Project description:Plant-released flavonoids induce the transcription of symbiotic genes in rhizobia and one of the first bacterial responses is the synthesis of so called Nod factors. They are responsible for the initial root hair curling during onset of root nodule development. This signal exchange is believed to be essential for initiating the plant symbiosis with rhizobia affiliated with the alphaproteobacteria. Here, we provide evidence that in broad host range rhizobia the complete lack of quorum sensing molecules results in an elevated copy number of its symbiotic plasmid (pNGR234a). This in turn triggers the expression of symbiotic genes and the production of Nod factors in the absence of plant signals. Therefore, increasing the copy number of specific plasmids could be a widespread mechanism of specialized bacterial populations bridging gaps in signalling cascades and providing a competitive advantage.
Project description:RNA-seq in the broad host range strain Sinorhizobium fredii NGR234 identifies a large set of genes linked to quorum sensing-dependent regulation in the background of a traI and ngrI deletion mutant
Project description:The α-proteobacterium Sinorhizobium fredii NGR234 has an exceptionally wide host range as it forms nitrogen-fixing nodules with more legumes than any other known microsymbiont. Within its 6.9 Mbp genome it encodes two N-acyl-homoserine-lactone synthase genes (i.e. traI and ngrI) involved in the biosynthesis of two distinct autoinducer I-type molecules. Here we report on the construction of a NGR234-ΔtraI and a NGR234-ΔngrI mutant and the genome wide RNA-seq-based transcriptome analysis in the parent strain and in the two constructed mutants. A high-resolution RNA-seq analysis of early stationary phase cultures in the background of NGR234-ΔtraI suggested that up to 316 genes (4.9% of all predicted genes) were differentially expressed in the mutant vs. the parent strain. Similarly, in the background of NGR234-ΔngrI 466 differentially regulated genes (7.3% of all predicted genes) were identified. A considerable overlap in the gene expression pattern was uncovered between both mutants resulting in a common set of 186 genes which were almost identically regulated. Co-regulated genes that were linked to the ngrI- and the traI-dependent autoinducer regulatory circuits included 53 flagella biosynthesis genes and genes linked to EPS succinoglycan biosynthesis. Among the genes and ORFs that were differentially regulated in NGR234-ΔtraI were those linked to replication of the pNGR234a symbiotic plasmid and cytochrome c-related genes. In the NGR234-ΔngrI mutant biotin and pyrroloquinoline quinone (PQQ) biosynthesis genes were differentially expressed as well as the entire cluster of 21 genes linked to assembly of the NGR234 type three secretion system II (T3SS-II). We also discovered that genes responsible for octopine catabolism in NGR234 are strongly repressed in the presence of high levels of N-acyl-homoserine-lactones (AHLs). Surprisingly, only few truly symbiosis-related genes were identified that appeared to be quorum sensing regulated. Together with nodulation assays, the RNAseq-based findings suggested that QS-dependent gene regulation appears to be of higher relevance during non-symbiotic growth rather than for life within root nodules.
Project description:The M-NM-1-proteobacterium Sinorhizobium fredii NGR234 has an exceptionally wide host range as it forms nitrogen-fixing nodules with more legumes than any other known microsymbiont. Within its 6.9 Mbp genome it encodes two N-acyl-homoserine-lactone synthase genes (i.e. traI and ngrI) involved in the biosynthesis of two distinct autoinducer I-type molecules. Here we report on the construction of a NGR234-M-NM-^TtraI and a NGR234-M-NM-^TngrI mutant and the genome wide RNA-seq-based transcriptome analysis in the parent strain and in the two constructed mutants. A high-resolution RNA-seq analysis of early stationary phase cultures in the background of NGR234-M-NM-^TtraI suggested that up to 316 genes (4.9% of all predicted genes) were differentially expressed in the mutant vs. the parent strain. Similarly, in the background of NGR234-M-NM-^TngrI 466 differentially regulated genes (7.3% of all predicted genes) were identified. A considerable overlap in the gene expression pattern was uncovered between both mutants resulting in a common set of 186 genes which were almost identically regulated. Co-regulated genes that were linked to the ngrI- and the traI-dependent autoinducer regulatory circuits included 53 flagella biosynthesis genes and genes linked to EPS succinoglycan biosynthesis. Among the genes and ORFs that were differentially regulated in NGR234-M-NM-^TtraI were those linked to replication of the pNGR234a symbiotic plasmid and cytochrome c-related genes. In the NGR234-M-NM-^TngrI mutant biotin and pyrroloquinoline quinone (PQQ) biosynthesis genes were differentially expressed as well as the entire cluster of 21 genes linked to assembly of the NGR234 type three secretion system II (T3SS-II). We also discovered that genes responsible for octopine catabolism in NGR234 are strongly repressed in the presence of high levels of N-acyl-homoserine-lactones (AHLs). Surprisingly, only few truly symbiosis-related genes were identified that appeared to be quorum sensing regulated. Together with nodulation assays, the RNAseq-based findings suggested that QS-dependent gene regulation appears to be of higher relevance during non-symbiotic growth rather than for life within root nodules. In total 12 samples were analyzed (six different treatments with two independent samples), treatment A: NGR234 wild type strain in stationary phase, treatment B: NGR234 traI-mutant strain in stationary phase, treatment C: NGR234 ngrI-mutant strain in stationary phase, treatment D: NGR234 wild type strain in exponential phase, treatment E: NGR234 wild type supplemented with 0.05 M-BM-5M AHLs in exponential phase, treatment F: NGR234 wild type supplemented with 50 M-BM-5M AHLs in exponential phase
Project description:Yersinia pestis, the etiological agent of plague, is able to sense cell density by quorum sensing. The function of quorum sensing in Y. pestis is not clear. Here, the process of quorum sensing was investigated by comparing transcript profiles when three quorum-sensing signals are added in. The strain ∆pgm (pigmentation-negative) mutant R88 was used as wild type. The three signals are AI-2, AHLs (N-(3-Oxooctanoyl)-L-homoserine lactone and N-Hexanoyl-DL-homoserine lactone).The control consisted of cells grown and treated under the same conditions without added signals.
Project description:Yersinia pestis, the etiological agent of plague, is able to sense cell density by quorum sensing. The function of quorum sensing in Y. pestis is not clear. Here, the process of AHL quorum sensing was investigated by comparing transcript profiles when two AHL quorum-sensing signals are added in. The strain Δpgm (pigmentation-negative) mutant was called wild type. The two AHLs signals are N-(3-Oxooctanoyl)-L-homoserine lactone and N-Hexanoyl-DL-homoserine lactone.The control consisted of cells grown and treated under the same conditions without added signals.
Project description:Yersinia pestis, the etiological agent of plague, is able to sense cell density by quorum sensing. The function of quorum sensing in Y. pestis is not clear. Here, the process of AHL quorum sensing was investigated by comparing transcript profiles when two AHL quorum-sensing signals are added in. The strain ∆pgm (pigmentation-negative) mutant R88 was called wild type. The two AHLs signals are N-(3-Oxooctanoyl)-L-homoserine lactone and N-Hexanoyl-DL-homoserine lactone.The control consisted of cells grown and treated under the same conditions without added signals.
Project description:Quorum sensing is a term used to describe cell-to-cell communication that allows cell density-dependent gene expression. Many Gram-negative bacteria use acyl-homoserine lactone (acyl-HSL) synthases to generate fatty acyl-HSL quorum sensing signals, which function with signal receptors to control expression of specific genes. The fatty acyl group is derived from fatty acid biosynthesis and provides signal specificity, but the variety of signals is limited. We have discovered that the photosynthetic bacterium Rhodopseudomonas palustris uses an acyl-HSL synthase to produce p-coumaroyl-HSL by using environmental p-coumaric acid rather than fatty acids from cellular pools. The bacterium has a signal receptor with homology to fatty acyl-HSL receptors that responds to p-coumaroyl-HSL to regulate global gene expression. We also found that p-coumaroyl-HSL is made by other bacteria including Bradyrhizobium BTAi1 and Silicibacter pomeroyi DSS-3. This discovery extends the range of possibilities for acyl-HSL quorum sensing and raises fundamental questions about quorum sensing within the context of environmental signaling. Keywords: Comparison of transcriptome profiles Transcriptome profiles between Rhodopseudomonas palustris cells grown in the in the presence or absence of pC-HSL were compared.
Project description:Quorum sensing is a term used to describe cell-to-cell communication that allows cell density-dependent gene expression. Many Gram-negative bacteria use acyl-homoserine lactone (acyl-HSL) synthases to generate fatty acyl-HSL quorum sensing signals, which function with signal receptors to control expression of specific genes. The fatty acyl group is derived from fatty acid biosynthesis and provides signal specificity, but the variety of signals is limited. We have discovered that the photosynthetic bacterium Rhodopseudomonas palustris uses an acyl-HSL synthase to produce p-coumaroyl-HSL by using environmental p-coumaric acid rather than fatty acids from cellular pools. The bacterium has a signal receptor with homology to fatty acyl-HSL receptors that responds to p-coumaroyl-HSL to regulate global gene expression. We also found that p-coumaroyl-HSL is made by other bacteria including Bradyrhizobium BTAi1 and Silicibacter pomeroyi DSS-3. This discovery extends the range of possibilities for acyl-HSL quorum sensing and raises fundamental questions about quorum sensing within the context of environmental signaling. Keywords: Comparison of transcriptome profiles