The interaction between Bacillus megaterium(also called big bacterium)and Ketogulonicigenium vulgare (also called small bacterium)was studied for 2-keto-L-gulonic acid (2-KGA)mixed culture fermentation.The following mechanisms were found.(1)Big bacterium might adjust its growth behavior by quorum sensing.(2)Metabolites and autolysis substances of big bacterium were beneficial to overcoming the metabolic defects of small bacterium and therefore accelerating the latter's growth.(3)Small bacterium released lysozyme to promote big bacterium's autolysis.(4)Big bacterium autolysis released specific protease substances to enhance sorbitol dehydrogenase (SDH)which might increase the synthesis rate of 2-KGA.Based on such mechanisms

a kinetic model of 2-KGA mixed fermentation was established.Model validation was carried out with four sets of experimental data under different cultivation conditions.The results demonstrated that the proposed model was able to well describe the growth of two bacteria and 2-KGA production.