Unbalanced Growth Death Due to Depletion of Mn2+ in Brevibacterium ammoniagenes

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In the microbial conversion of added hypoxanthine to 5′-inosinic acid, Mn2+ concentration in the growth medium is known to have a profound effect both on the yield of 5′-inosinic acid and the morphology of cells of Brevibacterium ammoniagenes. To elucidate the mechanism in which Mn2+ was concerned with cell morphology and 5′-inosinic acid production, effects of Mn2+ on the macromolecular synthesis were measured. It was found that Mn2+ strongly governed deoxyribonucleic acid (DNA) synthesis and that, in the medium lacking Mn2+, DNA synthesis was stopped at the level corresponding to one-fourth to one-third that in the medium supplemented with Mn2+ (100 μg/liter). On the other hand, cellular ribonucleic acid and protein synthesis was quite indifferent to Mn2+ concentration. Consequently, cells showed so-called “unbalanced growth death” after 10 hr of culture, losing the ability to form colonies while cell mass was increasing. The elongated cells turned into irregular forms (bulbous, club-shaped, etc.) which finally lysed. Two main reaction components in the conversion of hypoxanthine to 5′-inosinic acid, phosphoribosylpyrophosphate and hypoxanthine phosphoribosyltransferase, were liberated into the medium during lysis. The role of Mn2+ in the synthesis of DNA and the role of the unbalanced growth death in the conversion of hypoxanthine to 5′-inosinic acid are discussed.

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