Microcystis enhanced production of extracellular superoxide radicals by Pseudomonas and its mechanism
The production of biogenic superoxide radical,a critical group of reactive oxygen species in natural waters,was explored in this study by examining interspecies electron transfer involving M.aeruginosa and Pseudomonas,both prevalent in aquatic environments.The results showed that algal presence significantly augmented the generation of extracellular superoxide radical by Pseudomonas,a process notably influenced by diurnal light cycles.Crucially,this enhancement was not attributable to variations in microbial densities or background constituents of the water bodies;rather,it stemmed from substance exchanges between the bacteria and algae.Furthermore,as the incubation period extended,an increase in extracellular superoxide radical production was correlated with a reduction in bacterial density.This trend was likely due to elevated external oxidative stress from the abundant superoxide radicals,leading to morphological changes such as surface crumpling and subsequent cellular decay in the bacteria.To elucidate the mechanisms behind the enhanced generation of superoxide radicals by M.aeruginosa-stimulated Pseudomonas,the roles of reducing coenzymes Ⅰ(NADH)and Ⅱ(NADPH)were analyzed,which were intimately linked to the generation of these radicals.This finding revealed a significant uptick in NAD(P)H levels within the bacterial-algal coexistence system concurrent with the increase in superoxide radical production.This suggested that NAD(P)H generated by the algae via photosynthesis can be exocytosed into the extracellular environment,thereby influencing bacterial electron transfer and facilitating superoxide radical production.Additionally,the elevation in NAD(P)H levels also appeared to impair the bacterial antioxidant system,diminishing the bacterial capacity to scavenge superoxide radicals,thus fostering their accumulation.These insights unveiled a novel aspect of bacterial-algal interactions and were pivotal for comprehending the microecological dynamics in natural waters,with implications for environmental pollutant degradation and ecological balance.
bacteria and algae coexistence systemextracellular superoxide radicalMicrocystis aeruginosaPseudomonas
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