Adaptability of a Caproate-Producing Bacterium Contributes to Its Dominance in an Anaerobic Fermentation System

Abstract

The transformation of diverse feedstocks into medium-chain fatty acids (MCFAs) by mixed cultures is a promising biorefinery route because of the high value of MCFAs. A particular concern is how to maintain the microbial consortia in mixed cultures to achieve stable MCFA production. Chinese strong aroma-type liquor ( Baijiu ) fermentation system continually produces caproic acid for decades through a spontaneous inoculation of anaerobes from pit mud into fermented grains. Therefore, illuminating the dominant caproate-producing bacterium (CPB) in pit mud and how the CPB sustains in the spontaneous fermentation system will benefit to reveal the microbiological mechanisms of the stable caproate production. Here, we examined pit mud samples across four Chinese strong aroma-type Baijiu producing areas and found that a caproate-producing Caproicibacterium sp. was widely distributed in these distilleries with relative abundance ranging from 1.4% to 35.5% and an average abundance of 11.4%. Through controlling carbon source availability, we achieved different simplified caproate-producing consortia and found that the growth advantage of Caproicibacterium sp. was highly dependent on glucose. Then two strains, named Caproicibacterium sp. LBM19010 and Caproicibacterium sp. JNU-WLY1368, were isolated from pit mud of two regions. The metabolic versatility of this bacterium utilizing starch, maltose, glucose and lactate reflected its adaptability to the fermentation environment where these carbon sources coexist. The simultaneous utilization of glucose and lactate contributed to the balance between cell growth and pH homeostasis. This study reveals that multiple adaptation strategies employed by the predominant CPB promotes its stability and dominance in a saccharide- and lactate-rich anaerobic habitat. IMPORTANCE Chinese strong aroma-type liquor ( Baijiu ) fermentation environment is a typical medium-chain fatty acid producing system with complex nutrients. Although several studies have revealed the correlation between microbial community composition and abiotic factors, the adaptation mechanisms of dominant species to abiotic environment are still unknown in this special anaerobic habitat. This study identified the predominant CPB in Chinese strong aroma-type Baijiu fermentation system. Metabolic versatility and flexibility of the dominant CPB with a small-size genome indicated that this bacterium can effectively exploit available carbon and nitrogen sources, which could be a key factor to promote its ecological success in a multi-species environment. The understanding of growth and metabolic features of CPB responsible for its dominance in microbial community will not only contribute to the improvement of Chinese strong aroma-type Baijiu production but also expand its potential industrial applications in caproate production.

Caproicibacterium lactatifermentans sp. nov., isolated from pit clay used for the production of Chinese strong aroma-type liquor

“…Strains LBM19010 T and JNU-WLY1368 were isolated from pit clay collected from aged pits of two well-known Chinese strong aroma-type liquor distilleries located in the Anhui Province of China (33° 85′ N, 115° 78′ E) and the Sichuan Province of China (28° 77′ N, 104° 62′ E), respectively. Modified Clostridia growth medium (mCGM) was used to enrich and isolate pure strains and the detailed methods for strain isolation are described in our recent publication [9]. The reference strain Caproicibacterium amylolyticum LBM18003 T was obtained from our laboratory and Caproiciproducens galactitolivorans JCM 30532 T was purchased from the Japan Collection of Microorganisms (JCM).…”

“…LBM19010' and 'Caproicibacterium sp. JNU-WLY1368' were assigned to the family Oscillospiraceae [3][4][5][6][7][8][9]. Caproicibacterium amylolyticum, a caproate-producing bacterium isolated from pit clay of Chinese strong aroma-type liquor fermentation system, was recently proposed to the novel genus Caproicibacterium, belonging to the family Oscillospiraceae in the class Clostridia.…”

“…LBM19010’ and ‘ Caproicibacterium sp. JNU-WLY1368’ [9], the dominant caproate-producing bacterium in pit clay, are still uncertain.…”

Isolation, identification, and whole-genome sequencing of high-yield protease bacteria from Daqu of ZhangGong Laojiu

“…Proteases are a class of enzymes that catalyze the hydrolysis of proteins into peptides and amino acids and degrade proteins into raw materials to form small peptides or amino acids used in yeast and lactic acid bacteria fermentation as a nitrogen source to promote the growth of brewing microorganisms [ 37 ]. Some of the amino acids in the protein degradation products are flavoring substances themselves, while others are precursors of aroma components that ultimately affect the formation and quality of the flavor of white wine [ 38 ]; and thus are indispensable enzymes for white wine production.…”

Nitrogenous compounds and Chinese baijiu: a review

“…The fermentation of Strong flavour baijiu can be divided into eight steps: 1) sorghum broken; 2) moistening sorghum flour; 3) blending moistened sorghum flour, bran shell with the previous round of muzao; 4) distillation; 5) spreading; 6) cellar fermentation; 7) collecting zaopei; Clostridium, Sedimentibacter, Bacteroides, Porphyromonas (40) and Caproicibacterium sp. (80). These microorganisms contribute to the formation of caproic acid.…”