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Gene expression profiling of constitutively competent comR and proQ mutants and RNase R (rnr) mutant of L. pneumophila

ABSTRACT: Bacterial competence is a genetically programmed process that is triggered as a response to environmental stimuli. DNA uptake from the extracellular milieu by competence requires the expression of a complex machinery composed of a competence pseudopilus and a DNA translocase. In L. pneumophila, it has been reported that microaerophilic conditions and genetic alteration of the competence repressors ComR and ProQ result in competence. We have analyzed the gene expression profiles of the proQ and comR mutants using the L. pneumophila Philadelphia-1 microarray. Many competence genes were found to be induced in the comR and proQ mutants and represent a defined, regulon. The gene expression profiling of the proQ and comR mutants was part of a study aimed at understanding the function of the processive 3'-5' exoribonuclease RNase R (rnr gene) in L. pneumophila. We found that the gene expression profile of the rnr mutant shares similarities with the gene expression profiles of the comR and proQ mutants and that loss of the exoribonuclease activity of RNase R was sufficient to induce competence development. RNase R is a processive 3'-5' exoribonuclease with a high degree of conservation in prokaryotes. Although some bacteria possess additional hydrolytic 3´-5-exoribonucleases such as RNase II, RNase R was found to be the only one predicted in the Legionella pneumophila genome. This provided a unique opportunity to study the role of RNase R in the absence of an additional RNase with similar enzymatic activity. We investigated the role of RNase R in the biology of Legionella pneumophila under various conditions and performed gene expression profiling using microarrays. At optimal growth temperature, loss of RNase R had no major consequence on bacterial growth and had a moderate impact on normal gene regulation. However, at lower temperatures loss of RNase R has a significant impact on bacterial growth and resulted in the accumulation of structured RNA degradation products. Concurrently, gene regulation was affected and specifically resulted in increased expression of the competence regulon. Loss of the exoribonuclease activity of RNase R was sufficient to induce competence development, a genetically-programmed process normally triggered as a response to environmental stimuli. Temperature-dependent expression of competence genes in the rnr mutant was found to be independent of the previously identified competence regulators comR and ProQ.

ORGANISM(S): Legionella pneumophila subsp. pneumophila str. Philadelphia 1 Legionella pneumophila

PROVIDER: GSE12796 | GEO | 2008/09/18

SECONDARY ACCESSION(S): PRJNA110987

REPOSITORIES: GEO

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Project description:Bacterial competence is a genetically programmed process that is triggered as a response to environmental stimuli. DNA uptake from the extracellular milieu by competence requires the expression of a complex machinery composed of a competence pseudopilus and a DNA translocase. In L. pneumophila, it has been reported that microaerophilic conditions and genetic alteration of the competence repressors ComR and ProQ result in competence. We have analyzed the gene expression profiles of the proQ and comR mutants using the L. pneumophila Philadelphia-1 microarray. Many competence genes were found to be induced in the comR and proQ mutants and represent a defined, regulon. The gene expression profiling of the proQ and comR mutants was part of a study aimed at understanding the function of the processive 3'-5' exoribonuclease RNase R (rnr gene) in L. pneumophila. We found that the gene expression profile of the rnr mutant shares similarities with the gene expression profiles of the comR and proQ mutants and that loss of the exoribonuclease activity of RNase R was sufficient to induce competence development. RNase R is a processive 3'-5' exoribonuclease with a high degree of conservation in prokaryotes. Although some bacteria possess additional hydrolytic 3Â´-5-exoribonucleases such as RNase II, RNase R was found to be the only one predicted in the Legionella pneumophila genome. This provided a unique opportunity to study the role of RNase R in the absence of an additional RNase with similar enzymatic activity. We investigated the role of RNase R in the biology of Legionella pneumophila under various conditions and performed gene expression profiling using microarrays. At optimal growth temperature, loss of RNase R had no major consequence on bacterial growth and had a moderate impact on normal gene regulation. However, at lower temperatures loss of RNase R has a significant impact on bacterial growth and resulted in the accumulation of structured RNA degradation products. Concurrently, gene regulation was affected and specifically resulted in increased expression of the competence regulon. Loss of the exoribonuclease activity of RNase R was sufficient to induce competence development, a genetically-programmed process normally triggered as a response to environmental stimuli. Temperature-dependent expression of competence genes in the rnr mutant was found to be independent of the previously identified competence regulators comR and ProQ. comR: Three test samples and three reference samples were analyzed. The test sample being the strain KS79, a comR mutant of L. pneumophila strain JR32 which is used as a reference. proQ: Three test samples and three reference samples were analyzed. The test sample being the strain LELA3825, a proQ mutant of L. pneumophila strain JR32 which is used as a reference. rnr: Six test samples and six reference samples grown at 30Â°C or 37Â°C were analyzed. The test sample being the strain LELA559, a rnr mutant of L. pneumophila strain JR32 which is used as a reference.

Project description:Background The RNA steady-state levels in the cell are a balance between synthesis and degradation rates. Although transcription is important, RNA processing and turnover are also key factors in the regulation of gene expression. In Escherichia coli there are three main exoribonucleases (RNase II, RNase R and PNPase) involved in RNA degradation. Although there are many studies about these exoribonucleases not much is known about their global effect in the transcriptome. Results In order to study the effects of the exoribonucleases on the transcriptome, we sequenced the total RNA (RNA-Seq) from wild-type cells and from mutants for each of the exoribonucleases (∆rnb, ∆rnr and ∆pnp). We compared each of the mutant transcriptome with the wild-type to determine the global effects of the deletion of each exoribonucleases in exponential phase. We determined that the deletion of RNase II significantly affected 187 transcripts, while deletion of RNase R affects 202 transcripts and deletion of PNPase affected 226 transcripts. Surprisingly, many of the transcripts are actually down-regulated in the exoribonuclease mutants when compared to the wild-type control. The results obtained from the transcriptomic analysis pointed to the fact that these enzymes were changing the expression of genes related with flagellum assembly, motility and biofilm formation. The three exoribonucleases affected some stable RNAs, but PNPase was the main exoribonuclease affecting this class of RNAs. We confirmed by qPCR some fold-change values obtained from the RNA-Seq data, we also observed that all the exoribonuclease mutants were significantly less motile than the wild-type cells. Additionally, RNase II and RNase R mutants were shown to produce more biofilm than the wild-type control while the PNPase mutant did not form biofilms. Conclusions In this work we demonstrate how deep sequencing can be used to discover new and relevant functions of the exoribonucleases. We were able to obtain valuable information about the transcripts affected by each of the exoribonucleases and compare the roles of the three enzymes. Our results show that the three exoribonucleases affect cell motility and biofilm formation that are two very important factors for cell survival, especially for pathogenic cells.

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Gene expression profiling of constitutively competent comR and proQ mutants and RNase R (rnr) mutant of L. pneumophila

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