Metal-induced biofilm formation by radiation resistant bacteria Deinococcus radiodurans and Deinococcus indicus.

Biofilms confer structural and functional advantages, playing a crucial role in the survival and resilience of microorganisms in diverse environments. Given its critical importance, most efforts focus on pathogenic bacteria and common bacterial isolates overlooking the natural diversity of extremophilic groups, as the case of highly radiation resistant members of the Deinococcus genus. Here, we investigated the ultrastructural features Deinococcus radiodurans and Deinococcus indicus growing under two commonly used medium formulations TGY and M53 and differentially supplemented with metal ions. Specie-level pleomorphic behavior in Deinococcus spp. was positively correlated to media culture, inducing distinct morphological alterations with multicellular clustering in D. radiodurans under M53, while cell elongation and swelling in D. indicus grown under TGY conditions. Ultrastructure analysis provided information of biofilm structure, in which extracellular polymeric substance (EPS) matrix was only observed in D. radiodurans and enhanced under Mn and Fe supplementation, while D. indicus showed high surface adhesion. Compared to reported biofilms, both species showed abundant membrane vesicles (MVs), providing a rational basis for biofilm cohesion and cell adhesion in this species. Arsenic used as toxic metal condition, did not impact biofilm structure, opening new avenues for potential bioremediation approaches.