbiology 145: 57–63.

Magan N (1997) Fungi in extreme environments. In: Wicklow DT and Soderstrom B (eds) The Mycota IV, Environmental and Microbial Relationships, pp. 83–103. Berlin: Springer‐Verlag.

Peterson SW (2008) Phylogenetic analysis of Aspergillus species using DNA sequences from four loci. Mycologia 100: 205–226.

Pitt JI (1975) Xerophilic fungi and the spoilage of foods of plant origin. In: Duckworth RD (ed.) Water Relations of Foods, pp. 273–307. London: Academic Press.

Pitt JI and Hocking AD (2009) Fungi and Food Spoilage, 3rd edn. New York: Springer.

Pribylova L, de Montigny J and Sychrova H (2007) Osmoresistant yeast Zygosaccharomyces rouxii: the two most studied wild‐type strains (ATCC 2623 and ATCC 4291) differ in osmotolerance and glycerol metabolism. Yeast 24: 171–180.

Salazar M, Vongsangnak W, Panagiotou G, Andersen MR and Nielsen J (2009) Uncovering transcriptional regulation of glycerol metabolism in Aspergilli through genome‐wide gene expression data analysis. Molecular Genetics and Genomics 282: 571–586.

Turk M, Méjanelle L, Šentjurc M et al. (2004) Salt‐induced changes in lipid composition and membrane fluidity of halophilic yeast‐like melanized fungi. Extremophiles 8: 53–61.

Vinnere Pettersson O, Leong SL, Lantz H et al. (in press) Phylogeny and intraspecific variation of the extreme xerophile, Xeromyces bisporus.

Wheeler KA, Hocking AD, Pitt JI and Anggawati A (1986) Fungi associated with Indonesian dried fish. Food Microbiology 3: 351–357.

Zalar P, de Hoog GS, Schroers H‐J, Frank JM and Gunde‐Cimerman N (2005) Taxonomy and phylogeny of the xerophilic genus Wallemia (Wallemiomycetes and Wallemiales, cl. et ord. nov.). Antonie van Leeuwenhoek 87: 311–328.

Further Reading

Williams JP and Hallsworth JE (2009) Limits of life in hostile environments: no barriers to biosphere function? Environmental Microbiology 11: 3292–3308.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Vinnere Pettersson, Olga, and Leong, Su‐lin L(Aug 2011) Fungal Xerophiles (Osmophiles). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000376.pub2]