Project description:Candida albicans is an opportunistic fungal pathogen that can infect oral mucosal surfaces despite being under continuous flow from saliva. Previous studies have shown that under specific conditions C. albicans will form microcolonies that more closely resemble the biofilms formed in vivo than standard in vitro biofilm models. However, very little is known about these microcolonies, particularly genomic differences between these specialized biofilm structures and the traditional in vitro biofilms. In this study, we used a novel flow system, in which C. albicans spontaneously forms microcolonies, to further characterize the architecture of fungal microcolonies and their genomics compared to non-microcolony conditions. Fungal microcolonies arise from radially branching filamentous hyphae that increasingly intertwine with one another to form extremely dense biofilms, and closely resemble the architecture of in vivo oropharyngeal candidiasis. We identified 20 core microcolony genes that were differentially regulated in flow-induced microcolonies using RNA-seq. These genes included HWP1, ECE1, IHD1, PLB1, HYR1, PGA10, and SAP5. To better understand the regulatory elements for microcolonies, we utilized a predictive algorithm to discover ten transcriptional regulators potentially involved in microcolony formation. Of these transcription factors, we found that six played a key role in microcolony formation and development (Rob1, Ndt80, Efg1, Sfl1, Sfl2, and Nrg1). We also found that Hwp1, Sap5, Pga10, and all the microcolony regulators promoted adhesion and invasion of the microcolonies to oral epithelium. Furthermore, epithelial cells infected with deletion mutants of ROB1, NDT80, SFL2, EFG1, and MCM1 had reduced immune response, evidenced by reduced phosphorylation of MKP1 and c-Fos, key signal transducers in the hyphal invasion response. This profile of microcolony transcriptional regulators more closely reflects Sfl1 and Sfl2 hyphal regulatory networks than biofilm regulatory networks, suggesting that hyphal morphogenesis plays a more central role in the development of flow-induced microcolonies.

Project description:Candida albicans, a major opportunistic fungal pathogen is frequently found together with Streptococcus mutans in dental biofilms associated with severe childhood tooth-decay, a prevalent pediatric oral disease. Previous studies have demonstrated that S. mutans and C. albicans synergizes virulence of plaque-biofilms in vivo. However, the nature of this bacterial-fungal relationship in this cross-kingdom biofilm remains largely uncharacterized. Using iTRAQ based quantitative proteomics, we found that proteins associated with carbohydrate metabolism such as alpha-1,4 glucan phosphorylase, Hexokinase-2, Isocitrate lyase and malate synthase were significantly upregulated in C. albicans in the mixed-species biofilms (P<0.05). C. albicans proteins associated with growth/morphogenesis such as pH-responsive protein-2, Fma1p and Hsp21 were also induced. Conversely, S. mutans proteins in the tricarboxylic acid cycle such as citrate synthase and in the pentose phosphate pathway such as Ribose-5-phosphate isomerase A as well as proteins associated with sugar transport systems were upregulated indicating enhanced carbohydrate metabolism. Interestingly mixed-species biofilm microenvironment had a lower pH than S. mutans single-species biofilms. This observation was supported by proteomics, wherein proteins associated with lactate and formate assimilation such as Glyoxalase and putative NADPH-dependent methylglyoxal reductase proteins were significantly upregulated in the mixed-species biofilms (P<0.05). Furthermore, we unexpectedly found that S. mutans derived glucosyltransferase B (GtfB), responsible for co-adhesion via glucans, can also contribute to C. albicans growth and carbohydrate metabolism by providing glucose and fructose from sucrose breakdown. These findings demonstrate synergistic bacterial-fungal interactions within mixed-species biofilms and a novel GtfB cross-feeding role. Taken together, quantitative proteomics provides new insights into this virulent cross-kingdom oral biofilm.

Project description:Polymicrobial biofilms are of large medical importance, but little is known about their physiology and the underlying interspecies interactions. Here we studied two human pathogens, the opportunistic fungus Candida albicans and the caries promoting bacterium Streptococcus mutans. Both species formed biofilms in monoculture, with C. albicans growing mainly in the virulence-associated hyphae form, and S. mutans forming a thick layer of extracellular polymeric substances (EPS). Biofilm growth was enhanced in dual-species biofilms, which reached twice the biomass of monospecies biofilms and higher cell numbers of both S. mutans and C. albicans. EPS production by S. mutans was strongly suppressed in dual-species biofilms. Virulence traits of S. mutans, e.g. genetic competence, biofilm formation and bacteriocin synthesis are controlled by quorum sensing through activation of the alternative sigma factor SigX. SigX is induced by the pheromones CSP (competence stimulating factor) or XIP (sigX inducing peptide). Strong induction of sigX was observed in dual species biofilms indicated by fluorescence of a reporter strain for the sigX promoter, S. mutans PcomX-gfp, as well as by qRT-PCR of comX. The peak of sigX expression occurred after 10 h of biofilm growth. Conditioned media from mixed biofilms but not from C. albicans or S. mutans cultivated alone activated sigX in the reporter strain. Deletion mutants for the comC and comS genes encoding the precursors of CSP and XIP, respectively, were constructed. Conditioned media from mixed biofilms with S. mutans DcomS were unable to induce sigX in the reporter strain, while deletion of comC had no effect. These data show that synthesis of XIP was induced in S. mutans by coculture with C. albicans. Transcriptome analysis of S. mutans in single and mixed biofilms confirmed strong induction of comS, sigX, and the downstream late competence genes in dual-species biofilms. Among the late competence genes, fratricins were discovered for the first time. The comCDE operon and bacteriocin related genes were also induced, but much weaker. Genes related to oxidative stress, chaperones and glycosyltransferase genes required for EPS synthesis from sucrose were down-regulated, while glycogen synthesis genes were up-regulated, indicating that S. mutans was protected from oxidative stress and provided with excess sugar for storage polymer synthesis in mixed biofilms. The data show that in dual-species biofilms, C. albicans improves growth of S. mutans, suppresses its EPS formation and induces the complete quorum sensing signalling system, thus fundamentally changing the virulence properties of the caries pathogen, including its potential interactions with other members of the polymicrobial dental plaque community. Dual-species biofilms of S. mutans and C. albicans and single-species biofilms of S. mutans were cultivated in 24-well microtitre plates in YNBB medium. Transcriptional profiles of S. mutans in single- and dual-species biofilms were analysed at early (6 h) and late (10 h) logarithmic phase of the biofilm growth, as well as after 24 h when biofilms entered stationary phase. Transcriptional profiles of S. mutans grown in the dual-species biofilms were compared to profiles obtained for single-species biofilm from the same time point. Three biological and one to two technical replicas were used in the microarray study. RNA samples were labeled with Cy3 or Cy5 using the ULS fluorescent labeling kit (Kreatech, Germany). Seven hundred nanograms of Cy3 or Cy5 labeled RNA after fragmentation were hybridized to the microarray at 65M-BM-0C for 17 h using the Agilent hybridization chamber according to the manufacturer's instructions. The arrays were scanned using the Agilent DNA microarray scanner and the raw data were extracted using Agilent Feature Extraction software (v. 10.7).

Project description:Biofilms are a communal of one or several kinds of microorganisms that growing on of both non-living and biotic surfaces by the production of multi-layers high-abundance extracellular matrix (ECM) to survive in the harsh environments (1-4). Biofilms consist of 85% (by volume) of matrix materials and 15% microbial cells (5). Biofilm ECM, consists of proteins, polysaccharides and/or extracellular DNAs, is important for biofilm integrity that increases environmental adaptability and induces antimicrobial resistance (6-7). Surface-adherent (sessile) bacteria in biofilms are more difficult to eradicate as minimum inhibitory concentrations (MICs) of antibiotics against bacterial biofilms is 100-1000 folds higher than the free living (planktonic) form that resulting in recurrent infections (8). Biofilms also possibly form nidus at the surface for the attachment of other pathogens lead to biofilms of multiple bacteria or multi-organisms (9ref). The communication, among organisms within biofilm, controls density of cell population refers to as “quorum sensing” (10) and different combinations of organisms in biofilms with either multiple bacteria or multi-species might induce different biofilm properties. While catheter-related colonization of Gram-positive bacteria from skin microbiota such as Streptococcus spp. and Staphylococcus spp. is common, biofilms in the inner lumen of catheter consist of both Gram-positive and Gram-negative bacteria. Because i) translocation of gut microbiota (eg. Enterococcus spp., Gram-negative bacteria and Candida albicans) into blood circulation during sepsis is one of the common causes of severe sepsis , ii) mixed systemic infection between bacteria and Candida spp. is even more severe than the infection by each organism in separation and iii) biofilms could be formed during bacteremia and fungemia, the biofilms from mixed species between bacteria and Candida spp. during sepsis is possible. In addition, central venous catheter-related candidiasis is common in intensive care units (ICU) patients refer to as “Candida catheter-related bloodstream infection (CRCBSI)”. Moreover, synergistic interaction between Candida albicans and several Gram-negative bacteria such as Escherichia coli (in peritonitis), Pseudomonas aeruginosa (in cystic fibrosis and ventilation associated pneumonia) and Acinetobacter baumannii (in ventilation associated pneumonia) has been mentioned. Hence, the collaboration between bacteria and Candida spp. might affect biofilm production as C. albicans in coexistence with the sessile microbes possibly enhance biofilms production that is detectable by crystal violet color (16,7). It is interesting to note that C. albicans are normal microbiota in human intestine and gut-translocation from intestine into blood circulation during severe sepsis (gut leakage) is demonstrated. Furthermore, both Gram-negative bacteria and C. albicans are the most and the second most predominant intestinal human microbiota, respectively, in which the natural interactions between these organisms is possible. Accordingly, catheter-related bacteremia is common among patients in ICU. Gut translocation of Candida spp. during sepsis, due to gut leakage, might induce the collaboration between bacteria and fungi results in persistent infection (20-21Chen L, 2011, 66//Wu H, 2015, 1, IJOS). Although the understanding in the interaction between organisms in biofilms should be beneficial for eradication strategies, the data of biofilms from the combination between gut-derived bacteria and fungi is still limited. As such, production of exo-polymers for biofilm-forming is a pathogenic virulent factor because biofilms is one of the important defend-mechanisms against host immune responses and antibiotics. Because i) antibiotic resistance caused by biofilm is a current serious medical problem , ii) the eradication of both bacterial and fungal biofilms is difficult and iii) antimicrobial treatment without biofilms-removal resulting in recurrent or persistent infection (23ref), biofilm prevention agent is needed (2410). Here, we explored i) the interaction between Gram-negative bacteria and C. albicans, in vitro, ii) macrophage responses against biofilm components, iii) biofilms in catheter-insertion mouse model and an evaluation on an interesting anti-biofilm.

Project description:Polymicrobial biofilms are of large medical importance, but little is known about their physiology and the underlying interspecies interactions. Here we studied two human pathogens, the opportunistic fungus Candida albicans and the caries promoting bacterium Streptococcus mutans. Both species formed biofilms in monoculture, with C. albicans growing mainly in the virulence-associated hyphae form, and S. mutans forming a thick layer of extracellular polymeric substances (EPS). Biofilm growth was enhanced in dual-species biofilms, which reached twice the biomass of monospecies biofilms and higher cell numbers of both S. mutans and C. albicans. EPS production by S. mutans was strongly suppressed in dual-species biofilms. Virulence traits of S. mutans, e.g. genetic competence, biofilm formation and bacteriocin synthesis are controlled by quorum sensing through activation of the alternative sigma factor SigX. SigX is induced by the pheromones CSP (competence stimulating factor) or XIP (sigX inducing peptide). Strong induction of sigX was observed in dual species biofilms indicated by fluorescence of a reporter strain for the sigX promoter, S. mutans PcomX-gfp, as well as by qRT-PCR of comX. The peak of sigX expression occurred after 10 h of biofilm growth. Conditioned media from mixed biofilms but not from C. albicans or S. mutans cultivated alone activated sigX in the reporter strain. Deletion mutants for the comC and comS genes encoding the precursors of CSP and XIP, respectively, were constructed. Conditioned media from mixed biofilms with S. mutans DcomS were unable to induce sigX in the reporter strain, while deletion of comC had no effect. These data show that synthesis of XIP was induced in S. mutans by coculture with C. albicans. Transcriptome analysis of S. mutans in single and mixed biofilms confirmed strong induction of comS, sigX, and the downstream late competence genes in dual-species biofilms. Among the late competence genes, fratricins were discovered for the first time. The comCDE operon and bacteriocin related genes were also induced, but much weaker. Genes related to oxidative stress, chaperones and glycosyltransferase genes required for EPS synthesis from sucrose were down-regulated, while glycogen synthesis genes were up-regulated, indicating that S. mutans was protected from oxidative stress and provided with excess sugar for storage polymer synthesis in mixed biofilms. The data show that in dual-species biofilms, C. albicans improves growth of S. mutans, suppresses its EPS formation and induces the complete quorum sensing signalling system, thus fundamentally changing the virulence properties of the caries pathogen, including its potential interactions with other members of the polymicrobial dental plaque community.

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Genetic Insights into the Rheological Strength of Candida albicans Biofilms

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