Insight into Pseudomonas aeruginosa pyocyanin production under low-shear modeled microgravity

Long-term space flight impairs the immune system of astronauts, rendering them vulnerable to opportunistic infections. Pseudomonas aeruginosa causes opportunistic infections, particularly in individuals with a compromised immune system; it can be a major health hazard for astronauts during space flight missions. Hence, the production of the most abundant redox active virulence factor, pyocyanin by P. aeruginosa, was assessed under low-shear modeled microgravity (LSMMG) conditions, simulated using a high aspect ratio vessel. Moreover, we evaluated changes in the expression of genes involved in pyocyanin biosynthesis and genes involved in the MexGHI-OpmD operon quorum sensing. Extracellular DNA and H₂O₂ production were measured, and their correlation with pyocyanin production was examined. Interestingly, the pyocyanin quantity was 2.58-fold lower in the LSMMG conditions compared to the normal gravity. LSMMG caused downregulation of the genes associated with pyocyanin biosynthesis. Interestingly, extracellular DNA and H₂O₂ release were significantly high in the normal gravity environment. Scanning electron microscopy revealed aggregation and elongated cells under LSMMG. Taken together, these findings suggest that LSMMG did not induce pyocyanin secretion in P. aeruginosa.