The Candida albicans Exocyst Subunit Sec6 Contributes to Cell Wall Integrity and Is a Determinant of Hyphal Branching

ABSTRACTThe yeast exocyst is a multiprotein complex comprised of eight subunits (Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84) which orchestrates trafficking of exocytic vesicles to specific docking sites on the plasma membrane during polarized secretion. To studySEC6function inCandida albicans, we generated a conditional mutant strain in whichSEC6was placed under the control of a tetracycline-regulated promoter. In the repressed state, the tetR-SEC6mutant strain (denoted tSEC6) was viable for up to 27 h; thus, all phenotypic analyses were performed at 24 h or earlier. Strain tSEC6 under repressing conditions had readily apparent defects in cytokinesis and endocytosis and accumulated both post-Golgi apparatus secretory vesicles and structures suggestive of late endosomes. Strain tSEC6 was markedly defective in secretion of aspartyl proteases and lipases as well as filamentation under repressing conditions. Lack ofSEC6expression resulted in markedly reduced lateral hyphal branching, which requires the establishment of a new axis of polarized secretion. Aberrant localization of chitin at the septum and increased resistance to zymolyase activity were observed, suggesting thatC. albicansSec6 plays an important role in mediating trafficking and delivery of cell wall components. The tSEC6 mutant was also markedly defective in macrophage killing, indicating a role ofSEC6inC. albicansvirulence. Taken together, these studies indicate that the late secretory protein Sec6 is required for polarized secretion, hyphal morphogenesis, and the pathogenesis ofC. albicans.

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Functional Analysis of the Exocyst Subunit Sec15 in Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00147-15 ◽

2015 ◽

Vol 14 (12) ◽

pp. 1228-1239 ◽

Cited By ~ 5

Author(s):

Alba A. Chavez-Dozal ◽

Stella M. Bernardo ◽

Hallie S. Rane ◽

Samuel A. Lee

Keyword(s):

Candida Albicans ◽

Gene Repression ◽

Content Type ◽

Polarized Secretion ◽

Conditional Mutant ◽

Direct Contrast ◽

Increased Sensitivity ◽

Gfp Marking ◽

Time Point

ABSTRACTIn prior studies of exocyst-mediated late secretion inCandida albicans, we have determined that Sec6 contributes to cell wall integrity, secretion, and filamentation. A conditional mutant lackingSEC6expression exhibits markedly reduced lateral hyphal branching. In addition, lack of the related t-SNAREs Sso2 and Sec9 also leads to defects in secretion and filamentation. To further understand the role of the exocyst in the fundamental processes of polarized secretion and filamentation inC. albicans, we studied the exocyst subunit Sec15. SinceSaccharomyces cerevisiae SEC15is essential for viability, we generated aC. albicansconditional mutant strain in whichSEC15was placed under the control of a tetracycline-regulated promoter. In the repressed state, cell death occurred after 5 h in the tetR-SEC15 strain. Prior to this time point, the tetR-SEC15 mutant was markedly defective in Sap and lipase secretion and demonstrated increased sensitivity to Zymolyase and chitinase. Notably, tetR-SEC15 mutant hyphae were characterized by a hyperbranching phenotype, in direct contrast to strain tetR-SEC6, which had minimal lateral branching. We further studied the localization of the Spitzenkörper, polarisomes, and exocysts in the tetR-SEC15 and tetR-SEC6 mutants during filamentation. Mlc1-GFP (marking the Spitzenkörper), Spa2-GFP (the polarisome), and Exo70-GFP (exocyst) localizations were normal in the tetR-SEC6 mutant, whereas these structures were mislocalized in the tetR-SEC15 mutant. Following alleviation of gene repression by removing doxycycline, first Spitzenkörper, then polarisome, and finally exocyst localizations were recovered sequentially. These results indicate that the exocyst subunits Sec15 and Sec6 have distinct roles in mediating polarized secretion and filamentation inC. albicans.

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Masking of β(1-3)-Glucan in the Cell Wall of Candida albicans from Detection by Innate Immune Cells Depends on Phosphatidylserine

Infection and Immunity ◽

10.1128/iai.01612-14 ◽

2014 ◽

Vol 82 (10) ◽

pp. 4405-4413 ◽

Cited By ~ 32

Author(s):

Sarah E. Davis ◽

Alex Hopke ◽

Steven C. Minkin ◽

Anthony E. Montedonico ◽

Robert T. Wheeler ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

De Novo ◽

Invasive Disease ◽

Innate Immune ◽

Dependent Manner ◽

Content Type ◽

Immune Effector ◽

Host Interactions ◽

Innate Immune Effector

ABSTRACTThe virulence ofCandida albicansin a mouse model of invasive candidiasis is dependent on the phospholipids phosphatidylserine (PS) and phosphatidylethanolamine (PE). Disruption of the PS synthase geneCHO1(i.e.,cho1Δ/Δ) eliminates PS and blocks thede novopathway for PE biosynthesis. In addition, thecho1Δ/Δ mutant's ability to cause invasive disease is severely compromised. Thecho1Δ/Δ mutant also exhibits cell wall defects, and in this study, it was determined that loss of PS results in decreased masking of cell wall β(1-3)-glucan from the immune system. In wild-typeC. albicans, the outer mannan layer of the wall masks the inner layer of β(1-3)-glucan from exposure and detection by innate immune effector molecules like the C-type signaling lectin Dectin-1, which is found on macrophages, neutrophils, and dendritic cells. Thecho1Δ/Δ mutant exhibits increases in exposure of β(1-3)-glucan, which leads to greater binding by Dectin-1 in both yeast and hyphal forms. The unmasking of β(1-3)-glucan also results in increased elicitation of TNF-α from macrophages in a Dectin-1-dependent manner. The role of phospholipids in fungal pathogenesis is an emerging field, and this is the first study showing that loss of PS inC. albicansresults in decreased masking of β(1-3)-glucan, which may contribute to our understanding of fungus-host interactions.

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Cell Wall-Related Bionumbers and Bioestimates of Saccharomyces cerevisiae and Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00250-13 ◽

2013 ◽

Vol 13 (1) ◽

pp. 2-9 ◽

Cited By ~ 58

Author(s):

Frans M. Klis ◽

Chris G. de Koster ◽

Stanley Brul

Keyword(s):

Saccharomyces Cerevisiae ◽

Cell Wall ◽

Candida Albicans ◽

Cell Size ◽

Pathogenic Fungus ◽

Turgor Pressure ◽

Hyphal Growth ◽

Biological Research ◽

Content Type ◽

Starting Point

ABSTRACTBionumbers and bioestimates are valuable tools in biological research. Here we focus on cell wall-related bionumbers and bioestimates of the budding yeastSaccharomyces cerevisiaeand the polymorphic, pathogenic fungusCandida albicans. We discuss the linear relationship between cell size and cell ploidy, the correlation between cell size and specific growth rate, the effect of turgor pressure on cell size, and the reason why using fixed cells for measuring cellular dimensions can result in serious underestimation ofin vivovalues. We further consider the evidence that individual buds and hyphae grow linearly and that exponential growth of the population results from regular formation of new daughter cells and regular hyphal branching. Our calculations show that hyphal growth allowsC. albicansto cover much larger distances per unit of time than the yeast mode of growth and that this is accompanied by strongly increased surface expansion rates. We therefore predict that the transcript levels of genes involved in wall formation increase during hyphal growth. Interestingly, wall proteins and polysaccharides seem barely, if at all, subject to turnover and replacement. A general lesson is how strongly most bionumbers and bioestimates depend on environmental conditions and genetic background, thus reemphasizing the importance of well-defined and carefully chosen culture conditions and experimental approaches. Finally, we propose that the numbers and estimates described here offer a solid starting point for similar studies of other cell compartments and other yeast species.

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Melanin Externalization in Candida albicans Depends on Cell Wall Chitin Structures

Eukaryotic Cell ◽

10.1128/ec.00051-10 ◽

2010 ◽

Vol 9 (9) ◽

pp. 1329-1342 ◽

Cited By ~ 55

Author(s):

Claire A. Walker ◽

Beatriz L. Gómez ◽

Héctor M. Mora-Montes ◽

Kevin S. Mackenzie ◽

Carol A. Munro ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Fungal Pathogen ◽

Cell Walls ◽

Chitin Synthesis ◽

Melanin Production ◽

Content Type ◽

Encoding Gene ◽

Chitinase Genes

ABSTRACT The fungal pathogen Candida albicans produces dark-pigmented melanin after 3 to 4 days of incubation in medium containing l-3,4-dihydroxyphenylalanine (l-DOPA) as a substrate. Expression profiling of C. albicans revealed very few genes significantly up- or downregulated by growth in l-DOPA. We were unable to determine a possible role for melanin in the virulence of C. albicans. However, we showed that melanin was externalized from the fungal cells in the form of electron-dense melanosomes that were free or often loosely bound to the cell wall exterior. Melanin production was boosted by the addition of N-acetylglucosamine to the medium, indicating a possible association between melanin production and chitin synthesis. Melanin externalization was blocked in a mutant specifically disrupted in the chitin synthase-encoding gene CHS2. Melanosomes remained within the outermost cell wall layers in chs3Δ and chs2Δ chs3Δ mutants but were fully externalized in chs8Δ and chs2Δ chs8Δ mutants. All the CHS mutants synthesized dark pigment at equivalent rates from mixed membrane fractions in vitro, suggesting it was the form of chitin structure produced by the enzymes, not the enzymes themselves, that was involved in the melanin externalization process. Mutants with single and double disruptions of the chitinase genes CHT2 and CHT3 and the chitin pathway regulator ECM33 also showed impaired melanin externalization. We hypothesize that the chitin product of Chs3 forms a scaffold essential for normal externalization of melanosomes, while the Chs8 chitin product, probably produced in cell walls in greater quantity in the absence of CHS2, impedes externalization.

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Cell-Biological Studies of Osmotic Shock Response in Streptomyces spp

Journal of Bacteriology ◽

10.1128/jb.00465-16 ◽

2016 ◽

Vol 199 (1) ◽

Cited By ~ 11

Author(s):

Katsuya Fuchino ◽

Klas Flärdh ◽

Paul Dyson ◽

Nora Ausmees

Keyword(s):

Cell Wall ◽

Cell Polarity ◽

Tip Growth ◽

Biological Study ◽

Polar Growth ◽

Hyphal Branching ◽

Content Type ◽

Biological Studies ◽

Wide Range ◽

Tip Extension

ABSTRACT Most bacteria are likely to face osmotic challenges, but there is yet much to learn about how such environmental changes affect the architecture of bacterial cells. Here, we report a cell-biological study in model organisms of the genus Streptomyces, which are actinobacteria that grow in a highly polarized fashion to form branching hyphae. The characteristic apical growth of Streptomyces hyphae is orchestrated by protein assemblies, called polarisomes, which contain coiled-coil proteins DivIVA and Scy, and recruit cell wall synthesis complexes and the stress-bearing cytoskeleton of FilP to the tip regions of the hyphae. We monitored cell growth and cell-architectural changes by time-lapse microscopy in osmotic upshift experiments. Hyperosmotic shock caused arrest of growth, loss of turgor, and hypercondensation of chromosomes. The recovery period was protracted, presumably due to the dehydrated state of the cytoplasm, before hyphae could restore their turgor and start to grow again. In most hyphae, this regrowth did not take place at the original hyphal tips. Instead, cell polarity was reprogrammed, and polarisomes were redistributed to new sites, leading to the emergence of multiple lateral branches from which growth occurred. Factors known to regulate the branching pattern of Streptomyces hyphae, such as the serine/threonine kinase AfsK and Scy, were not involved in reprogramming of cell polarity, indicating that different mechanisms may act under different environmental conditions to control hyphal branching. Our observations of hyphal morphology during the stress response indicate that turgor and sufficient hydration of cytoplasm are required for Streptomyces tip growth. IMPORTANCE Polar growth is an intricate manner of growth for accomplishing a complicated morphology, employed by a wide range of organisms across the kingdoms of life. The tip extension of Streptomyces hyphae is one of the most pronounced examples of polar growth among bacteria. The expansion of the cell wall by tip extension is thought to be facilitated by the turgor pressure, but it was unknown how external osmotic change influences Streptomyces tip growth. We report here that severe hyperosmotic stress causes cessation of growth, followed by reprogramming of cell polarity and rearrangement of growth zones to promote lateral hyphal branching. This phenomenon may represent a strategy of hyphal organisms to avoid osmotic stress encountered by the growing hyphal tip.

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Role of BGS13 in the Secretory Mechanism of Pichia pastoris

Applied and Environmental Microbiology ◽

10.1128/aem.01615-19 ◽

2019 ◽

Vol 85 (24) ◽

Author(s):

Christopher A. Naranjo ◽

Anita D. Jivan ◽

Maria N. Vo ◽

Katherine H. de Sa Campos ◽

Jared S. Deyarmin ◽

...

Keyword(s):

Cell Wall ◽

Protein Kinase C ◽

Protein Kinase ◽

Pichia Pastoris ◽

Mutant Strain ◽

Recombinant Proteins ◽

Economic Benefits ◽

Heterologous Protein Expression ◽

Content Type ◽

Kinase C

ABSTRACT The methylotrophic yeast Pichia pastoris has been utilized for heterologous protein expression for over 30 years. Because P. pastoris secretes few of its own proteins, the exported recombinant protein is the major polypeptide in the extracellular medium, making purification relatively easy. Unfortunately, some recombinant proteins intended for secretion are retained within the cell. A mutant strain isolated in our laboratory, containing a disruption of the BGS13 gene, displayed elevated levels of secretion for a variety of reporter proteins. The Bgs13 peptide (Bgs13p) is similar to the Saccharomyces cerevisiae protein kinase C 1 protein (Pkc1p), but its specific mode of action is currently unclear. To illuminate differences in the secretion mechanism between the wild-type (wt) strain and the bgs13 strain, we determined that the disrupted bgs13 gene expressed a truncated protein that had reduced protein kinase C activity and a different location in the cell, compared to the wt protein. Because the Pkc1p of baker’s yeast plays a significant role in cell wall integrity, we investigated the sensitivity of the mutant strain’s cell wall to growth antagonists and extraction by dithiothreitol, determining that the bgs13 strain cell wall suffered from inherent structural problems although its porosity was normal. A proteomic investigation of the bgs13 strain secretome and cell wall-extracted peptides demonstrated that, compared to its wt parent, the bgs13 strain also displayed increased release of an array of normally secreted, endogenous proteins, as well as endoplasmic reticulum-resident chaperone proteins, suggesting that Bgs13p helps regulate the unfolded protein response and protein sorting on a global scale. IMPORTANCE The yeast Pichia pastoris is used as a host system for the expression of recombinant proteins. Many of these products, including antibodies, vaccine antigens, and therapeutic proteins such as insulin, are currently on the market or in late stages of development. However, one major weakness is that sometimes these proteins are not secreted from the yeast cell efficiently, which impedes and raises the cost of purification of these vital proteins. Our laboratory has isolated a mutant strain of Pichia pastoris that shows enhanced secretion of many proteins. The mutant produces a modified version of Bgs13p. Our goal is to understand how the change in the Bgs13p function leads to improved secretion. Once the Bgs13p mechanism is illuminated, we should be able to apply this understanding to engineer new P. pastoris strains that efficiently produce and secrete life-saving recombinant proteins, providing medical and economic benefits.

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Metabolic Reprogramming in the Opportunistic Yeast Candida albicans in Response to Hypoxia

mSphere ◽

10.1128/msphere.00913-19 ◽

2020 ◽

Vol 5 (1) ◽

Cited By ~ 2

Author(s):

Anaïs Burgain ◽

Faiza Tebbji ◽

Inès Khemiri ◽

Adnane Sellam

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Metabolic Pathways ◽

Membrane Lipids ◽

Oxygen Depletion ◽

Metabolic Reprogramming ◽

Pathogenic Yeast ◽

Fungal Virulence ◽

Content Type ◽

The Impact

ABSTRACT Hypoxia is the predominant condition that the human opportunistic fungus Candida albicans encounters in the majority of the colonized niches within the host. So far, the impact of such a condition on the overall metabolism of this important human-pathogenic yeast has not been investigated. Here, we have undertaken a time-resolved metabolomics analysis to uncover the metabolic landscape of fungal cells experiencing hypoxia. Our data showed a dynamic reprogramming of many fundamental metabolic pathways, such as glycolysis, the pentose phosphate pathway, and different metabolic routes related to fungal cell wall biogenesis. The C. albicans lipidome was highly affected by oxygen depletion, with an increased level of free fatty acids and biochemical intermediates of membrane lipids, including phospholipids, lysophospholipids, sphingolipids, and mevalonate. The depletion of oxygen-dependent lipids such as ergosterol or phosphatidylcholine with longer and polyunsaturated lateral fatty acid chains was observed only at the later hypoxic time point (180 min). Transcriptomics data supported the main metabolic response to hypoxia when matched to our metabolomic profiles. The hypoxic metabolome reflected different physiological alterations of the cell wall and plasma membrane of C. albicans under an oxygen-limiting environment that were confirmed by different approaches. This study provided a framework for future in vivo investigations to examine relevant hypoxic metabolic trajectories in fungal virulence and fitness within the host. IMPORTANCE A critical aspect of cell fitness is the ability to sense and adapt to variations in oxygen levels in their local environment. Candida albicans is an opportunistic yeast that is the most prevalent human fungal pathogen. While hypoxia is the predominant condition that C. albicans encounters in most of its niches, its impact on fungal metabolism remains unexplored so far. Here, we provided a detailed landscape of the C. albicans metabolome that emphasized the importance of many metabolic routes for the adaptation of this yeast to oxygen depletion. The fungal hypoxic metabolome identified in this work provides a framework for future investigations to assess the contribution of relevant metabolic pathways in the fitness of C. albicans and other human eukaryotic pathogens with similar colonized human niches. As hypoxia is present at most of the fungal infection foci in the host, hypoxic metabolic pathways are thus an attractive target for antifungal therapy.

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Remasking of Candida albicans β-Glucan in Response to Environmental pH Is Regulated by Quorum Sensing

mBio ◽

10.1128/mbio.02347-19 ◽

2019 ◽

Vol 10 (5) ◽

Cited By ~ 7

Author(s):

Fabien Cottier ◽

Sarah Sherrington ◽

Sarah Cockerill ◽

Valentina del Olmo Toledo ◽

Stephen Kissane ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Quorum Sensing ◽

Immune Responses ◽

Female Reproductive Tract ◽

Innate Immune ◽

Immune Recognition ◽

Innate Immune Responses ◽

Content Type ◽

Cell Wall Remodeling

ABSTRACT Candida albicans is a commensal yeast of the human gut which is tolerated by the immune system but has the potential to become an opportunistic pathogen. One way in which C. albicans achieves this duality is through concealing or exposing cell wall pathogen-associated molecular patterns (PAMPs) in response to host-derived environment cues (pH, hypoxia, and lactate). This cell wall remodeling allows C. albicans to evade or hyperactivate the host’s innate immune responses, leading to disease. Previously, we showed that adaptation of C. albicans to acidic environments, conditions encountered during colonization of the female reproductive tract, induces significant cell wall remodeling resulting in the exposure of two key fungal PAMPs (β-glucan and chitin). Here, we report that this pH-dependent cell wall remodeling is time dependent, with the initial change in pH driving cell wall unmasking, which is then remasked at later time points. Remasking of β-glucan was mediated via the cell density-dependent fungal quorum sensing molecule farnesol, while chitin remasking was mediated via a small, heat-stable, nonproteinaceous secreted molecule(s). Transcript profiling identified a core set of 42 genes significantly regulated by pH over time and identified the transcription factor Efg1 as a regulator of chitin exposure through regulation of CHT2. This dynamic cell wall remodeling influenced innate immune recognition of C. albicans, suggesting that during infection, C. albicans can manipulate the host innate immune responses. IMPORTANCE Candida albicans is part of the microbiota of the skin and gastrointestinal and reproductive tracts of humans and has coevolved with us for millennia. During that period, C. albicans has developed strategies to modulate the host’s innate immune responses, by regulating the exposure of key epitopes on the fungal cell surface. Here, we report that exposing C. albicans to an acidic environment, similar to the one of the stomach or vagina, increases the detection of the yeast by macrophages. However, this effect is transitory, as C. albicans is able to remask these epitopes (glucan and chitin). We found that glucan remasking is controlled by the production of farnesol, a molecule secreted by C. albicans in response to high cell densities. However, chitin-remasking mechanisms remain to be identified. By understanding the relationship between environmental sensing and modulation of the host-pathogen interaction, new opportunities for the development of innovative antifungal strategies are possible.

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Curcumin Targets Cell Wall Integrity via Calcineurin-Mediated Signaling in Candida albicans

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01385-13 ◽

2013 ◽

Vol 58 (1) ◽

pp. 167-175 ◽

Cited By ~ 48

Author(s):

Awanish Kumar ◽

Sanjiveeni Dhamgaye ◽

Indresh Kumar Maurya ◽

Ashutosh Singh ◽

Monika Sharma ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Critical Role ◽

Pathogenic Fungi ◽

Cell Wall Integrity ◽

Ergosterol Biosynthesis ◽

Ros Generation ◽

Calcofluor White ◽

Content Type ◽

Cell Wall Damage

ABSTRACTCurcumin (CUR) shows antifungal activity against a range of pathogenic fungi, includingCandida albicans. The reported mechanisms of action of CUR include reactive oxygen species (ROS) generation, defects in the ergosterol biosynthesis pathway, decrease in hyphal development, and modulation of multidrug efflux pumps. Reportedly, each of these pathways is independently linked to the cell wall machinery inC. albicans, but surprisingly, CUR has not been previously implicated in cell wall damage. In the present study, we performed transcriptional profiling to identify the yet-unidentified targets of CUR inC. albicans. We found that, among 348 CUR-affected genes, 51 were upregulated and 297 were downregulated. Interestingly, most of the cell wall integrity pathway genes were downregulated. The possibility of the cell wall playing a critical role in the mechanism of CUR required further validation; therefore, we performed specific experiments to establish if there was any link between the two. The fractional inhibitory concentration index values of 0.24 to 0.37 show that CUR interacts synergistically with cell wall-perturbing (CWP) agents (caspofungin, calcofluor white, Congo red, and SDS). Furthermore, we could observe cell wall damage and membrane permeabilization by CUR alone, as well as synergistically with CWP agents. We also found hypersusceptibility in calcineurin and mitogen-activated protein (MAP) kinase pathway mutants against CUR, which confirmed that CUR also targets cell wall biosynthesis inC. albicans. Together, these data provide strong evidence that CUR disrupts cell wall integrity inC. albicans. This new information on the mechanistic action of CUR could be employed in improving treatment strategies and in combinatorial drug therapy.

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Multiple Alternative Carbon Pathways Combine To Promote Candida albicans Stress Resistance, Immune Interactions, and Virulence

mBio ◽

10.1128/mbio.03070-19 ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 10

Author(s):

Robert B. Williams ◽

Michael C. Lorenz

Keyword(s):

Amino Acids ◽

Cell Wall ◽

Candida Albicans ◽

Stress Resistance ◽

Innate Immune System ◽

Carbon Sources ◽

Innate Immune ◽

Content Type ◽

Multiple Alternative ◽

Carbon Pathways

ABSTRACT The phagocytic cells of the innate immune system are an essential first line of antimicrobial defense, and yet Candida albicans, one of the most problematic fungal pathogens, is capable of resisting the stresses imposed by the macrophage phagosome, eventually resulting in the destruction of the phagocyte. C. albicans rapidly adapts to the phagosome by upregulating multiple alternative carbon utilization pathways, particularly those for amino acids, carboxylic acids, and N-acetylglucosamine (GlcNAc). Here, we report that C. albicans recognizes these carbon sources both as crucial nutrients and as independent signals in its environment. Even in the presence of glucose, each carbon source promotes increased resistance to a unique profile of stressors; lactate promotes increased resistance to osmotic and cell wall stresses, amino acids increased resistance to oxidative and nitrosative stresses, and GlcNAc increased resistance to oxidative stress and caspofungin, while all three alternative carbon sources have been shown to induce resistance to fluconazole. Moreover, we show mutants incapable of utilizing these carbon sources, in particular, strains engineered to be defective in all three pathways, are significantly attenuated in both macrophage and mouse models, with additive effects observed as multiple carbon pathways are eliminated, suggesting that C. albicans simultaneously utilizes multiple carbon sources within the macrophage phagosome and during disseminated candidiasis. Taking the data together, we propose that, in addition to providing energy to the pathogen within host environments, alternative carbon sources serve as niche-specific priming signals that allow C. albicans to recognize microenvironments within the host and to prepare for stresses associated with that niche, thus promoting host adaptation and virulence. IMPORTANCE Candida albicans is a fungal pathogen and a significant cause of morbidity and mortality, particularly in people with defects, sometimes minor ones, in innate immunity. The phagocytes of the innate immune system, particularly macrophages and neutrophils, generally restrict this organism to its normal commensal niches, but C. albicans shows a robust and multifaceted response to these cell types. Inside macrophages, a key component of this response is the activation of multiple pathways for the utilization of alternative carbon sources, particularly amino acids, carboxylic acids, and N-acetylglucosamine. These carbon sources are key sources of energy and biomass but also independently promote stress resistance, induce cell wall alterations, and affect C. albicans interactions with macrophages. Engineered strains incapable of utilizing these alternative carbon pathways are attenuated in infection models. These data suggest that C. albicans recognizes nutrient composition as an indicator of specific host environments and tailors its responses accordingly.

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