Produção de vesículas de membrana externa de ecossistemas aquáticos em resposta à radiação ultravioleta e interação com vírus

Abstract

Production of outer membrane vesicles (OMVs), membrane-delimited structures with 20 to 300 nm in diameter, is an important process of secretion of Gramnegative bacteria. This process has been characterized in pathogenic bacteria, in which OMVs are involved in events of bacterial survival, cell signaling, secretion of virulence factors, pathogenesis, nutrient acquisition and biofilms formation, but it is still poorly known in bacteria from aquatic ecosystems. The formation and factors that influence the regulation and production of OMVs under stressful conditions require additional research. The goal of the present work was to investigate, the production of OMVs by Gram-negative bacteria obtained from aquatic ecosystems and cultured (non-axenic cultures) after exposure to ultraviolet radiation (UVR) or interaction with viruses, as environmental stressors. We analyzed cell density, viability and ultrastructure. First, we showed that UVR and virus infection induce bacterial death. Both stressors triggered a significant negative effect on cell density and viability after treatment. This decrease was directly associated with cell death, as corroborated by transmission electron microscopy (TEM) that revealed morphological changes and i viruses in the cytoplasm of degenerating bacteria. Second, detailed qualitative and quantitative ultrastructural analyzes demonstrated that bacteria are constitutively capable of releasing OMVs during their growth and amplify this ability when exposed to UVR or viral infection. Our studies captured the bacterial vesiculation process with clear visualization of the trilaminar structure of the secreted vesicles. Moreover, in parallel to increased vesiculation, we observed reduction in the size of the OMVs. This might be explained by the rapid production of these membranous structures, which may be affecting membrane replenishment and dynamics required for vesicle formation. Our findings recognize, for the first time, the secretory pathway through OMVs as a possible adaptive and protective response of bacteria from aquatic ecosystems to rapid changes in the environmental conditions. This is important to understand aspects from the bacterial community dynamics.