The first recorded incidence of Deinococcus radiodurans R1 biofilm formation and its implications in heavy metals bioremediation

Radiation tolerant Deinococcus radiodurans R1 is reported to be a potential bacterium for the treatment of low level active wastes. So far there are no reports on the biofilm producing capability of D. radiodurans and heavy metal biosorption. In this study, it was observed that a recombinant D. radiodurans strain with a plasmid harbouring gfp and kan R has formed significant biofilm (~10 μm thick). Analysis of biofilm matrix components produced by D. radiodurans showed that the matrix consisted primarily of proteins and carbohydrates with a little amount of extracellular DNA (eDNA). Further, studies showed that D. radiodurans biofilm formation was enhanced at higher concentrations (up to 25 mM) of Ca 2+ . Further studies on D. radiodurans biofilm showed that Ca 2+ enhanced significant biosorption of the heavy metals (Co, Ni). In the presence of 25 mM Ca 2+ , the D. radiodurans (Kan r ) biofilm showed 35% and 25% removal of Co 2+ and Ni 2+ respectively. While in the absence of Ca 2+ , D. radiodurans biofilm showed relatively low biosorption of Co (7%) and Ni (3%). Ca 2+ also significantly enhanced exopolysaccharide (EPS) production in the biofilm matrix. This infers that EPS could have mediated the heavy metal biosorption. This study signifies the potential use of D. radiodurans biofilm in the remediation of radioactive waste components. Significance and Impact of this Study This is the first ever recorded study on the Deinococcus radiodurans R1 biofilm. This organism, being the most radioresistant micro-organism ever known, has always been speculated as a potential bacterium to develop a bioremediation process for radioactive heavy metal contaminants. However, the lack of biofilm forming capability proved to be a bottleneck in developing such technology. This study records the first incidence of biofilm formation in a recombinant D. radiodurans , serendipitously, and also discusses its implications in removal of heavy-metals, such as Co and Ni.