Candida auris is an emerging multidrug-resistant fungal pathogen and a new global threat to human health. A unique morphological feature of this fungus is its multicellular aggregating phenotype, which has been thought to be associated with defects in cell division. In this study, we report a new aggregating form of two clinical C. auris isolates with increased biofilm forming capacity due to enhanced adherence of adjacent cells and surfaces. Unlike the previously reported aggregating morphology, this new aggregating multicellular form of C. auris can become unicellular after treatment with proteinase K or trypsin. Genomic analysis demonstrated that amplification of the subtelomeric adhesin gene ALS4 is the reason behind the strain’s enhanced adherence and biofilm forming capacities. Many clinical isolates of C. auris have variable copy numbers of ALS4, suggesting that this subtelomeric region exhibits instability. Global transcriptional profiling and quantitative real-time PCR assays indicated that genomic amplification of ALS4 results in a dramatic increase in overall levels of transcription. Compared to the previously characterized nonaggregative/yeast-form and aggregative-form strains of C. auris, this new Als4-mediated aggregative-form strain of C. auris displays several unique characteristics in terms of its biofilm formation, surface colonization, and virulence.

Morphological transitions and metabolic regulation are critical for the human fungal pathogen Candida albicans to adapt to the changing host environment. In this study, we generated a library of central metabolic pathway mutants in the tricarboxylic acid (TCA) cycle, and investigated the functional consequences of these gene deletions on C. albicans biology. Inactivation of the TCA cycle impairs the ability of C. albicans to utilize non-fermentable carbon sources and dramatically attenuates cell growth rates under several culture conditions. By integrating the Ras1-cAMP signaling pathway and the heat shock factor-type transcription regulator Sfl2, we found that the TCA cycle plays fundamental roles in the regulation of CO 2 sensing and hyphal development. The TCA cycle and cAMP signaling pathways coordinately regulate hyphal growth through the molecular linkers ATP and CO 2 . Inactivation of the TCA cycle leads to lowered intracellular ATP and cAMP levels and thus affects the activation of the Ras1-regulated cAMP signaling pathway. In turn, the Ras1-cAMP signaling pathway controls the TCA cycle through both Efg1-and Sfl2-mediated transcriptional regulation in response to elevated CO 2 levels. The protein kinase A (PKA) catalytic subunit Tpk1, but not Tpk2, may play a major role in this regulation. Sfl2 specifically binds to several TCA cycle and hypha-associated genes under high CO 2 conditions. Global transcriptional profiling experiments indicate that Sfl2 is indeed required for the gene expression changes occurring in response to these elevated CO 2 levels. Our study reveals the regulatory role of the TCA cycle in CO 2 sensing and hyphal development and establishes a novel link between the TCA cycle and Ras1-cAMP signaling pathways. Author summaryEnergy metabolism through the TCA cycle and mitochondrial electron transport are critical for the human fungal pathogen Candida albicans to survive and propagate in the host. Data Availability Statement:The RNA-seq dataset has been deposited into the NCBI Gene Expression Omnibus (GEO) portal (accession# GSE102039).Funding: This work was supported by grants from the Chinese National Natural Science Foundation (31625002 and 31370175 to GH and 31570139 to LT). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. This is, in part, due to the fact that C. albicans is a Crabtree-negative species, and thus exclusively uses respiration when oxygen is available. Here, we investigate the roles of the TCA cycle in hyphal development and CO 2 sensing in C. albicans. Through the use of ATP and the cellular signaling molecule CO 2 , the TCA cycle integrates with the Ras1-cAMP signaling pathway, which is a central regulator of hyphal growth, to govern basic cellular biological processes. Together with Efg1, a downstream transcription factor of the cAMP signaling pathway, the heat shock factor-type transcription regulator Sfl2 controls CO 2 -induced hyphal growth in C. albicans. Deletion of SFL2 result...