The influence of pH value and aeration on the growth of Aerobacter aerogenes and Bacterium coli in defined media.

Abstract

The total amount of growth of Aerobacter aerogenes and Bacterium coli in glucose ammonium salt media which provided substrates in excess was dependent on the initial pH value in aerated and unaerated cultures. Total crops in aerated cultures were always higher for any particular initial pH value, and for cultures inoculated at pH values less than 7·0 the pH fell to lower values in aerated than in unaerated media. Growth of a culture of A. aerogenes in its (unaerated) stationary phase resumed on aeration; when the pH value at inoculation was 5·0–6·0, the pH continued to fall; when the pH value at inoculation was 6·1–7·0, the pH rose slightly. Growth of similar cultures of Bact. coli lagged when aerated; pyruvate concentrations immediately increased and pH values fell when glucose was in excess but not when it was limiting for growth. The concentration of formic acid produced by fully grown cultures was sufficient to abolish growth in fresh media below pH 5·25 but not at pH 7·0. These observations are discussed in relation to views on the influence of aeration on growth. Relationships between total growth and initial pH value of citrate media were established for aerated and unaerated cultures of A. aerogenes. Growth in unaerated media ceased at pH values slightly higher than those at inoculation, leaving some citrate unconsumed. Aeration then caused growth resumption accompanied by consumption of citrate and a further increase in alkalinity.