Diversity and Ecology of Salt Tolerant Lactic Acid Bacteria : Tetragenococcus halophilus in Soy Sauce Fermentation

Soy Sauce (Shoyu) is one of the most representative Japanese traditional fermented foods and has recently become increasingly popular throughout the world. During the moromi-fermentation of soy sauce making processes, a group of lactic acid cocci known as Tetragenococcus halophilus proliferate in moromi-mash which contains a high concentration of sodium chloride, around 18% (w/v) , and produce nearly 1% (w/v) of L-lactic acid. In the early 1980's, a technique for discriminating individual strains was developed, and as a result the diversity in physiological properties among the natural flora of soy lactic acid bacteria has become well known. A wide variety of strains have been found based on physiological properties such as arginine degradation, aspartate decarboxylation, amine-formation from histidine, phenylalanine or tyrosine, consumption of citric or malic acids, and reduction of environmental red-ox potentials, besides in utilization of carbohydrates. Diversity among strains was also observed in their phage-susceptibility and plasmid-profiles. Many of these activities substantially affect the quality of the end products. Accordingly, strain-level control of the fermenting microbes is needed for preparation of high quality soy sauce. Significance of this diversity and possible mechanisms which might have produced it were also discussed from a microbial ecology perspective.