Improvement of vitamin B-12 fermentation by reducing the inhibitory metabolites by cell recycle system and a mixed culture

The major problem in vitamin B-12 production using Propionibacterium is the growth inhibition of the cell due to the accumulation of inhibitory metabo lites such as propionic acid and acetic acid. In the present paper, we cons idered several approaches of controlling the propionic acid concentration a t low level. Namely: (1) the periodic cultivation of Propionibacterium wher e dissolved oxygen (DO) concentration was alternatively changed between 0 a nd 1 ppm; (2) cell recycle system using hollow fiber module; and (3) mixed culture using Propionibacterium and Ralstonia eutropha where the latter mic roorganism assimilates the propionic acid produced by the former. It was fo und that the productivity of vitamin B-12 was the highest for the cell recy cle system, while if the performance was evaluated based on the amount of v itamin B-12 produced per medium used, the mixed culture system gave the far highest value. (C) 2000 Elsevier Science S.A. All rights reserved.