Towards semi-synthetic microbial communities: enhancing soy sauce fermentation properties in B. subtilis co-cultures

Abstract

Background Many fermented foods and beverages are produced through the action of complex microbial communities. Synthetic biology approaches offer the ability to genetically engineer these communities to improve the properties of these fermented foods. Soy sauce is a fermented condiment with a vast global market. Engineering members of the microbial communities responsible for soy sauce fermentation may therefore lead to the development of improved products. One important property is the colour of soy sauce, with recent evidence pointing to a consumer preference for more lightly-coloured soy sauce products for particular dishes. Results Here we show that a bacterial member of the natural soy sauce fermentation microbial community, Bacillus , can be engineered to reduce the ‘browning’ reaction during soy sauce production. We show that two approaches result in ‘de-browning’: engineered consumption of xylose, an important precursor in the browning reaction, and engineered degradation of melanoidins, the major brown pigments in soy sauce. Lastly, we show that these two strategies work synergistically using co-cultures to result in enhanced de-browning. Conclusions Our results demonstrate the potential of using synthetic biology and metabolic engineering methods for fine-tuning the process of soy sauce fermentation and indeed for many other natural food and beverage fermentations for improved products. Electronic supplementary material The online version of this article (10.1186/s12934-019-1149-2) contains supplementary material, which is available to authorized users.

Prevalence, Diversity and UV-Light Inducibility Potential of Prophages in Bacillus subtilis and Their Possible Roles in Host Properties

“…For example, UV-light, an established prophage inducer [ 16 ], is used for sterilization in food industries [ 51 ]. Likewise, some foods such as soy sauce, which are predominantly fermented by B. subtilis [ 52 , 53 ], are reported as being prophage inducers [ 54 ]. Desirable or not, it needs to be experimentally proven whether any of these putative genes play a role in the bacterial property and thus require further studies.…”

Recent progress and advances in soy sauce production technologies: A review

“…The next stage in fermented soy sauce production is an anaerobic salt mash or moromi in Japanese, where the molded soybeans are mixed with 18%-23% NaCl solution, which facilitates lactic acid and yeast fermentation that tolerate the high salt concentration but limits the growth of spoilage microorganisms and pathogens. LAB metabolizes sugars to lactic acid lowering the pH of the moromi gradually from 6.5-7 to 4.0-5.0, and yeast produces alcohol (alcohol fermentation; Det-udom, Gilbert, et al, 2019;Luh, 1995). The moromi is fermented and aged at ambient temperatures over 3 months to 4 years (Yang et al, 2017), with the diverse microorganisms developing various flavor compounds crucial for the final product's organoleptic properties.…”

“…Staphylococcus sp. SSB48 and B. amyloliquefaciens SSB6 were selected based on their potential xylose fermentation capacity, which is related to the Maillard reaction and their significant melanoidin degradation without altering the aromatic complexity in the mature moromi (Det-udom, Gilbert, et al, 2019).…”

“…The interdependence of different microbial species, including bacteria, yeast, and fungi, is complex during soy sauce manufacture because of the non-sterile atmosphere and the long fermentation time, with the microbial activity contributing significantly to the stability and consistency of the final components of soy sauce (Det-udom, Gilbert, et al, 2019;Devanthi & Gkatzionis, 2019).…”

“…The microorganisms in the koji fermentation step, mainly members of the Aspergillus genus (A. oryzae or A. sojae), produce enzymes that breakdown soybean and wheat into simple molecules used for the development of halophilic bacteria including lactic acid bacteria (LAB), Bacillus species, and yeasts during the moromi stage with 18%-20% salt content. The mash is allowed to ferment for 1 month to 4 years of maturation to finally produce soy sauce (Det-udom, Gilbert, et al, 2019;Harada et al, 2017). Apart from fermentation, soy sauce can also be made via chemical hydrolyzation by adding hydrochloric acid to hydrolyze the soybean protein to shorten the production time from several months to 1-3 days.…”