Salt requirements in the denitrifying bacterium Pseudomonas nautica 617

Pseudomonas nautica 617, which was isolated from superficial marine sediment, was found to require sodium for growth. Growth also appeared to be sensitive to the divalent cation, Mg2+, the presence of which, together with that of Na+, was necessary for achieving maximal growth. We investigated cell capacity to resist lysis after washing with either 0.05 M MgCl2 or 0.5 M NaCl, by monitoring suspension optical density changes as well as the release of ultraviolet absorbing material. Mg2+ turned out to play a significant role in stabilizing the structure of the cell envelope. Respiratory activity was also sensitive to ionic environment. With cells washed with 0.05 M MgCl2 and suspended in 0.05 M Tris buffer, the respiration rate, assessed by N2O evolution, was 15% of that measured in artificial sea water. Upon addition of 0.5 M Na+, nitrous oxide production rose to 32% of the reference level. The dinitrification rate was fully restored by further addition of 0.05 M Mg2+. K+ alone had almost no effect, but when added with Na+, the rate of denitrification increased to 45%.