Does Candida albicans Als5p Amyloid Play a Role in Commensalism in Caenorhabditis elegans?

Candida albicans , a dimorphic fungus and an opportunistic pathogen, possesses a myriad of adherence factors, including members of the agglutinin-like sequence (Als) family of mannoproteins. The adhesin Als5p mediates adhesion to many substrates and is upregulated during commensal interactions but is downregulated during activeC. albicans infections. An amyloid-forming core sequence at residues 325 to 331 is important for Als5p function, because a single-amino-acid substitution at position 326 (V326N) greatly reduces Als5p-mediated adherence. We evaluated the role of Als5p in host-microbe interactions by usingCaenorhabditis elegans nematodes as a host model and feeding themSaccharomyces cerevisiae expressing Als5p on the surface. Als5p-expressing yeast had 8.5- and 3.5-fold-increased intestinal accumulation rates compared to Als5p-nonexpressingS. cerevisiae or yeast expressing amyloid-deficient Als5pV326N , respectively. Surprisingly, this accumulation delayedS. cerevisiae -induced killing ofC. elegans. The median survival time was nearly twice as long as that of nematodes fed nonexpressing or non-amyloid-forming Als5pV326N -expressingS. cerevisiae . Treatment with the amyloid-inhibiting dye Congo red or repression of Als5p expression abrogated the protective effect of Als5p. Furthermore, Als5p had no effect on oocyte quantity or quality, since nematodes fed either empty vector (EV)- or Als5pV326N -expressingS. cerevisiae had similar egg-laying and egg-hatching rates. This study is the first, to our knowledge, to show that expression of an amyloid-forming protein can attenuate pathogenicity inC. elegans .