Microbial respiratory quinones as indicator of ecophysiological redox conditions

The bacterial respiratory quinones and membrane phospholipid fatty acids (PLFA) were measured to test the biochemical responses to the redox conditions after the respiration of diverse electron acceptors by microorganisms. Shewanella putrefaciens strain CN32 was examined for its growth with O₂, nitrate, ferrihydrite, ferric citrate, and sulfite as electron acceptors. The same parameters were also measured for Desulfovibrio desulfuricans strain G-20, Geobacter metallireducens strain GS-15, Thioploca spp., two strains of magnetotactic bacteria (Magneteospirilum magnetotactium marine vibrioid strain MV-1 and M. sp. strain AMB-1), and environmental sediments. Microorganisms with aerobic respiratory of oxygen (MV-1 and AMB-1) have high ratios of monounsaturated to saturated straight chain PLFA and ubiquinone to menaquinone ratios; while those that conduct strict anaerobic respirations (G-20 with sulfate and GS-15 with ferric iron) have low ratios of monounsaturated to saturated straight chain PLFA and uniquinone to menaquinone ratios. The facultative respiratory of nitrate (Thioploca) has these parameters in the middle. The ratios of menaquinones to ubiquinones in CN32 cells systematically increase according to the increase of redox potential and bioavalibility of electron acceptors. The correlation between σUQ-n/σMK-n ratios and redox conditions indicates the structure of respiratory quinone responses sensitively to the microbial ecophysiological conditions.