Competence induction and transformation-negative mutants in aeromonas



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Members of the genus Aeromonas can be isolated from many environmental niches where bacteria exist, but are ubiquitously found in aquatic environments and can be isolated from rivers, lakes, ponds, estuaries, and groundwater. The presence of Aeromonas in water systems, especially in drinking water, is an issue of concern in public health. One reason that members of genus Aeromonas are a threat to human health is their ability to multiply in drinking water, and this adaptation may be due to their ability to undergo transformation. Transformation is one method of bacterial gene transfer, in which extracellular (“naked”) DNA is taken up from the environment, and it is entirely dependent on the competence of the recipient cell. Competence is the physiological state that the cell must enter before it can take up extracellular DNA. Competence in Aeromonas can be induced under laboratory conditions. The nutrient strength and the content of culture media can affect competence induction in Aeromonas. Competence induction is higher in media which have lower nutrient concentrations than in full-strength media. Several factors, such as the pH of the medium and molecules secreted by a growing culture, putative quorum-sensing molecules, can also have an effect on competence induction in Aeromonas. This research found that, the competence of Aeromonas was highest in the range of pH 6 to pH 8. Media with a pH below 6 or above 9 produce reduced or low numbers of transformants. The putative quorum-sensing molecules negatively affected competence induction in Aeromonas. Four putative transformation-deficient strains were isolated by random insertion mutagenesis of strain C-70 and tested for their ability to transform using qualitative and quantitative transformation assays. There were none or greatly reduced numbers of transformants in all the four strains.