The effect of extracellular DNA（eDNA） on bacterial attachment was characterized using Escherichia coli,DNase I,and several different kinds of DNA.Here,we showed that eDNA en-hanced bacterial attachment to solid surface in a concentra-tion-dependent way.Either plasmid DNA or chromosome DNA,even or eukaryotic DNA fragments showed the promotion effect,suggesting that the effect of DNA on bacterial attachment is non-specific.This promotion effect of eDNA is separable from that of conjunctive pili.In a static culture system,biofilm can form even with the presence of active DNase I.DNase I impaired bacte-rium-to-bacterium adhesion and microcolony formation efficiently but had little effect on bacterial attachment to a solid surface and mature biofilm.Consequently,this study provides a rational de-scription for the role of DNA in bacterial biofilm formation in natural environments.
The natural transformation of Escherichia coli is a novel and recently developed system that has significance for genetic studies and the biological safety of genetic engineering.However,the mechanisms of transformation,including development of competence and DNA uptake,are not thoroughly understood.In this study,we demonstrated the effect of the general stress response regulator RpoS,which has been associated with E.coli transformation,on natural transformation performed in an‘‘open system’’.We find that RpoS is required for natural transformation but not to artificial transformation and RpoS mainly affect transformation in the liquid culture prior to plating.In the liquid culture,RpoS over-expression promotes natural transformation in early exponential phase and static incubation accumulates RpoS and promotes transformation to a limited extent.These findings provide detailed understanding of RpoS function on natural transformation.
