Search

Candida albicans is a fungal component of the human gut microbiota and an opportunistic pathogen. C. albicans transcription factors (TFs), Wor1 and Efg1, are master regulators of an epigenetic switch required for fungal mating that also control colonization of the mammalian gut. We show that additional mating regulators, WOR2, WOR3, WOR4, AHR1, CZF1, and SSN6, also influence gut commensalism. Using Calling Card-seq to record Candida TF DNA-binding events in the host, we examine the role and relationships of these regulators during murine gut colonization. By comparing in-host transcriptomes of regulatory mutants with enhanced versus diminished commensal fitness, we also identify a set of candidate commensalism effectors. These include Cht2, a GPI-linked chitinase whose gene is bound by Wor1, Czf1, and Efg1 in vivo, that we show promotes commensalism. Thus, the network required for a C. albicans sexual switch is biochemically active in the host intestine and repurposed to direct commensalism.

Eukaryotes have evolved elaborate mechanisms to ensure that chromosomes segregate with high fidelity during mitosis and meiosis, and yet specific aneuploidies can be adaptive during environmental stress. Here, we identify a chromatin-based system required for inducible aneuploidy in a human pathogen. Candida albicans utilizes chromosome missegregation to acquire tolerance to antifungal drugs and for nonmeiotic ploidy reduction after mating. We discovered that the ancestor of C. albicans and 2 related pathogens evolved a variant of histone 2A (H2A) that lacks the conserved phosphorylation site for kinetochore-associated Bub1 kinase, a key regulator of chromosome segregation. Using engineered strains, we show that the relative gene dosage of this variant versus canonical H2A controls the fidelity of chromosome segregation and the rate of acquisition of tolerance to antifungal drugs via aneuploidy. Furthermore, whole-genome chromatin precipitation analysis reveals that Centromere Protein A/ Centromeric Histone H3-like Protein (CENP-A/Cse4), a centromeric histone H3 variant that forms the platform of the eukaryotic kinetochore, is depleted from tetraploid-mating products relative to diploid parents and is virtually eliminated from cells exposed to aneuploidy-promoting cues. We conclude that genetically programmed and environmentally induced changes in chromatin can confer the capacity for enhanced evolvability via chromosome missegregation.

Gene transfer agents ( GTAs) are genetic exchange elements that resemble small DNA bacteriophages that transfer random pieces of the producing cell's genome to recipient cells. The best-studied GTA is that of R hodobacter capsulatus, termed RcGTA. We discovered that the putative response regulator CtrA, which is essential for RcGTA production, is required for RcGTA-mediated gene acquisition, and confirmed that a RecA homologue is required. It was also discovered that a DprA ( DNA-protecting protein A) homologue is essential for RcGTA-mediated gene acquisition, and that dprA expression is induced by gtaI-dependent quorum-sensing and non-phosphorylated CtrA. Modelling of the R . capsulatus DprA structure indicated the presence of a C-terminal region that resembles a dsDNA-binding protein domain. Purified His-tagged R . capsulatus DprA protein bound to both single-stranded (ss) DNA and double-stranded (ds) DNA, but with a greater affinity for ssDNA. Additionally, DprA protected dsDNA from endonuclease digestion, and increased the rate of nucleation of E scherichia coli RecA onto ssDNA. Single-cell expression analyses revealed that dprA is expressed in the majority of cells throughout a population. Overall, the results suggest that incorporation of RcGTA DNA into the recipient cell genome proceeds through a homologous recombination pathway resembling DNA recombination in natural transformation. [ABSTRACT FROM AUTHOR]