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: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.

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Legionella pneumophila

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