Corynebacterium efficiens sp. nov., a glutamic-acid-producing species from soil and vegetables

This study describes the identification and characterization of a new bacterial species, Corynebacterium efficiens, isolated from soil and vegetable samples in Japan. Three strains were identified as belonging to the genus Corynebacterium through chemotaxonomic analysis and 16S rRNA gene sequencing. The most distinctive feature of this new species is its ability to grow at 45°C while producing glutamic acid, a characteristic not observed in previously known glutamic-acid-producing corynebacteria. The strains showed 16S rRNA sequence similarity of 95.3% to the closely related C. glutamicum and DNA-DNA hybridization values below 20% with existing species but above 80% among themselves, confirming they represent a genetically distinct species. The bacteria are gram-positive, non-motile rods that ferment various sugars and produce high levels of L-glutamic acid under aerobic conditions. This thermotolerant characteristic has significant industrial potential, as fermentation at higher temperatures could reduce cooling costs in commercial L-glutamic acid (monosodium glutamate) production. The type strain YS-314T is designated as the reference for C. efficiens sp. nov.

Key findings

• Three glutamic-acid-producing bacterial strains isolated from soil and vegetables represent a new Corynebacterium species, designated C. efficiens, distinguished by phylogenetic and DNA-DNA relatedness analyses.
• C. efficiens can grow substantially at 45°C while producing L-glutamic acid, a temperature at which previously known glutamic-acid-producing corynebacteria cannot survive.
• The new species produces acid from dextrin and assimilates L-lactate, characteristics differentiating it from the closely related species C. glutamicum and C. callunae.
• The thermotolerant growth capability of C. efficiens has economic advantages for industrial fermentation by reducing the need for cooling systems in monosodium glutamate production.