Roles of Candida albicans Mig1 and Mig2 in glucose repression, pathogenicity traits, and SNF1 essentiality.

Metabolic adaptation is linked to the ability of the opportunistic pathogen Candida albicans to colonize and cause infection in diverse host tissues. One way that C. albicans controls its metabolism is through the glucose repression pathway, where expression of alternative carbon source utilization genes is repressed in the presence of its preferred carbon source, glucose. Here we carry out genetic and gene expression studies that identify transcription factors Mig1 and Mig2 as mediators of glucose repression in C. albicans. The well-studied Mig1/2 orthologs ScMig1/2 mediate glucose repression in the yeast Saccharomyces cerevisiae; our data argue that C. albicans Mig1/2 function similarly as repressors of alternative carbon source utilization genes. However, Mig1/2 functions have several distinctive features in C. albicans. First, Mig1 and Mig2 have more co-equal roles in gene regulation than their S. cerevisiae orthologs. Second, Mig1 is regulated at the level of protein accumulation, more akin to ScMig2 than ScMig1. Third, Mig1 and Mig2 are together required for a unique aspect of C. albicans biology, the expression of several pathogenicity traits. Such Mig1/2-dependent traits include the abilities to form hyphae and biofilm, tolerance of cell wall inhibitors, and ability to damage macrophage-like cells and human endothelial cells. Finally, Mig1 is required for a puzzling feature of C. albicans biology that is not shared with S. cerevisiae: the essentiality of the Snf1 protein kinase, a central eukaryotic carbon metabolism regulator. Our results integrate Mig1 and Mig2 into the C. albicans glucose repression pathway and illuminate connections among carbon control, pathogenicity, and Snf1 essentiality

Glucose-enhanced oxidative stress resistance-A protective anticipatory response that enhances the fitness of Candida albicans during systemic infection

Acknowledgments We thank Carol Munro for her generosity in providing the plasmids for barcoding C. albicans, and Victoria Brown, Gerry Fink, Bill Fonzi, Guanghua Huang, Joachim Morschauser, Suzanne Noble, Jesus Pla, Patrick Van Dijck, Reinhard Würzner and Oscar Zaragoza for providing strains. We thank our colleagues in the MRC Centre for Medical Mycology and the Aberdeen Fungal Group for insightful discussions. We are grateful to the following Research Facilities for their advice and support: the Centre for Genome Enabled Biology at the University of Aberdeen, and the Sequencing Facility at the University of Exeter for help with the barcode sequencing. Funding: This work was funded by a programme grant to AJPB, NARG, LEP and MGN from the UK Medical Research Council [www.mrc.ac.uk: MR/M026663/1, MR/M026663/2] and by PhD studentships to DEL from the Universities of Aberdeen and Exeter. The work was also supported by the Medical Research Council Centre for Medical Mycology (MR/N006364/1, MR/N006364/2). NARG acknowledges Wellcome support of Senior Investigator (101873/Z/13/Z, 224323/Z/21/Z) and Collaborative (200208/A/15/Z, 215599/Z/19/Z) Awards. MGN was supported by an ERC Advanced Grant (833247) and a Spinoza Grant of the Netherlands Organization for Scientific Research. The barcode sequencing performed by the Exeter Sequencing Facility utilised equipment funded by Wellcome (218247/Z/19/Z). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Nature of b-1,3-Glucan-Exposing Features on Candida albicans Cell Wall and Their Modulation

Funding Information: This work was supported by a programme grant from the UK Medical Research Council (MR/M026663/1; MR/M026663/2) and by the Medical Research Council Centre for Medical Mycology (MR/N006364/1; MR/N006364/2). NARG acknowledges Wellcome support for a Senior Investigator (101873/Z/13/Z), Collaborative (200208/A/15/Z; 215599/Z/19/Z) and Strategic Awards (097377/Z11/Z). MGN was supported by an ERC Advanced Grant (833247) and a Spinoza Grant of the Netherlands Organization for Scientific Research.Peer reviewedPublisher PD

Gene Function of the Transcription Factors Mig1, Mig2, and Zfu2 in Candida albicans

Candida albicans is a commensal fungus that can cause life-threatening illnesses for those that are immunocompromised, have had major surgery, or have in-dwelling medical devices. C. albicans lives on most mucosal surfaces in the body where it employs drasticallydifferent transcriptional patterns depending on which body site it inhabits, or whether it acts as a commensal or a pathogenic organism. The ability of C. albicans to alter itstranscriptional landscape to live in these diverse niches within the body is a testament to its genetic flexibility. This thesis will attempt to understand the functions of threedistinct transcription factors Mig1, Mig2, and Zfu2 that enable C. albicans to coordinate proper gene expression in vivo and in vitro. These transcription factors play distinct roles in controlling proper gene expression in two different contexts. Zfu2 may control gene expression in the context of in vivo biofilm formation, while Mig1 and Mig2 are repressors of alternative carbon source utilization genes and control cell wall integrity. All three of these transcription factors play a role in virulence and therefore are of importance to study

Impact of surface topography on biofilm formation by Candida albicans.

Candida albicans is a fungal pathogen that causes serious biofilm-based infections. Here we have asked whether surface topography may affect C. albicans biofilm formation. We tested biofilm growth of the prototypical wild-type strain SC5314 on a series of polydimethylsiloxane (PDMS) solids. The surfaces were prepared with monolayer coatings of monodisperse spherical silica particles that were fused together into a film using silica menisci. The surface topography was varied by varying the diameter of the silica particles that were used to form the film. Biofilm formation was observed to be a strong function of particle size. In the particle size range 4.0-8.0 μm, there was much more biofilm than in the size range 0.5-2.0 μm. The behavior of a clinical isolate from a clade separate from SC5314, strain p76067, showed results similar to that of SC5314. Our results suggest that topographic coatings may be a promising approach to reduce C. albicans biofilm infections

Scanning electron microscope (SEM) images of films fabricated from the 1, 2, 4, and 8 μm diameter silica spheres.

<p>The small bridges between the particles are evident in the images of the 4 and 8 μm particles. These bridges, together with similar bridges to the solid, stabilize the film so that it is unaffected by exposure to a stirred solution, rinsing etc.</p

Photographs of <i>C</i>. <i>albicans</i> grown in (RPMI) media for 24 hours, 37°C on test solids as indicated.

<p>Photographs of <i>C</i>. <i>albicans</i> grown in (RPMI) media for 24 hours, 37°C on test solids as indicated.</p

Atomic Force Microscope image of test surface consisting of 1 μm diameter silica spheres adhered to a PDMS solid.

<p>The entire sample is coated in a very thin layer of silica.</p

Bypass of <i>Candida albicans</i> Filamentation/Biofilm Regulators through Diminished Expression of Protein Kinase Cak1

<div><p>Biofilm formation on implanted medical devices is a major source of lethal invasive infection by <i>Candida albicans</i>. Filamentous growth of this fungus is tied to biofilm formation because many filamentation-associated genes are required for surface adherence. Cell cycle or cell growth defects can induce filamentation, but we have limited information about the coupling between filamentation and filamentation-associated gene expression after cell cycle/cell growth inhibition. Here we identified the CDK activating protein kinase Cak1 as a determinant of filamentation and filamentation-associated gene expression through a screen of mutations that diminish expression of protein kinase-related genes implicated in cell cycle/cell growth control. A <i>cak1</i> <u>d</u>iminished e<u>x</u>pression (DX) strain displays filamentous growth and expresses filamentation-associated genes in the absence of typical inducing signals. In a wild-type background, expression of filamentation-associated genes depends upon the transcription factors Bcr1, Brg1, Efg1, Tec1, and Ume6. In the <i>cak1</i> DX background, the dependence of filamentation-associated gene expression on each transcription factor is substantially relieved. The unexpected bypass of filamentation-associated gene expression activators has the functional consequence of enabling biofilm formation in the absence of Bcr1, Brg1, Tec1, Ume6, or in the absence of both Brg1 and Ume6. It also enables filamentous cell morphogenesis, though not biofilm formation, in the absence of Efg1. Because these transcription factors are known to have shared target genes, we suggest that cell cycle/cell growth limitation leads to activation of several transcription factors, thus relieving dependence on any one.</p></div