Raphidiopsis raciborskii (CYRF-01): Habilidade de secreção de vesículas extracelulares em condições de creshabilidade de secreção de vesículas extracelulares em condições de crescimento normal e em resposta a estímulos ambientais em culturacimento normal e em resposta a estímulos ambientais em cultura

Abstract

Secretion of vesicles at the cell surface, collectively termed extracellular vesicles (EVs), is an important biological process of both eukaryotic and prokaryotic cells associated with functional activities and DNA transfer. This process has been demonstrated in bacteria from aquatic ecosystems, but it is still poorly characterized in cyanobacteria. In the present work, we investigated if Raphidiopsis raciborskii (CYRF-01), a globally distributed cyanobacterium species with increasing presence in freshwater environments, is able to release EVs when exposed to environmental stressors (ultraviolet radiation or co-culture with another cyanobacterium species - Microcystis aeruginosa. Non-axenic cultures of R.raciborskii (CYRF-01) were exposed to ultraviolet radiation (UVA + UVB) for 6 h period, treatment that induces structural damage to this species while co-cultures with MIRF-01 were kept for 24 h. After the incubation times, cell density and viability were analyzed, and samples were processed for transmission electron microscopy (TEM). Our ultrastructural analyses revealed that R.raciborskii constitutively releases EVs from the outer membrane during its normal growth and amplifies such ability in response to environmental stressors. Both situations induced significant formation of outer membrane vesicles (OMVs) by R.raciborskii compared to control cells. Quantitative TEM revealed an increase of 48% (UV) and 60% (interaction) in the OMV numbers. Considering all groups, the OMVs ranged in size from 20 to 300 nm in diameter, with most OMVs showing diameters between 20 and 140 nm. Additionally, molecular analysis of the cellular envelope revealed that formation of OMVs is accompanied by phosphatidylserine exposure, an event also observed in EVsecreting eukaryotic cells. Altogether, we identified for the first time that R.raciborskii has the competence to secrete OMVs and that under different stress situations the genesis of these vesicles is increased. The amplified ability of cyanobacteria to release OMVs may be associated with adaptive responses to changes in environmental conditions and interspecies cell communication.