[Selection of bacterial strains for the production of threonine]

The production of L-threonine in submerged culture was studied in the following bacterial strains; Brevibacterium flavum ATCC 21269, Corynebacterium acetoacidophilum ATCC 21270, Escherichia coli ATCC 21149, E. coli NRRL 12098, E. coli NRRL 12099 and E. coli NRRL 12100. Erlenmeyer flasks with different volumetric relations liquid/recipient, were used to study the influence of the volumetric oxygen transfer rate. B. flavum reached levels of threonine of 0.72 g/l at 96 hours of culture with a volumetric relation liquid/recipient of 1:5. With a relation 1:25 the maximal level was reached at 48 hours (0.60 g/l of threonine) (Table 1). In addition to threonine this strain accumulated in the culture media glutamic acid (+/- 2 g/l), alanine or glycine and proline. With E. coli ATCC 21149 the aeration favored the production of threonine reaching levels of 0.38 g/l in six day cultures with valine and alanine at levels approximate to 2 g/l. Excepting C. acetoacidophilum, all the strains produced threonine at levels of 0.30 to 3.55 g/l (Table 5). E. coli NRRL 12098 and E. coli NRRL 12100 produced only threonine, the culture medium being free from other aminoacids. With E. coli NRRL 12098 levels of 2 g/l were attained but the production was restricted to the presence of yeast extract in the media (Table 2). E. coli NRRL 12100 was the best strain and the inoculum media influenced the production (Table 3) and the best threonine levels were reached in the best aeration conditions assayed (Table 4) with 3.55 g/l for volumetric relations 1:10 and 1.25 g/l for 1:5.