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: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.

Project description:The interaction of clinically relevant microorganisms is the focus of various studies, e.g. the interaction between the pathogenic yeast, Candida albicans, and the bacterium, Pseudomonas aeruginosa and these interactions can alter the outcome of infection, growth dynamics of each species and antimicrobial resistance of pathogens. During infection, both C. albicans and P. aeruginosa can elicit the release arachidonic acid (AA) from host cells membranes through the action of phospholipases. This polyunsaturated fatty acid can be transformed into immune-modulating compounds, termed eicosanoids, by both host-derived and microbial-derived enzymatic reactions. In its free form, AA can affect the growth of both C. albicans and P. aeruginosa, inhibiting the morphogenesis of C. albicans as well as reducing resistance towards antifungal agents. However, the mechanism of this is unknown. Previous studies on the effect of polyunsaturated fatty acids have indicated a possible alteration in plasma membrane organisation and permeability. Our group aimed to address how AA affects C. albicans in both single species biofilms, as well as in polymicrobial biofilms with P. aeruginosa. RNAseq was performed on single and polymicrobial biofilms in the presence and absence of a sub-inhibitory (100 µM) concentration of AA. Differential expression was determined between C. albicans single species biofilms in the presence and absence of AA. Secondly, the influence of co-incubation of C. albicans with P. aeruginosa in the absence of AA was evaluated to identify novel facets of interaction not previously identified, and to establish a baseline to determine the effect of AA on C. albicans in polymicrobial biofilms. Lastly, the effect of AA on C. albicans in polymicrobial biofilms was determined through comparison with polymicrobial biofilms in the absence of AA. This study provides a comprehensive analysis of the effect of AA and both co-incubation of C. albicans with P. aeruginosa focused on the transcriptome.

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Transcriptomic analysis of bacterial vaginosis-associated bacteria living in single or multispecies biofilms

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