Lactic acid bacteria (LAB) is a collective term for bacteria capable of producing lactic acid from fermentable carbohydrates. Despite their widespread presence in the gastrointestinal tracts of humans and animals, where they play important physiological roles, functional analysis of specific strains from particular sources requires further enrichment. The objective of this study was to explore the differences between Pediococcus acidilactici OM681363 and Lacticaseibacillus paracasei ON606241, both isolated from the rumen of Chinese Holstein dairy cows, using whole-genome sequencing. The results indicate that P. acidilactici OM681363 contained three CRISPR fragments and numerous enzymes involved in carbohydrate degradation. Additionally, P. acidilactici OM681363 possessed more genes related to fiber degradation, especially cellobiose, and the sole carbon source experiment also confirmed this. However, it lacked genes associated with polysaccharide lyase. In contrast, L. paracasei ON606241 was found to be more specialized in breaking down non-fiber carbohydrates, producing more acetic and lactic acids. Overall, P. acidilactici OM681363 may have a greater capacity to degrade complex carbohydrates, while L. paracasei ON606241 appears to specifically target non-fiber carbohydrates.

Rumen bacteria have the ability to efficiently degrade and acidify lignocellulosic biomass, among which rumen solid-phase bacteria are more dominant. However, the effectiveness of in vitro cultured ruminal solid-phase bacteria in producing volatile fatty acids (VFA) during lignocellulosic biomass degradation remains unclear. This study presents a feasibility analysis of the long-term subculture of rumen solid-phase bacteria in vitro for VFA production. The results indicated that VFA production could reach 0.20–0.30 g/g dry matter. After 40 generations (200 days) of subculturing, the bacterial community underwent alterations. The relative abundance of certain fiber-degrading, acid-producing bacteria, which were less abundant in rumen solids, such as Oribacterium and Victivallis, was significantly upregulated following subculturing in vitro. The success of this study in subculturing rumen solid-phase bacteria in vitro over an extended period and achieving efficient VFA production is of considerable importance for the practical application of rumen microorganisms in production settings.

In this study, to enhance the concentration of caproic acid generated from maize straw fermentation and clarify the structures of bacterial and fungal communities within the successively domesticated rumen microbial fermentation system, maize straw was used as the substrate. In a continuous subculture system, the impacts of ethanol addition on pH and gas production were explored, with a focus on the caproic acid yield in the final (eighth generation) generation and alterations in bacterial and fungal communities. Results demonstrated that ethanol could boost the caproic acid concentration in maize straw fermentation by rumen fluid to 1,492 mg/L. Analysis of the microbial community structure indicated that unidentified_Clostridiales, Shuttleworthia, and Syntrophococcus were crucial in ethanol-driven caproic acid production. These findings are highly significant for the high - value utilization of maize straw waste to produce caproic acid via the carboxylic acid platform using rumen microorganisms in industrial processing.

In this study, to enhance the concentration of caproic acid generated from maize straw fermentation and clarify the structures of bacterial and fungal communities within the serially subcultured rumen microbial fermentation system, maize straw was used as the substrate. In a continuous subculture system, the impacts of ethanol addition on pH and gas production were explored, with a focus on the caproic acid yield in the final (eighth generation) generation and alterations in bacterial and fungal communities. The results showed that the relative abundances of unidentified_Clostridiales, Shuttleworthia, and Syntrophococcus in ethanol-driven caproic acid production were enriched by 5.36-fold, 2.61-fold, and 2.25-fold, respectively. This consequently increased the concentration of caproic acid in the fermentation broth to 1492 mg/L, representing a 3.7-fold increase. These findings are highly significant for the high-value utilization of maize straw waste to produce caproic acid via the carboxylic acid platform using rumen microorganisms in industrial processing.