Functional analysis of bacterial reverse transcriptase genes and retroelements in pathogenic bacteria

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Bacterial reverse transcriptase is responsible for the synthesis of satellite RNA-DNA complex called multicopy single-stranded DNA(msDNA). A genetic element required for the msDNA synthesis is named retron which consists of the msr-msd region, a coding region for the msDNA and the ret gene, a coding region for reverse transcriptase. Although the role(s) of retron and msDNA remains unclear, it has been reported that mutation frequency was increased in Escherichia coli under conditions in which msDNA was overproduced in a cell.To date, we have demonstrated the existence of msDNA in pathogenic bacteria, such as Vibrio cholerae, V.parahaemolyticus, and so on, and cloned the retron regions from their chromosomes. A relationship between msDNA and/or reverse transcriptase and bacterial pathogenicity has been suggested recently. A major purpose of this study is to investigate the relationship between msDNA and/or reverse transcriptase and pathogenicity in pathogenic bacteria.In this study, differential gene expression between wild-type V.cholerae and a ret gene mutant was examined by microarray analysis. It was found that virulence genes, such as the cholera toxin genes (ctxAB), the intestinal colonization factor gene (tcpA), ompU, and so on, were highly expressed in the ret mutant, suggesting that the msDNA and/or reverse transciptase is involved in regulation of those virulence genes in V.cholerae.A novel msDNA, msDNA-St85, from Salmonella enterica serovar Typhimurium was isolated and characterized. It was found that the G+C content and the codon usage of retron-St85 were significantly different from those of the S.Typhimurium genome, indicating that retron-St85 was probably acquired recently in this bacterium.