Limited use of L-proline as a nitrogen source by Escherichia coli during anaerobic growth

Escherichia coli is a facultative anaerobe that occurs in the gastrointestinal and urinary systems where the pO2 can vary. Strain BW25113 and mutants with deletions of the put A, put P, pro P, and pro W genes were grown in a minimal medium containing 10 mmol L-1 L-proline as the sole nitrogen source. Although good growth occurred under aerobic conditions, growth under anaerobic conditions was poor. All the strains except JW0999 (Δput A::kan) showed faint growth with 0.5% D-glucose in absence of added salt but no growth in the presence of 0.3 mol L-1 NaCl. Strains BW25113, JW4072 (Δpro P::kan), and JW2653 (Δpro W::kan) exhibited faint growth with 0.5% glycerol and 40 mmol L-1 fumarate in the absence of added salt but only BW25113 showed any growth in the presence of 0.3 mol L-1 NaCl. These results indicate that E. coli can utilize L-proline anaerobically but growth is very limited and inhibited by osmotic stress.