Development of Co-Culture Systems of Lactic Acid Bacteria and Yeasts for Bioproduction

Co-culture systems of lactic acid bacteria and yeasts for bioproduction are described with two typical examples. A novel control method exploiting microbial interaction in the co-culture system is introduced as the first example. In order to control pH in an antimicrobial peptide (nisin) production process by Lactococcus lactis subsp. lactis (ATCC 11454), microbial interaction between L-lactate production by L. lactis and its assimilation by Kluyveromyces marxianus was utilized. A cascade pH controller coupled with DO control was newly developed and the specific lactate consumption rate of K. marxianus was controlled by changing the dissolved oxygen (DO) concentration. pH and lactate were kept at constant levels and nisin accumulated in medium to high levels, compared with other pH control strategies, such as processes without pH control and with pH control by addition of alkali. The second example is polysaccharide kefiran production by co-culture of Lactobacillus kefiranofaciens and Saccharomyces cerevisiae. Productivity of kefiran was increased in the co-culture system of S. cerevisiae under an aerobic condition. Not only the effect of removal of lactic acid but also the additional effect of S. cerevisiae are discussed through the simulation of the system.