Anaerobes Wachstum von Corynebacterium glutamicum durch gemischte Säurefermentation

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Corynebacterium glutamicum can grow anaerobically using nitrate as an electron acceptor, but low cell densities are achieved due to toxic nitrite. While it is metabolically active without oxygen, producing lactate, succinate, and acetate from glucose, its fermentative anaerobic growth had not been previously described. This study investigated C. glutamicum's potential for fermentative growth and amino acid production under anaerobic conditions. Results showed that the wild type could grow anaerobically in minimal medium with glucose, fructose, sucrose, and ribose, achieving optical densities of 1.9 (sucrose), 2.2 (glucose), and 2.7 (fructose and ribose). However, it could not utilize gluconate, pyruvate, lactate, acetate, or propionate. Growth experiments indicated energy limitation as a factor in poor anaerobic growth, and amino acid production (lysine, leucine, valine) was not feasible under tested conditions. The addition of peptides improved anaerobic growth significantly, allowing the cells to conserve energy for essential processes. A mutant lacking acetate formation genes achieved higher cell densities (OD600 = 16.8) and produced 64% less acetate than the wild type. Additionally, the pH tolerance range of C. glutamicum was notably reduced under anaerobic conditions, with slower pH homeostasis observed, as the respiratory chain's efficiency in expelling protons was compromised.