Dataset Information

Daqu Fermentation Selects for Heat-Resistant Enterobacteriaceae and Bacilli.

ABSTRACT: Daqu is a spontaneous solid-state cereal fermentation used as saccharification and starter culture in Chinese vinegar and liquor production. The evolution of microbiota in this spontaneous fermentation is controlled by the temperature profile, which reaches temperatures from 50 to 65°C for several days. Despite these high temperatures, mesophilic Enterobacteriaceae (including Cronobacter) and bacilli are present throughout Daqu fermentation. This study aimed to determine whether Daqu spontaneous solid-state fermentation selects for heat-resistant variants of these organisms. Heat resistance in Enterobacteriaceae is mediated by the locus of heat resistance (LHR). One LHR-positive strain of Kosakonia cowanii was identified in Daqu, and it exhibited higher heat resistance than the LHR-negative K. cowanii isolated from malted oats. Heat resistance in Bacillus endospores is mediated by the spoVA 2mob operon. Out of 10 Daqu isolates of the species Bacillus licheniformis, Brevibacillus parabrevis, Bacillus subtilis, Bacillus amyloliquefaciens, and Bacillus velezensis, 5 did not contain spoVA 2mob, 3 contained one copy, and 2 contained two copies. The presence and copy number of the spoVA 2mob operon increased the resistance of spores to treatment with 110°C. To confirm the selection of LHR- and spoVA 2mob-positive strains during Daqu fermentation, the copy numbers of these genetic elements in Daqu samples were quantified by quantitative PCR (qPCR). The abundance of LHR and the spoVA 2mob operon in community DNA relative to that of total bacterial 16S rRNA genes increased 3-fold and 5-fold, respectively, during processing. In conclusion, culture-dependent and culture-independent analyses suggest that Daqu fermentation selects for heat-resistant Enterobacteriaceae and bacilli.IMPORTANCE Daqu fermentations select for mobile genetic elements conferring heat resistance in Enterobacteriaceae and bacilli. The locus of heat resistance (LHR), a genomic island conferring heat resistance in Enterobacteriaceae, and the spoVA 2mob operon, conferring heat resistance on bacterial endospores, were enriched 3- to 5-fold during Daqu fermentation and maturation. It is therefore remarkable that the LHR and the spoVA 2mob operon are accumulated in the same food fermentation. The presence of heat-resistant Kosakonia spp. and Bacillus spp. in Daqu is not of concern for food safety; however, both genomic islands are mobile and transferable to pathogenic bacteria or toxin-producing bacteria by horizontal gene transfer. The identification of the LHR and the spoVA 2mob operon as indicators of fitness of Enterobacteriaceae and bacilli in Daqu fermentation provides insights into environmental sources of heat-resistant organisms that may contaminate the food supply.

SUBMITTER: Wang Z

PROVIDER: S-EPMC6193390 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Daqu Fermentation Selects for Heat-Resistant Enterobacteriaceae and Bacilli.

Wang Zhiying Z Li Pan P Luo Lixin L Simpson David J DJ Gänzle Michael G MG

Applied and environmental microbiology 20181017 21

Daqu is a spontaneous solid-state cereal fermentation used as saccharification and starter culture in Chinese vinegar and liquor production. The evolution of microbiota in this spontaneous fermentation is controlled by the temperature profile, which reaches temperatures from 50 to 65°C for several days. Despite these high temperatures, mesophilic <i>Enterobacteriaceae</i> (including <i>Cronobacter</i>) and bacilli are present throughout Daqu fermentation. This study aimed to determine whether Da ...[more]

PMID: 30120119

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Project description:"Daqu" is a saccharifying and fermenting agent commonly used in the traditional solid-state fermentation industry (e.g., baijiu and vinegar). The patterns of microbial community succession and flavor formation are highly similar among batches, yet the mechanisms promoting temporal succession in the Daqu microbial ecology remain unclear. Here, we first correlated temporal profiles of microbial community succession with environmental variables (temperature, moisture, and titratable acidity) in medium temperature Daqu (MT-Daqu) throughout fermentation. Temperature dynamics significantly correlated (P < 0.05) with the quick succession of MT-Daqu microbiota in the first 12 d of fermentation, while the community structure was relatively stable after 12 d. Then, we explored the effect of temperature on the MT-Daqu community assembly. In the first 4 d of fermentation, the rapid propagation of most bacterial taxa and several fungal taxa, including Candida, Wickerhamomyces, and unclassified Dipodascaceae and Saccharomycetales species, significantly increased MT-Daqu temperature to 55°C. Subsequently, sustained bio-heat generated by microbial metabolism (53 to 56°C) within MT-Daqu inhibited the growth of most microbes from day 4 to day 12, while thermotolerant taxa, including Bacillus, unclassified Streptophyta, Weissella, Thermoactinomyces, Thermoascus, and Thermomyces survived or kept on growing. Furthermore, temperature as a major driving force on the shaping of MT-Daqu microbiota was validated. Lowering the fermentation temperature by placing the MT-Daqu in a 37°C incubator resulted in decreased relative abundances of thermotolerant taxa, including Bacillus, Thermoactinomyces, and Thermoascus, in the MT-Daqu microbiota. This study revealed that bio-heat functioned as a primary endogenous driver promoting the formation of functional MT-Daqu microbiota.IMPORTANCE Humans have mastered the Daqu preparation technique of cultivating functional microbiota on starchy grains over thousands of years, and it is well known that the metabolic activity of these microbes is key to the flavor production of Chinese baijiu. The pattern of microbial community succession and flavor formation remains highly similar between batches, yet mechanistic insight into these patterns and into microbial population fidelity to specific environmental conditions remains unclear. Our study revealed that bio-heat was generated within Daqu bricks in the first 4 d of fermentation, concomitant with rapid microbial propagation and metabolism. The sustained bio-heat may then function as a major endogenous driving force promoting the formation of the MT-Daqu microbiota from day 4 to day 12. The bio-heat-driven growth of thermotolerant microorganisms might contribute to the formation of flavor metabolites. This study provides useful information for the temperature-based modulation of microbiota function during the fermentation of Daqu.

Dataset Information

Daqu Fermentation Selects for Heat-Resistant Enterobacteriaceae and Bacilli.

Publications

Daqu Fermentation Selects for Heat-Resistant Enterobacteriaceae and Bacilli.

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