To successfully colonize the vaginal tract Candida glabrata has to cope with
various stresses including the presence of acetic acid at a low pH that is produced
by the bacteria that co-colonize this niche. The genes/pathways involved in C.
glabrata tolerance and response to acetic acid are largely unknown, although
these are a highly interesting set of novel targets to control vaginal infections
caused by this yeast. Saccharomyces cerevisae response and tolerance to acetic
acid was found to be largely mediated by the ScHaa1 transcription factor [1,2,3].
In this work the involvement of CgHaa1 in C. glabrata tolerance and response to
acetic acid is demonstrated. Elimination of CgHAA1 gene from C. glabrata
genome dramatically increased susceptibility of this pathogenic yeast to acetic
acid (30 mM at pH 4.0). Around 140 genes were found to be up-regulated,
directly or indirectly, by CgHaa1 in response to acetic acid stress, based on results of a transcriptomic analysis. Functional clustering of the genes activated
by CgHaa1 under acetic acid stress shows an enrichment of those involved in
carbohydrate metabolism, transport, cell wall maintenance, regulation of internal
pH and nucleic acid processing. At least five of the CgHaa1-regulated genes were
found to increase C. glabrata tolerance to acetic acid including CgGAD1,
encoding a glutamate decarboxylase; CgTPO2/3, encoding a drug efflux pump of
the Major Facilitator Superfamily; CgYPS1, encoding a cell wall aspartyl
protease; and CAGL0H04851 and CAGL0E03740, encoding two uncharacterized
ORFs. Altogether our results are consistent with the concept that the CgHaa1-
signalling pathway increases C. glabrata tolerance to acetic acid by reducing the
internal accumulation of the acid and by up-regulating the activity of the plasma
membrane proton pump H+-ATPase CgPma1, two essential features for a robust
weak acid response.
The role exerted by CgHaa1 in the ability of C. glabrata to colonize
reconstituted vaginal human epithelium (RVHE) in the presence of acetic acid
(30 mM at pH 4.0) was also investigated in this work. In the absence of acetic
acid wild-type and DCgHaa1 mutant cells were able to colonize RVHE at a
similar rate, however, in the presence of acetic acid colonization of the vaginal
tissue was markedly reduced in the mutant background. The reduced colonizing
capacity of DCgHaa1 mutant cells was correlated with a reduced expression of
the adhesin-encoding genes EPA6, EPA7 and EPA1 and with a lower
adhesiveness to the extracellular matrix proteins fibronectin and vitronectin
