Aquaporin Expression and Freeze Tolerance in Candida albicans

Abstract

Aquaporins are members of the major intrinsic protein superfamily of integral membrane proteins which enable the transport of water, glycerol, and other solutes across membranes in various organisms. In microorganisms, the physiological role of aquaporins is not yet defined. We found a clear correlation between expression of the Candida albicans aquaporin-encoding gene AQY1 and freeze tolerance. A connection with the function for the aquaporin in the natural environment of C. albicans is, however, not obvious.Aquaporins are members of the major intrinsic protein (MIP) superfamily of integral membrane proteins (4, 23). They mediate water transport across cell membranes in numerous species (7). Mammalian and plant aquaporins have important functions in water homeostasis and osmoregulation (1,20), but the physiological function of microbial aquaporins remains a matter of debate (9,16,17,18,26,27). Transport processes that involve the uptake or efflux of water mediated by water channel proteins are nevertheless believed to be of major importance for microorganisms, particularly under conditions where the passive diffusion of water through the lipid bilayer is insufficient.In Saccharomyces cerevisiae, two aquaporin-encoding genes have been identified and characterized, AQY1 and AQY2 (6,11,21). Aquaporin expression is strongly correlated with freeze tolerance (28). Deletion of both aquaporin genes from a laboratory strain makes the cells more sensitive to freezing, and overexpression of the genes improves freeze tolerance (28). These findings are consistent with a role for plasma membrane water transport activity in determining freeze tolerance in S. cerevisiae.A functional water channel is known in Candida albicans (12), but a aquaporin null strain does not have a pronounced phenotype (12). Whereas an S. cerevisiae aquaporin null strain displays a small but significant decrease in sensitivity to osmotic shock (6), deletion of C. albicans AQY1 resulted in a far less pronounced phenotype (12). The minor effects of aquaporin deletion on cell surface hydrophobicity, flocculation, cell aggregation, and invasive growth observed in S. cerevisiae (11) were not noticeable in C. albicans (12).In this study, we determined whether the aquaporin-encoding gene AQY1 is a determinant of C. albicans freeze tolerance, as previously demonstrated for S. cerevisiae AQY1 and AQY2 (28). We verified the freeze-sensitive C. albicans AQY1 deletion phenotype, which is remedied by reintroduction of the gene. These findings strengthen the correlation between aquaporin function and freeze tolerance in microorganisms.We compared the freeze tolerance of heterozygous AQY1 deletion strain JC0186 (aqy1⌬/AQY1) (12) and homozygous AQY1 deletion strain JC0188 (aqy1⌬/aqy1⌬) (12). Both strains were grown overnight in 5 ml YPD (1% wt/vol yeast extract, 2% wt/vol Bactopeptone, 2% glucose) or uracil-deficient minimal medium (6.67 g/liter yeast nitrogen base without amino acids [Bio101, Qbiogene, France], 0.77 g/liter complete supplement mixture minus uracil [...

A novel dehydrin-like protein from Aspergillus fumigatus regulates freezing tolerance

“…Outflow of water through water channels, namely aquaporins, allows prompt restoration of the equilibrium (Soveral et al, 2006). A clear correlation was found between the expression of aquaporin genes and freeze tolerance in S. cerevisiae and Candida albicans (Tanghe et al, 2002(Tanghe et al, , 2005. Aquaporins are also known to be involved in the response to chilling injury of plants, and their heterologous overexpression enhanced freeze tolerance in yeasts (Li et al, 2008(Li et al, , 2009, indicating similar roles of aquaporins in yeasts and plants.…”

Identification of Genes Upregulated by the Transcription Factor Bcr1 That Are Involved in Impermeability, Impenetrability, and Drug Resistance of Candida albicans a/ α Biofilms

“…Therefore, although all five of these proteins have been shown to play roles in iron homeostasis, they may also play a direct role in the architecture of the matrix, which may be responsible for the vertical orientation of hyphae, biofilm thickness, impermeability, impenetrability, and drug resistance. Aqy1, an aquaporin water channel (44), is located in the plasma membrane (43) and has been shown to play a role in resistance to freeze-thawing (83). It has not previously been shown to play a role in biofilm development.…”

Fungal aquaporins: cellular functions and ecophysiological perspectives

“…Deletion of orthodox AQP in laboratory strains of S. cerevisiae (Tanghe et al 2002) and C. albicans (Tanghe et al 2005a) made cells sensitive to freezing, while overexpression of Aqy2 improved freeze tolerance (Tanghe et al 2002(Tanghe et al , 2005b. Tanghe et al (2006) supposed that in aqueous solution, extracellular water freezes faster than intracellular because of the higher osmolarity of the intracellular content.…”