Major differences between glutamate-fermenting species isolated from chemostat enrichments at different dilution rates

Abstract

From chemostat enrichments conducted at dilution rates of 0.025, 0.12 and 0.25 h−1 glutamate- and aspartate-fermenting bacteria were isolated. The dominant aspartate-fermenting strains in all these enrichments belonged to the genus Campylobacter, whereas 3 dissimilar types of glutamate-fermenting bacteria predominated at the different dilution rates. One of these strains was identified as Clostridium cochlearium. The remaining two were designated as strain DKglu16 (glutamate → acetate + propionate + ammonium + carbon dioxide) and DKglu21 (glutamate → acetate + formate + ammonium + carbon dioxide). Grown in continuous culture under glutamate limitation, strain DKglu16 (μmax= 0.13 h−1; Ks= 1.9 μM) outcompeted C. cochlearium(μmax= 0.36 h−1; Ks= 7 μM) at low dilution rates, but was outgrown at higher rates of dilution (0.044 h−1). In glutamate-limited continuous culture the competitiveness of strain DKglu16 increased considerably when lactate was added to the feed in addition to glutamate.