Involvement of DNA in biofilm formation: features and mechanism of DNA adsorption to bacterial surfaces

Adsorption of DNA to bacterial surfaces plays a crucial role in biofilm formation, genetic transformation and bacterial survival in environments. The relevant features were determined performing adsorption isotherms of DNA to E. coli cells. The results suggest that DNA adsorbing to E. coli is in a source-nonspecific way; a same concentration of long linear DNA is easier to be adsorbed than short linear DNA; DNA adsorption is also influenced by bacterial growth phases and environmental conditions (e.g. temperature, salt type and concentration). To better understand the features of DNA adsorption to bacterial surfaces, the zeta potential of the bacteria was determined. The combined results from the adsorption isotherms and the measurement of zeta potential suggest the inhibition effect of the negative surface potential of E. coli on DNA adsorption. It implies further that the adsorption of DNA to bacterial surfaces is governed by not only DNA receptors but also the negatively charged components of bacterial outer membrane. A mathematical derivation of the experimental data suggests that the electrostatic self-repulsion of DNA may facilitate itself to overcome the electrostatic barrier near the bacterial surfaces to be adsorbed, but this effect is dependent on DNA length and concentration. Moreover, salt ions (e.g. NaCl and MgCl 2 ) can increase the adsorption to bacterial surfaces of DNA via screening the electrostatic potential near the negatively charged surfaces. These results provide important implications for understanding adsorption to bacteria of DNA in natural environments and the relevant bacterial behaviors.