Steam explosion enhancing Bacillus subtilis fermentation on lignocellulosic biomass to prepare high-titer microecological agents

Steam-exploded lignocellulosic biomass (i.e., wheat bran and soybean meal) was fermented at 37°C for 72 h with Bacillus subtilis (inoculated with the B. subtilis seed solution at a dosage of 0.4 mL/g dry medium) to improve the titer of microecological agents (BSMAs). Results showed that SE-172 group (steam explosion pretreatment at 172°C for 2 min) released bioaccessible nutrients by increasing the reducing sugar and water-soluble protein content to 42.07 ± 0.23 and 5.62 ± 0.21 mg/g solid medium, respectively, which were 71.0 % and 26.4 % higher than those in the raw material. SE-172 also enlarged the specific surface area of lignocellulosic substrates by 1.5 times. Therefore, SE pretreatment modifies physico-chemical properties of lignocellulosic biomass and favors microbial growth during solid-state fermentation (SSF). The viable cell and spore number of SE-172 group reached 2.41 × 10 10 and 2.35 × 10 10 CFU/g dry medium, respectively, which were 2.63 and 2.91 times larger than those of the conventional thermal sterilization group (121°C for 20 min). Dietary supplementation with steam explosion based-BSMAs (SE-BSMAs) improved mice growth, increased digestive enzyme activities, and regulated inflammatory cytokines and short-chain fatty acids (SCFAs) production. The relative abundance of beneficial bacteria, including Firmicutes, Lactobacillaceae , Lachnospiraceae , Rikenellaceae , Pediococcus pentosaceus , and Enterococcus faecalis , increased in the SE-172 group. Therefore, SE-BSMAs showed enhanced synbiotic benefits in regulating inflammatory cytokine production and modulating gut microbiota composition, which presents a promising way to improve industrial production efficiency of BSMAs and value-added utilization of lignocellulosic biomass. • SE releases bioaccessible nutrients and enlarges specific surface area of lignocellulosic biomass. • Physico-chemical properties modification of SSF medium by SE favors microbial growth. • SE-BSMAs regulates inflammatory cytokines and SCFAs production in mice. • SE-BSMAs improves mice’s metabolic function, e.g., carbohydrate metabolism. • SE-BSMAs enriches healthy gut microbiota and enhances immune system of mice.