AUTHOR=Zhong Huimin , Zhou Jiayan , Wang Fan , Wu Wenqing , Xiong Haiqian , Yin Huaihui , Li Xiang 

TITLE=Isolation and identification of ligninolytic bacterium (Bacillus cereus) from buffalo (Bubalus bubalis) rumen and its effects on the fermentation quality, nutrient composition, and bacterial community of rape silage

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1103652

DOI=10.3389/fmicb.2023.1103652

ISSN=1664-302X

ABSTRACT=<p>This study aimed to isolate and identify a ligninolytic bacterium from the rumen of buffalo (<italic>Bubalus bubalis</italic>) and investigate its effects as a silage additive for whole-plant rape. Three lignin-degradation strains were isolated from the buffalo rumen, with AH7-7 being chosen for further experiments. Strain AH7-7, with acid tolerance and a 51.4% survival rate at pH 4, was identified as <italic>Bacillus cereus</italic>. It exhibited a lignin-degradation rate of 20.5% after being inoculated in a lignin-degrading medium for 8 days. We divided the rape into four groups according to the various additive compositions to examine the fermentation quality, nutritional value, and bacterial community after ensiling: Bc group (inoculated with <italic>B. cereus</italic> AH7-7 3.0 × 10<sup>6</sup> CFU g FW<sup>−1</sup>), Blac group (inoculated with <italic>B. cereus</italic> AH7-7 1.0 × 10<sup>6</sup> CFU g FW<sup>−1</sup>, <italic>L. plantarum</italic> 1.0 × 10<sup>6</sup> CFU g FW<sup>−1</sup>, and <italic>L. buchneri</italic> 1.0 × 10<sup>6</sup> CFU g FW<sup>−1</sup>), Lac group (inoculated with <italic>L. plantarum</italic> 1.5 × 10<sup>6</sup> CFU g FW<sup>−1</sup> and <italic>L. buchneri</italic> 1.5 × 10<sup>6</sup> CFU g FW<sup>−1</sup>), and Ctrl group (no additives). After 60 days of fermentation, the application of <italic>B. cereus</italic> AH7-7 was potent in modulating the fermentation quality of silage, especially when combined with <italic>L. plantarum</italic> and <italic>L. buchneri</italic>, as indicated by lower dry matter loss and higher contents of crude protein, water-soluble carbohydrate, and lactic acid. Furthermore, treatments with the <italic>B. cereus</italic> AH7-7 additive decreased the contents of acid detergent lignin, cellulose, and hemicellulose. The <italic>B. cereus</italic> AH7-7 additive treatments reduced the bacterial diversity and optimized the bacterial community compositions of silage, with an increase in the relative abundance of beneficial <italic>Lactobacillus</italic> and a decrease in the relative abundance of undesirable <italic>Pantoea</italic> and <italic>Erwinia</italic>. Functional prediction revealed that inoculation with <italic>B. cereus</italic> AH7-7 could increase the cofactors and vitamins metabolism, amino acid metabolism, translation, replication and repair, and nucleotide metabolism, while decreasing the carbohydrate metabolism, membrane transport, and energy metabolism. In brief, <italic>B. cereus</italic> AH7-7 improved the microbial community, fermentation activity, and ultimately the quality of silage. The ensiling with <italic>B. cereus</italic> AH7-7, <italic>L. plantarum</italic>, and <italic>L. buchneri</italic> combination is an effective and practical strategy to improve the fermentation and nutrition preservation of rape silage.</p>