PROLINE EXCRETION BY ESCHERICHIA-COLI-K12

Proline excretion from proline overproducing strains of E. coli K12 was studied as a model chemical production system. Proline overproducing mutants of E. coli were isolated and it was shown that uncontrolled synthesis is not sufficient to cause excretion of this amino acid. An episomal mutation causing proline overproduction was introduced into a series of isogenic strains with well-defined, chromosomal lesions affecting the active uptake and catabolism of L-proline. A syntropism test revealed that L-proline was excreted by overproducing strains only if transport and/or catabolism were impaired. Dansyl derivatization and chromatographic analysis of culture supernatants showed that proline was the only amino acid excreted. Batch cultures of an excreting strain in an amino acid production medium yielded culture supernatants containing 1 g proline /l. No proline was detectable in supernatants derived from cultures of an overproducing strain with normal transport and catabolic activities. Apparently, genetic lesions eliminating active uptake can be used to specifically enhance metabolite excretion.