Clarification of interactions among microorganisms and development of co-culture system for production of useful substances.

Co-culture systems containing two microorganisms for the production of useful substances are described. We developed a novel co-culture system composed of two fermentors and two microfiltration modules. The proposed co-culture system allowed regulation of the dissolved oxygen concentration at a level suitable for an individual microorganism in each fermentor, as well as the successful exchange of culture medium between two fermentors. By co-culture, using a combination of Pichia stipitis and Saccharomyces cerevisiae, ethanol was produced efficiently from a mixture of glucose and xylose. Moreover, the useful probiotic cells were simultaneously produced with a high productivity by our co-culture using a combination of Bifidobacterium and Propionibacterium. Kefiran production by Lactobacillus kefiranofaciens alone under the culture conditions, established by mimicking the presence and activities of yeast cells in kefir grains, was also investigated. The results obtained showed that under the culture conditions established by mimicking the actions of yeast cells on L. kefiranofaciens in kefir grains, the amount of kefiran produced was enhanced, even when the lactic acid bacterium alone was used.