Project description:BACKGROUND: Hundreds of bacterial species coexist within the human oral cavity, where complex interactions can occur. Recent evidence has shown that the commensal oral streptococci that populate supragingival biofilms on the tooth surface produce extracellular proteases that degrade cell-cell signaling molecules of their disease-causing competitors, Streptococcus mutans. To further explore these interactions, we performed transcriptome analysis of S. mutans cocultured with different oral streptococci and found that cell-cell signaling was complety inhibited, but only when the bacteria were directly cocultured together. METHODS: RNA-Seq was utilized to compare the transcriptomes of S. mutans wild-type strain UA159 cocultured in its own supernatant (3 replicates), UA159 cocultured in S. sp. A12 supernatant (3 replicates) and directly cocultured with S. sp. A12 (3 replicates). Strains were grown to OD600 nm = 0.5 in CDM medium before harvest. Deep sequencing was performed at the University of Florida ICBR facilities (Gainesville, FL). Approximately 15 million short-reads were obtained for each sample. After removing adapter sequences from each short-read and trimming of the 3’-ends by quality scores, the resulting sequences were mapped onto the reference genome of strain UA159 (GenBank accession no. AE014133) using the short-read aligner. Mapped short-read alignments were then converted into readable formats using SAMTOOLS. RESULTS: Using an optimzed data analysis workflow, we mapped 13-16 million reads per sample to the genome of UA159. For viewing of the mapped reads aligned to the genome, .bam files were uploaded into the Integrative Genomics Viewer (IGV – version 2.3.55). A .csv file containing raw read counts for each replicate (3) was then uploaded to Degust (http://degust.erc.monash.edu/) and edgeR analysis performed to determine Log2 fold change and a false discovery rate (FDR). When comparing the growth of S. mutans in its own spent supernatant against competitor spent supernatants, we found 88 genes differentially expressed (Log2 fold change > (-)1.5, -log10 P-value > 4) which included upregulation of the zinc transport system and several amino acid ABC transporters, along with downregulation of the TnSmu1 genomic island. A more substantial effect was seen when we compared growth of S. mutans in competitor spent supernatant compared to growth directly with a competitor. Here, 140 genes were differentially expressed and included upregulation of one of the CRISPR genetic clusters as well as downregulation of the entire genetic competence regulon, as expected. Principal component analysis (PCA) of transcriptome data from these three conditions displayed a wide variation and separation among the tested groups, further confirming a unique transcriptome response for S. mutans between growth in the supernatant of a competitor and directly with a competitor. CONCLUSIONS: We believe that these measured transcriptomic changes represent a conserved S. mutans response to competitors that has not been previously captured in RNA-Seq experiments of monocultures alone. Together, these results highlight a previously undocumented transcriptomic alteration by S. mutans when challenged by health-associated oral streptococci.

Project description:BACKGROUND: Streptococcus mutans, the etiological agent of human dental caries, displays complex regulation of natural genetic competence. Competence development in S. mutans is controlled by a peptide derived from ComS (comX inducing peptide, XIP); which along with the cytosolic regulator ComR controls the expression of the alternative sigma factor comX, the master regulator of competence development. ComR-XIP controls the expression of both PcomX and PcomS, with the latter creating a positive feedback loop. Recently, a gene embedded within the coding region of comX was discovered and designated xrpA (comX regulatory peptide A). XrpA was found to be an antagonist of ComX, but the mechanism was not established. In this study, we began to dissect how XrpA exerts control over competence development in S. mutans. METHODS: RNA-Seq was utilized to compare the transcriptomes of S. mutans wild-type strain UA159 (3 replicates), UA159 with addition of 2 uM sXIP (3 replicates) and with a mutant of xrpA (comX::T162C; 3 replicates). Strains were grown to OD600 nm = 0.5 in FMC medium before harvest. sXIP was added at OD600 nm = 0.2. Deep sequencing was performed at the University of Florida ICBR facilities (Gainesville, FL). Approximately 20 million short-reads were obtained for each sample. After removing adapter sequences from each short-read and trimming of the 3’-ends by quality scores (59), the resulting sequences were mapped onto the reference genome of strain UA159 (GenBank accession no. AE014133) using the short-read aligner. Mapped short-read alignments were then converted into readable formats using SAMTOOLS. RESULTS: Using an optimzed data analysis workflow, we mapped 14-19 million reads per sample to the genome of UA159. For viewing of the mapped reads aligned to the genome, .bam files were uploaded into the Integrative Genomics Viewer (IGV – version 2.3.55) (61). A .csv file containing raw read counts for each replicate (3) was then uploaded to Degust (http://degust.erc.monash.edu/) and edgeR analysis performed to determine Log2 fold change and a false discovery rate (FDR). Comparison of the transcriptome by RNA-Seq of the wild-type with the mutant lacking XrpA revealed 56 differentially expressed genes, with 34 upregulated in xrpA and 22 downregulated. Many of the upregulated genes were competence-related genes, including comX and genes that are a part of the ComX regulon of S. mutans . Since loss of xrpA caused upregulation of competence genes, we also analyzed the transcriptome of UA159 treated with 2 uM sXIP to induce competence, with UA159 treated with vehicle (DMSO) as a control. Cells treated with sXIP had 137 genes differentially expressed compared to the DMSO control. CONCLUSIONS: Collectively, these data reveal that the novel regulator XrpA exerts its influence over competence development by impacting ComRS functions, resulting in decreased expression of comX and late com gene expression that negatively impact transformability. These results highlight XrpA as a new negative regulator of competence signaling as well as broaden our understanding of the complex regulatory mechanisms that modulate competence and virulence in S. mutans.

Project description:BACKGROUND: While substantial advances have been made to understand the nature and significance of interspecies interaction in oral microbial communities, much remains to be learned about how commensal species contribute to the maintenance of health-associated biofilm communities. We report that successful competition of Streptococcus sp. A12 with the dental pathogen Streptococcus mutans requires many different factors. While A12 can directly inhibit the growth of S. mutans, A12 harbors several genes (i.e. pcfFEGRK) that are required to be able to tolerate antagonistic factors of S. mutans, and these gene products are critical to the competitive fitness of A12. Here, we delve deeper in the role of the pcfFEG, a predicted lantibiotic immunity transporter, and the pcfRK, its genetically-linked two-component system (TCS) in A12. METHODS: RNA-Seq was utilized to compare the transcriptomes of A12 wild-type strain and A12 lacking the response regulator (pcfR) or histidine kinase (pcfK) of pcfRK, a TCS directly regulating pcfFEG. Each strains were prepared in 3 biological replicates. Strains were grown to OD600 nm = 0.4 in BHI medium before harvest. Deep sequencing was performed at the University of Florida ICBR facilities (Gainesville, FL). Approximately 15 million short-reads were obtained for each sample. After removing adapter sequences from each short-read and trimming of the 3’-ends by quality scores, the resulting sequences were mapped onto the reference genome of strain Streptococcus sp. A12 (NCBI Reference Sequence: NZ_CP013651.1) using the short-read aligner. Mapped short-read alignments were then converted into readable formats using SAMTOOLS. RESULTS: Using an optimized data analysis workflow, we mapped 13-16 million reads per sample to the genome of A12. For viewing of the mapped reads aligned to the genome, .bam files were uploaded into the Integrative Genomics Viewer (IGV – version 2.3.55). A .csv file containing raw read counts for each replicate (3) was then uploaded to Degust (http://degust.erc.monash.edu/) and edgeR analysis performed to determine Log2 fold change and a false discovery rate (FDR). When compared to the wild-type A12 strain, 61 genes were differentially expressed in A12 lacking pcfR and 35 genes were differentially expressed in A12 lacking pcfK (Log2 fold change > (-)1.5, -log10 P-value > 4). Interestingly, a subset of the same genes was found to be upregulated in both pcfR and pcfK deletion strains, including ATM98_04215, ATM98_04220 and ATM98_03625, annotated as a protease, a dipeptidase (both co-transcribed), and an aminopeptidase, respectively. Another interesting finding was a cluster of genes predicted to be the mannose PTS system was downregulated in the pcfK mutant strain, and a two-component ABC transporter annotated as ABC-type CcmA multidrug resistance system was found to be upregulated in the pcfR mutant strain. The pcfK mutant strain showed an upregulation of the pcfFEG genes and the cognate response regulator gene, pcfR. In the pcfR mutant, pcfK was also upregulated, compared to the parental A12 strain. CONCLUSIONS: Transcriptional profiling of pcfR and pcfK mutant strains revealed the scope of the pcfRK regulon. When supplemented with functional genomics, we uncovered additional genes shown to function independently or cooperatively with PcfFEGRK in tolerating the lantibiotic nisin. Together these results highlight additional mechanisms beneficial species may be utilizing to remain competitive when existing in complex microbial communities.

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