Growth of Pseudomonas aeruginosa on nitrous oxide

Three strains of Pseudomonas aeruginosa were grown anaerobically on exogenous N2O in a defined medium under conditions that assured the maintenance of highly anaerobic conditions for periods of 1 week or more. The bacteria were observed reproducibly to increase their cell density by factors of 3 to 9, but not more, depending on the initial amount of N2O. Growth on N2O was cleanly blocked by acetylene. Cell yields, CO2 production, and N2O uptake all increased with initial PN2O at PN2O less than or equal to 0.1 atm. Growth curves were atypical in the sense that growth rates decreased with time. This is the first observation of growth of P. aeruginosa on N2O as the sole oxidant. N2O was shown to be an obligatory, freely diffusible intermediate during growth of strains PAO1 and P1 on nitrate. All three strains used this endogenous N2O efficiently for growth. For strains PAO1 and P1, it was confirmed that exogenous N2O had little effect on the cell yields of cultures growing with nitrate; thus, for these strains exogenous N2O neither directly inhibited growth nor was used significantly for growth. On the other hand, strain P2 grew abundantly on exogenous N2O when small and growth-limiting concentrations of nitrate or nitrate (2 to 10 mM) were included in the medium. The dramatic effect of these N-anions was realized in large part even when the exogenous N2O was introduced immediately after the quantitative conversion of anion-nitrogen to N2. No evidence was found for a factor in filter-sterilized spent medium that stimulated fresh inocula to grow abundantly on N2O.(ABSTRACT TRUNCATED AT 250 WORDS)