AUTHOR=Liu Mengyu , Wang Tong , Wang Lu , Xiao Hanjie , Li Jinhui , Duan Chunhui , Gao Lijie , Liu Yueqin , Yan Hui , Zhang Yingjie , Ji Shoukun 

TITLE=Core microbiota for nutrient digestion remained and ammonia utilization increased after continuous batch culture of rumen microbiota in vitro

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1331977

DOI=10.3389/fmicb.2024.1331977

ISSN=1664-302X

ABSTRACT=<sec id="sec1"><title>Introduction</title><p>This study aimed to investigate the digestive function, urea utilization ability, and bacterial composition changes in rumen microbiota under high urea (5% urea in diet) over 23 days of continuous batch culture <italic>in vitro</italic>.</p></sec><sec id="sec2"><title>Methods</title><p>The gas production, dry matter digestibility, and bacterial counts were determined for the continuously batch-cultured rumen fluid (CRF). The changes in fermentation parameters, NH<sub>3</sub>-N utilization efficiency, and microbial taxa were analyzed in CRF and were compared with that of fresh rumen fluid (RF), frozen rumen fluid (FRF, frozen rumen fluid at −80°C for 1 month), and the mixed rumen fluid (MRF, 3/4 RF mixed with 1/4 CRF) with <italic>in vitro</italic> rumen fermentation.</p></sec><sec id="sec3"><title>Results</title><p>The results showed that the dry matter digestibility remained stable while both the microbial counts and diversity significantly decreased over the 23 days of continuous batch culture. However, the NH<sub>3</sub>-N utilization efficiency of the CRF group was significantly higher than that of RF, FRF, and MRF groups (<italic>p</italic> &lt; 0.05), while five core genera including <italic>Succinivibrio</italic>, <italic>Prevotella</italic>, <italic>Streptococcus</italic>, <italic>F082</italic>, and <italic>Megasphaera</italic> were retained after 23 days of continuous batch culture. The NH<sub>3</sub>-N utilization efficiency was effectively improved after continuous batch culture <italic>in vitro</italic>, and <italic>Streptococcus</italic>, <italic>Succinivibrio</italic>, <italic>Clostridium_sensu_stricto_1</italic>, <italic>p.251.o5</italic>, <italic>Oxalobacter</italic>, <italic>Bacteroidales_UCG.001</italic>, and <italic>p.1088.a5_gut_group</italic> were identified to explain 75.72% of the variation in NH<sub>3</sub>-N utilization efficiency with the RandomForest model.</p></sec><sec id="sec4"><title>Conclusion</title><p>Thus, core bacterial composition and function retained under high urea (5% urea in diet) over 23 days of continuous batch culture <italic>in vitro,</italic> and bacterial biomarkers for ammonia utilization were illustrated in this study. These findings might provide potential applications in improving the efficiency and safety of non-protein nitrogen utilization in ruminants.</p></sec>