Regulation of Arginine Metabolism during Soy Sauce Fermentation Process By Metabolic Engineering of Moromi Microbes

The industrial fermentation for fermented foods or condiments production is a process usually using a complex microflora as the producer. Lactic acid bacteria (LAB) play important roles in food mature processing and aroma components production, whereas the utilization of arginine through the arginine deiminase (ADI) pathway by LAB may cause the accumulation of citrulline, which is the precursor of ethyl carbamate, the group 2A carcinogen.

LAB utilize arginine as the supplement for obtaining energy, and ammonia released with arginine metabolism through the ADI pathway also contributes to their resistance to acidic stress. Generally the end product for ADI pathway is ornithine and not much of citrulline is produced. However, the conversion of citrulline to ornithine may not be sufficient when LAB strains are exposed to stress (i.e. osmotic stress). This is the main reason that citrulline accumulated in the moromi during soy sauce fermentation. Given the fact that genetic modification of microorganisms for food production is not acceptable, also the natural microbiota of the moromi can hardly be constantly genetic modified, metabolic engineering of the ADI pathway is done by strain interference. A Bacillus strain isolated from the moromi was selected for regulation of arginine metabolism during soy sauce fermentation. We successfully increased the efficacy of citrulline decomposition in the moromi with the employment of this Bacillus strain. The result demonstrated a good example in regulation of a substance metabolism without genetic engineering a strain, which might give a better knowledge for engineering microbial metabolism pathways in a complex microflora.