Characterization of the spore germination response and UV-C resistance of Bacillus subtilis biofilms

Abstract

In the natural environment, spores and biofilms exhibit remarkable resilience against various environmental stressors, presenting significant challenges to multiple fields, including medicine, industry and space research. Microorganisms incorporated within biofilms possess adhesive properties that enable their attachment to diverse surfaces. The resilience of spores and biofilms contributes to their capacity to induce health complications and posing difficulties to eradication efforts. Spores of Bacillus subtilis are frequently used as bioindicators for sterility due to their high resistance to commonly used decontamination methods such as heat or UV-C radiation. However, upon germination, spores become more vulnerable. This study aims to delve deeper into the germination dynamics of spores within biofilms and investigates the effects of UV-C radiation exposure on both spores and biofilms, specifically of Bacillus subtilis. Moreover, the investigation extends to evaluating how UV-C radiation impacts the subsequent germination ability of spores within biofilms. Particularly, the study examines the impact of exopolysaccharides (EPS) within the extracellular matrix in conferring resistance to UV-C radiation. The findings highlight the critical importance of time and concentration parameters in efficiently inducing spore germination in biofilms. Nonetheless, even upon successful germination, the further development of biofilms presents a persistent challenge. Regarding UV-C radiation, it demonstrates a germicidal effect on spores, particularly evident in the wildtype strain, which exhibit heightened susceptibility compared to the eps mutant. Notably, UV-C radiation shows minimal impact on biofilms and does not significantly influence spore germination post-exposure. It is suspected that EPS are not the sole protective mechanism, as there is no observed reduction in cell viability in the eps mutant strain. Further research approaches could investigate the potential influence of biofilm density on the efficacy of UV-C irradiation and whether the penetration depth of UV-C irradiation may prove insufficient in certain scenarios. In addition, investigating alternative mechanisms that contribute to biofilm resilience could provide valuable insights for the development of more effective eradication strategies.