Effect of micro-nanobubbles with different gas sources on the growth and metabolism of chemoautotrophic microorganisms

Abstract

Micro-nanobubbles (MNBs) have excellent stability and a long retention time in water; their properties vary greatly with different gas sources. In this study, the effects of MNBs with different gas sources, including CO2, N2, O2, and air, on growth and metabolism of the chemoautotrophic strain Sinomicrobium oceani WH-15, which fixes CO2 via the Calvin-Benson-Bassham pathway, were evaluated. MNBs at low concentrations (5–20 %) could promote microbial growth with a maximum increase of 55 % (air MNBs) whereas MNBs at high concentrations (20–50 %) inhibited microbial growth with a maximum decrease of − 79 % (CO2 MNBs). The influence of MNBs was achieved through indirect and direct roles. MNBs with different gas sources had different effects on physical and chemical factors (pH, dissolved oxygen, oxidation-reduction potential, and conductivity) of microbial culture medium. MNBs at high concentration led to an increased intracellular antioxidant capacity of microorganisms and a decrease in the intracellular reduced glutathione, which may be due to exogenous reactive oxygen species produced by MNBs. MNBs could bring reducing power to microorganisms and reduce their metabolic output of extracellular polysaccharides. Our results demonstrated that MNBs with different gas sources improved microbial CO2 fixation through different mechanisms.