Growth Rate, Biomass Production and Carbon Balance of Pseudomonas aeruginosa at pH Extremes in a Carbon-Limited Medium

Abstract

The aerobic growth of a baderium (Psmdomoms aeruginosa) in a carbon-limited medium was studied from an ecological viewpoint with special reference to the effect of the medium pH.
(1) Ps. aeruginosa was cultured at pH 7.2 in a glucose-limited medium (glucose-C, 300 mg·l^-1; culture temperature, 25°C; osmotic pressure, 2.9 bar). The specific growth rate was 0.44·hr^-1 at the exponential phase. The efficiency of biomass production (biomass-C produced/glucose-C consumed) was 0.48 in the early stage of the stationary phase. The balance of carbon at this stage was as follows; 48% of the glucose-C consumed was produced as biomass-C, 7% was excreted as metabolite-C and 45% was respired as CO₂-C.
(2) Ps, aeruginosa was cultured at pH between 3.5 and 9.7 in the glucose-limited medium. The specific growth rates at pH between 6.2 and 7.6, and the efficiencies of biomass production and the balances of carbon between 5.6 and 8.2 were almost constant, showing the same values as those mentioned above. At pH above or below these ranges, the rate and the efficiency decreased, and the respired CO₂-C increased with some increases in metabolite-C. Biomass production was not observed at pH 3.8 or 9.4, although some glucose consumption was observed.
(3) The constant efficiency of the biomass production at between pH 5.6 and 8.2 suggests that intracellular pH might be maintained by an energy-independent process in this pH range, On the contrary, the decrease in the efficiency above ar below this pH range indicates that intracellular pH might be maintained by an energy-dependent process.
(4) The pH range, in which either constant efficiency of biomass production or specific growth rate at 25°C was observed, decreased when culture temperature decreased (15°C) or increased (37°C). On the contrary, this pH range increased when a mixed substrate was added or a mixed bacterial population was cultured.