Fermentation characteristics of unsterilized feedstock with a simplified caproate-producing microbial consortium

Abstract:

[Objective] To obtain a stable microbial consortium with a high yield of caproate and achieve high-value carbon recovery from Baijiu-making wastewater (Huangshui). [Methods] We used the plate screening approach to obtain a simplified caproate-producing microbial consortium, evaluated the preferred carbon source of the consortium, and optimized the substrate concentration, pH, and feeding strategy. The metagenomics based on nanopore sequencing was employed to determine the composition and stability characteristics of the simplified caproate-producing microbial consortium. [Results] SimpCom1, a simplified caproate-producing microbial consortium, demonstrated significantly higher conversion rate of lactate than glucose to caproate. When SimpCom1 was used to ferment unsterilized Huangshui, we controlled the working concentration of Huangshui between 30% and 50% and initial pH 5.50 to achieve stable growth and metabolism of the consortium for caproate production. The fermentation was carried out in a fed-batch manner with 50% Huangshui, initial pH 5.50, and pH 6.50-7.00 after 48 h. Within four fed-batch fermentation cycles, the average caproate titer, productivity, proportion of caproate in total acids, and conversion rate of lactate to caproate reached 16.83 g/L, 3.05 g/(L·d), 67.27%, and 0.42 g/g, respectively. The metagenomic analysis showed that Caproicibacterium lactatifermentans, Ligilactobacillus acidipiscis, Clostridium tyrobutyricum, and ‘Butyriproducens baijiuensis BJN0003’ were the core species of SimpCom1. C. lactatifermentans and ‘B. baijiuensis BJN0003’ remained stable growth and metabolism in the unsterilized Huangshui, with the relative abundance of 45.3% and 6.7%, respectively, at the end of fermentation with 50%-diluted Huangshui. [Conclusion] We successfully established an efficient and low-cost approach for producing caproate by fermentation of unsterilized Baijiu-making wastewater with a simplified microbial consortium containing C. lactatifermentans and ‘B. baijiuensis BJN0003’.