Excellent L-proline producers were screened for among sulfaguanidine resistant mutants derived from three typical L-glutamic acid-producing bacteria: Brevibacterium flavum, B. lactofermentum, and C. glutamicum.
The best strain, No. 199, is a sulfaguanidine resistant mutant derived from an isoleucine auxotroph of B. flavum 2247 by nitrosoguanidine. Strain No. 199 produced 35 mg/ml of L-proline after 72 hr of cultivation with 10% glucose as a carbon source. The strain also accumulated purine bases such as adenine, guanine, and hypoxanthine, i.e., degradation products of purine nucleotides. In the mutant, 1.6-2.0 fold more intracellular ATP was found than that in the parent strain; it is a substrate of glutamate kinase relating to L-proline biosynthesis.
On the contrary, the levels of intracellular glutamic acid, a substrate of glutamate kinase, were similar among these strains.
It was confirmed that the increment of internal ATP, which was important in the L-proline production mechanism, was very effective in the improvement of L-proline producers.

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