scholarly journals Control of Candida albicans Metabolism and Biofilm Formation by Pseudomonas aeruginosa Phenazines

mBio ◽  
2013 ◽  
Vol 4 (1) ◽  
Author(s):  
Diana K. Morales ◽  
Nora Grahl ◽  
Chinweike Okegbe ◽  
Lars E. P. Dietrich ◽  
Nicholas J. Jacobs ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Candida Albicans ◽  
Biofilm Formation ◽  
Carbon Sources ◽  
Metabolic Effects ◽  
Respiratory Metabolism ◽  
Fermentation Products ◽  
Content Type ◽  
Opportunistic Fungal Pathogen ◽  
Biofilm Development

ABSTRACTCandida albicanshas developmental programs that govern transitions between yeast and filamentous morphologies and between unattached and biofilm lifestyles. Here, we report that filamentation, intercellular adherence, and biofilm development were inhibited during interactions betweenCandida albicansandPseudomonas aeruginosathrough the action ofP. aeruginosa-produced phenazines. While phenazines are toxic toC. albicansat millimolar concentrations, we found that lower concentrations of any of three different phenazines (pyocyanin, phenazine methosulfate, and phenazine-1-carboxylate) allowed growth but affected the development ofC. albicanswrinkled colony biofilms and inhibited the fungal yeast-to-filament transition. Phenazines impairedC. albicansgrowth on nonfermentable carbon sources and led to increased production of fermentation products (ethanol, glycerol, and acetate) in glucose-containing medium, leading us to propose that phenazines specifically inhibited respiration. Methylene blue, another inhibitor of respiration, also prevented the formation of structured colony biofilms. The inhibition of filamentation and colony wrinkling was not solely due to lowered extracellular pH induced by fermentation. Compared to smooth, unstructured colonies, wrinkled colony biofilms had higher oxygen concentrations within the colony, and wrinkled regions of these colonies had higher levels of respiration. Together, our data suggest that the structure of the fungal biofilm promotes access to oxygen and enhances respiratory metabolism and that the perturbation of respiration by bacterial molecules such as phenazines or compounds with similar activities disrupts these pathways. These findings may suggest new ways to limit fungal biofilms in the context of disease.IMPORTANCEMany of the infections caused byCandida albicans, a major human opportunistic fungal pathogen, involve both morphological transitions and the formation of surface-associated biofilms. Through the study ofC. albicansinteractions with the bacteriumPseudomonas aeruginosa, which often coinfects withC. albicans, we have found thatP. aeruginosa-produced phenazines modulateC. albicansmetabolism and, through these metabolic effects, impact cellular morphology, cell-cell interactions, and biofilm formation. We suggest that the structure ofC. albicansbiofilms promotes access to oxygen and enhances respiratory metabolism and that the perturbation of respiration by phenazines inhibits biofilm development. Our findings not only provide insight into interactions between these species but also provide valuable insights into novel pathways that could lead to the development of new therapies to treatC. albicansinfections.

scholarly journals Sodium Lactate Negatively Regulates Shewanella putrefaciens CN32 Biofilm Formation via a Three-Component Regulatory System (LrbS-LrbA-LrbR)

2017 ◽  
Vol 83 (14) ◽  
Author(s):  
Cong Liu ◽  
Jinshui Yang ◽  
Liang Liu ◽  
Baozhen Li ◽  
Hongli Yuan ◽  
...  
Keyword(s):  
Carbon Source ◽  
Biofilm Formation ◽  
Present Report ◽  
Carbon Sources ◽  
Regulatory System ◽  
Shewanella Putrefaciens ◽  
Sodium Lactate ◽  
Signal Molecule ◽  
Content Type ◽  
Biofilm Development

ABSTRACT The capability of biofilm formation has a major impact on the industrial and biotechnological applications of Shewanella putrefaciens CN32. However, the detailed regulatory mechanisms underlying biofilm formation in this strain remain largely unknown. In the present report, we describe a three-component regulatory system which negatively regulates the biofilm formation of S. putrefaciens CN32. This system consists of a histidine kinase LrbS (Sputcn32_0303) and two cognate response regulators, including a transcription factor, LrbA (Sputcn32_0304), and a phosphodiesterase, LrbR (Sputcn32_0305). LrbS responds to the signal of the carbon source sodium lactate and subsequently activates LrbA. The activated LrbA then promotes the expression of lrbR, the gene for the other response regulator. The bis-(3′-5′)-cyclic dimeric GMP (c-di-GMP) phosphodiesterase LrbR, containing an EAL domain, decreases the concentration of intracellular c-di-GMP, thereby negatively regulating biofilm formation. In summary, the carbon source sodium lactate acts as a signal molecule that regulates biofilm formation via a three-component regulatory system (LrbS-LrbA-LrbR) in S. putrefaciens CN32. IMPORTANCE Biofilm formation is a significant capability used by some bacteria to survive in adverse environments. Numerous environmental factors can affect biofilm formation through different signal transduction pathways. Carbon sources are critical nutrients for bacterial growth, and their concentrations and types significantly influence the biomass and structure of biofilms. However, knowledge about the underlying mechanism of biofilm formation regulation by carbon source is still limited. This work elucidates a modulation pattern of biofilm formation negatively regulated by sodium lactate as a carbon source via a three-component regulatory system in S. putrefaciens CN32, which may serve as a good example for studying how the carbon sources impact biofilm development in other bacteria.

scholarly journals Pseudomonas aeruginosa secreted factors impair biofilm development in Candida albicans

Microbiology ◽  
2010 ◽  
Vol 156 (5) ◽  
pp. 1476-1486 ◽  
Author(s):  
Lucy J. Holcombe ◽  
Gordon McAlester ◽  
Carol A. Munro ◽  
Brice Enjalbert ◽  
Alistair J. P. Brown ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Candida Albicans ◽  
Biofilm Formation ◽  
Bacterial Species ◽  
Homoserine Lactone ◽  
Strong Increase ◽  
Opportunistic Pathogens ◽  
Secreted Factors ◽  
Expression Of Genes ◽  
Biofilm Development

Signal-mediated interactions between the human opportunistic pathogens Pseudomonas aeruginosa and Candida albicans affect virulence traits in both organisms. Phenotypic studies revealed that bacterial supernatant from four P. aeruginosa strains strongly reduced the ability of C. albicans to form biofilms on silicone. This was largely a consequence of inhibition of biofilm maturation, a phenomenon also observed with supernatant prepared from non-clinical bacterial species. The effects of supernatant on biofilm formation were not mediated via interference with the yeast–hyphal morphological switch and occurred regardless of the level of homoserine lactone (HSL) produced, indicating that the effect is HSL-independent. A transcriptome analysis to dissect the effects of the P. aeruginosa supernatants on gene expression in the early stages of C. albicans biofilm formation identified 238 genes that exhibited reproducible changes in expression in response to all four supernatants. In particular, there was a strong increase in the expression of genes related to drug or toxin efflux and a decrease in expression of genes associated with adhesion and biofilm formation. Furthermore, expression of YWP1, which encodes a protein known to inhibit biofilm formation, was significantly increased. Biofilm formation is a key aspect of C. albicans infections, therefore the capacity of P. aeruginosa to antagonize this has clear biomedical implications.

Candida tropicalis RON1 is required for hyphal formation, biofilm development, and virulence but is dispensable for N-acetylglucosamine catabolism

2020 ◽  
Author(s):  
Yu-De Song ◽  
Chih-Chieh Hsu ◽  
Shi Qian Lew ◽  
Ching-Hsuan Lin
Keyword(s):  
Candida Albicans ◽  
Candida Tropicalis ◽  
Biofilm Formation ◽  
Carbon Sources ◽  
Protein Alignment ◽  
Gene Expressions ◽  
Glucose Content ◽  
Catabolic Genes ◽  
Hyphal Formation ◽  
Biofilm Development

Abstract NDT80-like family genes are highly conserved across a large group of fungi, but the functions of each Ndt80 protein are diverse and have evolved differently among yeasts and pathogens. The unique NDT80 gene in budding yeast is required for sexual reproduction, whereas three NDT80-like genes, namely, NDT80, REP1, and RON1, found in Candida albicans exhibit distinct functions. Notably, it was suggested that REP1, rather than RON1, is required for N-acetylglucosamine (GlcNAc) catabolism. Although Candida tropicalis, a widely dispersed fungal pathogen in tropical and subtropical areas, is closely related to Candida albicans, its phenotypic, pathogenic and environmental adaptation characteristics are remarkably divergent. In this study, we focused on the Ron1 transcription factor in C. tropicalis. Protein alignment showed that C. tropicalis Ron1 (CtRon1) shares 39.7% identity with C. albicans Ron1 (CaRon1). Compared to the wild-type strain, the C. tropicalis ron1Δ strains exhibited normal growth in different carbon sources and had similar expression levels of several GlcNAc catabolic genes during GlcNAc treatment. In contrast, C. tropicalis REP1 is responsible for GlcNAc catabolism and is involved in GlcNAc catabolic gene expressions, similar to C. albicans Rep1. However, REP1 deletion strains in C. tropicalis promote hyphal development in GlcNAc with low glucose content. Interestingly, CtRON1, but not CaRON1, deletion mutants exhibited significantly impaired hyphal growth and biofilm formation. As expected, CtRON1 was required for full virulence. Together, the results of this study showed divergent functions of CtRon1 compared to CaRon1; CtRon1 plays a key role in yeast-hyphal dimorphism, biofilm formation and virulence. Lay Abstract In this study, we identified the role of RON1, an NDT80-like gene, in Candida tropicalis. Unlike the gene in Candida albicans, our studies showed that RON1 is a key regulator of hyphal formation, biofilm development and virulence but is dispensable for N-acetylglucosamine catabolism in C. tropicalis.

scholarly journals O-Mannosylation in Candida albicans Enables Development of Interkingdom Biofilm Communities

mBio ◽  
2014 ◽  
Vol 5 (2) ◽  
Author(s):  
Lindsay C. Dutton ◽  
Angela H. Nobbs ◽  
Katy Jepson ◽  
Mark A. Jepson ◽  
M. Margaret Vickerman ◽  
...  
Keyword(s):  
Cell Wall ◽  
Candida Albicans ◽  
Biofilm Formation ◽  
Early Stage ◽  
Growth Conditions ◽  
Wild Type ◽  
Content Type ◽  
Subsequent Performance ◽  
Biofilm Development ◽  
Mutant Cells

ABSTRACTCandida albicansis a fungus that colonizes oral cavity surfaces, the gut, and the genital tract.Streptococcus gordoniiis a ubiquitous oral bacterium that has been shown to form biofilm communities withC. albicans. Formation of dual-speciesS. gordonii-C. albicansbiofilm communities involves interaction of theS. gordoniiSspB protein with the Als3 protein on the hyphal filament surface ofC. albicans. Mannoproteins comprise a major component of theC. albicanscell wall, and in this study we sought to determine if mannosylation in cell wall biogenesis ofC. albicanswas necessary for hyphal adhesin functions associated with interkingdom biofilm development. AC. albicans mnt1Δmnt2Δ mutant, with deleted α-1,2-mannosyltransferase genes and thus defective inO-mannosylation, was abrogated in biofilm formation under various growth conditions and produced hyphal filaments that were not recognized byS. gordonii. Cell wall proteomes of hypha-formingmnt1Δmnt2Δ mutant cells showed growth medium-dependent alterations, compared to findings for the wild type, in a range of protein components, including Als1, Als3, Rbt1, Scw1, and Sap9. Hyphal filaments formed bymnt1Δmnt2Δ mutant cells, unlike wild-type hyphae, did not interact withC. albicansAls3 or Hwp1 partner cell wall proteins or withS. gordoniiSspB partner adhesin, suggesting defective functionality of adhesins on themnt1Δmnt2Δ mutant. These observations imply that early stageO-mannosylation is critical for activation of hyphal adhesin functions required for biofilm formation, recognition by bacteria such asS. gordonii, and microbial community development.IMPORTANCEIn the human mouth, microorganisms form communities known as biofilms that adhere to the surfaces present.Candida albicansis a fungus that is often found within these biofilms. We have focused on the mechanisms by whichC. albicansbecomes incorporated into communities containing bacteria, such asStreptococcus. We find that impairment of early stage addition of mannose sugars toC. albicanshyphal filament proteins deleteriously affects their subsequent performance in mediating formation of polymicrobial biofilms. Our analyses provide new understanding of the way that microbial communities develop, and of potential means to controlC. albicansinfections.

scholarly journals N -Acetylglucosamine (GlcNAc)-Inducible Gene GIG2 Is a Novel Component of GlcNAc Metabolism in Candida albicans

2013 ◽  
Vol 13 (1) ◽  
pp. 66-76 ◽  
Author(s):  
Swagata Ghosh ◽  
Kongara Hanumantha Rao ◽  
Neel Sarovar Bhavesh ◽  
Gobardhan Das ◽  
Ved Prakash Dwivedi ◽  
...  
Keyword(s):  
Candida Albicans ◽  
Carbon Sources ◽  
Transcriptional Responses ◽  
Content Type ◽  
Metabolic Intermediates ◽  
Catabolic Genes ◽  
Opportunistic Fungal Pathogen ◽  
Targeted Inhibition ◽  
Mutant Cells ◽  
Insight Into

ABSTRACT Candida albicans is an opportunistic fungal pathogen that resides in the human body as a commensal and can turn pathogenic when the host is immunocompromised. Adaptation of C. albicans to host niche-specific conditions is important for the establishment of pathogenicity, where the ability of C. albicans to utilize multiple carbon sources provides additional flexibility. One alternative sugar is N -acetylglucosamine (GlcNAc), which is now established as an important carbon source for many pathogens and can also act as a signaling molecule. Although GlcNAc catabolism has been well studied in many pathogens, the importance of several enzymes involved in the formation of metabolic intermediates still remains elusive. In this context, microarray analysis was carried out to investigate the transcriptional responses induced by GlcNAc under different conditions. A novel gene that was highly upregulated immediately following the GlcNAc catabolic genes was identified and was named GIG2 (GlcNAc-induced gene 2). This gene is regulated in a manner distinct from that of the GlcNAc-induced genes described previously in that GlcNAc metabolism is essential for its induction. Furthermore, this gene is involved in the metabolism of N -acetylneuraminate (sialic acid), a molecule equally important for initial host-pathogen recognition. Mutant cells showed a considerable decrease in fungal burden in mouse kidneys and were hypersensitive to oxidative stress conditions. Since GIG2 is also present in many other fungal and enterobacterial genomes, targeted inhibition of its activity would offer insight into the treatment of candidiasis and other fungal or enterobacterial infections.

scholarly journals Improved Gene Ontology Annotation for Biofilm Formation, Filamentous Growth, and Phenotypic Switching in Candida albicans

2012 ◽  
Vol 12 (1) ◽  
pp. 101-108 ◽  
Author(s):  
Diane O. Inglis ◽  
Marek S. Skrzypek ◽  
Martha B. Arnaud ◽  
Jonathan Binkley ◽  
Prachi Shah ◽  
...  
Keyword(s):  
Gene Ontology ◽  
Candida Albicans ◽  
Gene Product ◽  
Fungal Pathogen ◽  
Biofilm Formation ◽  
Filamentous Growth ◽  
Phenotypic Switching ◽  
Gene Products ◽  
Content Type ◽  
Opportunistic Fungal Pathogen

ABSTRACTThe opportunistic fungal pathogenCandida albicansis a significant medical threat, especially for immunocompromised patients. Experimental research has focused on specific areas ofC. albicansbiology, with the goal of understanding the multiple factors that contribute to its pathogenic potential. Some of these factors include cell adhesion, invasive or filamentous growth, and the formation of drug-resistant biofilms. The Gene Ontology (GO) (www.geneontology.org) is a standardized vocabulary that theCandidaGenome Database (CGD) (www.candidagenome.org) and other groups use to describe the functions of gene products. To improve the breadth and accuracy of pathogenicity-related gene product descriptions and to facilitate the description of as yet uncharacterized but potentially pathogenicity-related genes inCandidaspecies, CGD undertook a three-part project: first, the addition of terms to the biological process branch of the GO to improve the description of fungus-related processes; second, manual recuration of gene product annotations in CGD to use the improved GO vocabulary; and third, computational ortholog-based transfer of GO annotations from experimentally characterized gene products, using these new terms, to uncharacterized orthologs in otherCandidaspecies. Through genome annotation and analysis, we identified candidate pathogenicity genes in seven non-C. albicans Candidaspecies and in one additionalC. albicansstrain, WO-1. We also defined a set ofC. albicansgenes at the intersection of biofilm formation, filamentous growth, pathogenesis, and phenotypic switching of this opportunistic fungal pathogen, which provides a compelling list of candidates for further experimentation.

scholarly journals Role of quorum sensing in UVA-induced biofilm formation in Pseudomonas aeruginosa

Microbiology ◽  
2020 ◽  
Vol 166 (8) ◽  
pp. 735-750 ◽  
Author(s):  
Magdalena Pezzoni ◽  
Ramón A. Pizarro ◽  
Cristina S. Costa
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Quorum Sensing ◽  
Biofilm Formation ◽  
Type Species ◽  
Transcriptional Level ◽  
Content Type ◽  
Link Type ◽  
Opportunistic Human Pathogen ◽  
Biofilm Development

Pseudomonas aeruginosa , a versatile bacterium present in terrestrial and aquatic environments and a relevant opportunistic human pathogen, is largely known for the production of robust biofilms. The unique properties of these structures complicate biofilm eradication, because they make the biofilms very resistant to diverse antibacterial agents. Biofilm development and establishment is a complex process regulated by multiple regulatory genetic systems, among them is quorum sensing (QS), a mechanism employed by bacteria to regulate gene transcription in response to population density. In addition, environmental factors such as UVA radiation (400–315 nm) have been linked to biofilm formation. In this work, we further investigate the mechanism underlying the induction of biofilm formation by UVA, analysing the role of QS in this phenomenon. We demonstrate that UVA induces key genes of the Las and Rhl QS systems at the transcriptional level. We also report that pelA and pslA genes, which are essential for biofilm formation and whose transcription depends in part on QS, are significantly induced under UVA exposure. Finally, the results demonstrate that in a relA strain (impaired for ppGpp production), the UVA treatment does not induce biofilm formation or QS genes, suggesting that the increase of biofilm formation due to exposure to UVA in P. aeruginosa could rely on a ppGpp-dependent QS induction.

scholarly journals Candida albicansDispersed Cells Are Developmentally Distinct from Biofilm and Planktonic Cells

mBio ◽  
2018 ◽  
Vol 9 (4) ◽  
Author(s):  
Priya Uppuluri ◽  
Maikel Acosta Zaldívar ◽  
Matthew Z. Anderson ◽  
Matthew J. Dunn ◽  
Judith Berman ◽  
...  
Keyword(s):  
Gene Expression ◽  
Candida Albicans ◽  
Carbon Sources ◽  
Yeast Cells ◽  
Direct Access ◽  
Molecular Characteristics ◽  
Content Type ◽  
Biofilm Dispersal ◽  
Biofilm Development ◽  
Dispersed Cells

ABSTRACTCandida albicanssurface-attached biofilms such as those formed on intravenous catheters with direct access to the bloodstream often serve as a nidus for continuous release of cells capable of initiating new infectious foci. We previously reported that cells dispersed from a biofilm are yeast cells that originate from the top-most hyphal layers of the biofilm. Compared to their planktonic counterparts, these biofilm dispersal yeast cells displayed enhanced virulence-associated characteristics and drug resistance. However, little is known about their molecular properties. To address that issue, in this study we aimed to define the molecular characteristics of these biofilm dispersal cells. We found that the inducer of dispersal,PES1, genetically interacts with the repressor of filamentation,NRG1, in a manner consistent with the definition of dispersed cells as yeast cells. Further, using a flow biofilm model, we performed comprehensive comparative RNA sequencing on freshly dispersed cells in order to identify unique transcriptomic characteristics. Gene expression analysis demonstrated that dispersed cells largely inherit a biofilm-like mRNA profile. Strikingly, however, dispersed cells seemed transcriptionally reprogrammed to acquire nutrients such as zinc and amino acids and to metabolize alternative carbon sources, while their biofilm-associated parent cells did not induce the same high-affinity transporters or express gluconeogenetic genes, despite exposure to the same nutritional signals. Collectively, the findings from this study characterize cell dispersal as an intrinsic step of biofilm development which generates propagules more adept at colonizing distant host sites. This developmental step anticipates the need for virulence-associated gene expression before the cells experience the associated external signals.IMPORTANCECandida albicanssurface-attached biofilms serve as a reservoir of cells to perpetuate and expand an infection; cells released from biofilms on catheters have direct access to the bloodstream. Biofilm dispersal yeast cells exhibit enhanced adhesion, invasion, and biofilm formation compared to their planktonic counterparts. Here, we show using transcriptome sequencing (RNA-seq) that dispersed yeast cells are developmentally distinct from the cells in their parent biofilms as well as from planktonic yeast cells. Dispersal cells possess an anticipatory expression pattern that primes them to infect new sites in the host, to survive in nutrient-starved niches, and to invade new sites. These studies identified dispersal cells as a unique proliferative cell type of the biofilm and showed that they could serve as targets for antibiofilm drug development in the future.

scholarly journals Unique, Diverged, and Conserved Mitochondrial Functions InfluencingCandida albicansRespiration

mBio ◽  
2019 ◽  
Vol 10 (3) ◽  
Author(s):  
Nuo Sun ◽  
Rebecca S. Parrish ◽  
Richard A. Calderone ◽  
William A. Fonzi
Keyword(s):  
Candida Albicans ◽  
Fungal Pathogen ◽  
Complex I ◽  
Electron Transport Chain ◽  
Complex Iii ◽  
Respiratory Metabolism ◽  
Content Type ◽  
Transport Chain ◽  
Opportunistic Fungal Pathogen ◽  
Lineage Specific Genes

ABSTRACTCandida albicansis an opportunistic fungal pathogen of major clinical concern. The virulence of this pathogen is intimately intertwined with its metabolism. Mitochondria, which have a central metabolic role, have undergone many lineage-specific adaptations in association with their eukaryotic host. A screen for lineage-specific genes identified seven such genes specific to the CTG clade of fungi, of whichC. albicansis a member. Each is required for respiratory growth and is integral to expression of complex I, III, or IV of the electron transport chain. Two genes,NUO3andNUO4, encode supernumerary subunits of complex I, whereasNUE1andNUE2have nonstructural roles in expression of complex I. Similarly, the other three genes have nonstructural roles in expression of complex III (QCE1) or complex IV (COE1andCOE2). In addition to these novel additions, an alternative functional assignment was found for the mitochondrial protein encoded byMNE1.MNE1was required for complex I expression inC. albicans, whereas the distantly relatedSaccharomyces cerevisiaeortholog participates in expression of complex III. Phenotypic analysis of deletion mutants showed that fermentative metabolism is unable to support optimal growth rates or yields ofC. albicans. However, yeast-hypha morphogenesis, an important virulence attribute, did not require respiratory metabolism under hypoxic conditions. The inability to respire also resulted in hypersensitivity to the antifungal fluconazole and in attenuated virulence in aGalleria mellonellainfection model. The results show that lineage-specific adaptations have occurred inC. albicansmitochondria and highlight the significance of respiratory metabolism in the pathobiology ofC. albicans.IMPORTANCECandida albicansis an opportunistic fungal pathogen of major clinical concern. The virulence of this pathogen is intimately intertwined with its metabolic behavior, and mitochondria have a central role in that metabolism. Mitochondria have undergone many evolutionary changes, which include lineage-specific adaptations in association with their eukaryotic host. Seven lineage-specific genes required for electron transport chain function were identified in the CTG clade of fungi, of whichC. albicansis a member. Additionally, examination of several highly diverged orthologs encoding mitochondrial proteins demonstrated functional reassignment for one of these. Deficits imparted by deletion of these genes revealed the critical role of respiration in virulence attributes of the fungus and highlight important evolutionary adaptations inC. albicansmetabolism.

scholarly journals Loss of the Two-Component System TctD-TctE in Pseudomonas aeruginosa Affects Biofilm Formation and Aminoglycoside Susceptibility in Response to Citric Acid

mSphere ◽  
2019 ◽  
Vol 4 (2) ◽  
Author(s):  
Patrick K. Taylor ◽  
Li Zhang ◽  
Thien-Fah Mah
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Citric Acid ◽  
Carbon Source ◽  
Biofilm Formation ◽  
Two Component System ◽  
Component System ◽  
Content Type ◽  
Metabolic Versatility ◽  
Two Component ◽  
Biofilm Development

ABSTRACT The two-component system TctD-TctE is important for regulating the uptake of tricarboxylic acids in Pseudomonas aeruginosa. TctD-TctE accomplishes this through derepression of the gene opdH, which encodes a tricarboxylic acid-specific porin. Previous work from our lab revealed that TctD-TctE in P. aeruginosa also has a role in resistance to aminoglycoside antibiotics. The aim of this study was to further characterize the role of TctD-TctE in P. aeruginosa in the presence of citric acid. Here it was found that deletion of P. aeruginosa PA14 TctD-TctE (ΔtctED) resulted in a 4-fold decrease in the biofilm bactericidal concentrations of the aminoglycosides tobramycin and gentamicin when citric acid was present in nutrient media. Tobramycin accumulation assays demonstrated that deletion of TctD-TctE resulted in an increase in the amount of tobramycin retained in biofilm cells. The PA14 wild type responded to increasing concentrations of citric acid by producing less biofilm. In contrast, the amount of ΔtctED mutant biofilm formation remained constant or enhanced. Furthermore, the ΔtctED strain was incapable of growing on citric acid as a sole carbon source and was highly reduced in its ability to grow in the presence of citric acid even when an additional carbon source was available. Use of phenotypic and genetic microarrays found that this growth deficiency of the ΔtctED mutant is unique to citric acid and that multiple metabolic genes are dysregulated. This work demonstrates that TctD-TctE in P. aeruginosa has a role in biofilm development that is dependent on citric acid and that is separate from the previously characterized involvement in resistance to antibiotics. IMPORTANCE Nutrient availability is an important contributor to the ability of bacteria to establish successful infections in a host. Pseudomonas aeruginosa is an opportunistic pathogen in humans causing infections that are difficult to treat. In part, its success is attributable to a high degree of metabolic versatility. P. aeruginosa is able to sense and respond to varied and limited nutrient stress in the host environment. Two-component systems are important sensors-regulators of cellular responses to environmental stresses, such as those encountered in the host. This work demonstrates that the response by the two-component system TctD-TctE to the presence of citric acid has a role in biofilm formation, aminoglycoside susceptibility, and growth in P. aeruginosa.

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