Abstract
The genes for DNA uptake and recombination in Bacilli are commonly regulated by the transcriptional factor ComK. We have identified a ComK homologue in Bacillus coagulans, an industrial relevant organism that is recalcitrant for transformation. Introduction of B. coagulans comK gene under its own promoter region into Bacillus subtilis comK strain results in low transcriptional induction of the late competence gene comGA, but lacking bistable expression. The promoter regions of B. coagulans comK and the comGA genes are recognized in B. subtilis and expression from these promoters is activated by B. subtilis ComK. Purified ComK protein of B. coagulans showed DNA-binding ability in gel retardation assays with B. subtilis- and B. coagulans-derived probes. These experiments suggest that the function of B. coagulans ComK is similar to that of ComK of B. subtilis. When its own comK is overexpressed in B. coagulans the comGA gene expression increases 40-fold, while the expression of another late competence gene, comC is not elevated and no reproducible DNA-uptake could be observed under these conditions. Our results demonstrate that B. coagulans ComK can recognize several B. subtilis comK-responsive elements, and vice versa, but indicate that the activation of the transcription of complete sets of genes coding for a putative DNA uptake apparatus in B. coagulans might differ from that of B. subtilis.
Highlights
The ability to take-up DNA from the environment is widely spread among eubacteria, including Gram-positive and Gramnegative species [1]
DSM 1, 36D1 and 2–6 showed that several genes and operons can be identified with high sequence similarity to Bacillus genes that code for the late competence genes in B. subtilis and their homologues in other Bacillus species (Fig. 1A)
The genomes of all B. coagulans species lack the nucA-nin operon that is required for the DNA cleavage during transformation in B. subtilis [46]
Summary
The ability to take-up DNA from the environment is widely spread among eubacteria, including Gram-positive and Gramnegative species [1]. In Gram-positives, a global transcription factor or sigma factor coordinate the expression of genes required for efficient DNA uptake and recombination, the so-called late competence genes. In Streptococci, the conserved ComX sigma factor activates the late competence genes [5], while the global transcription factor ComK has been identified in various Bacilli to activate gene expression of genes related to DNA uptake [7]. We wanted to test if the product of the comK gene can activate transcription For this we first introduced the comKBco gene (cloned in pATK4) into B. subtilis harboring a PcomGABsu-gfp reporter that enables us to monitor the activation of gene expression. Introduction of comKBco into B. subtilis resulted in low comGABsu expression, which suggests the lack of complete functional complementation of comKBsu deletion under the tested conditions. No natural transformation was observed in the complemented B. subtilis strain (data not shown)
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