Effects of lysozyme on in vitro fermentation, methanogenesis and microbial community structure of the rumen

Abstract:

[Objective] We studied the effects of lysozyme on in vitro rumen fermentation, methanogenesis and microbial community structure. [Methods] Lysozyme was added to in vitro ruminal cultures at 5 doses: with 0 (L-0, Control), 0.1 mg/100 mL (L-0.1), 1 mg/100 mL (L-1), 10 mg/100 mL (L-10), and 100 mg/100 mL (L-100). Total gas and methane production were measured at different time of incubation. Culture samples were collected at 24 h for analysis of fermentation parameters and functional microbial populations. In addition, samples of L-0, L-1, and L-100 collected at 24 h were also used subjected to metagenomics analysis of bacterial community using Illumina sequencing of 16S rRNA gene amplicons. [Results] Compared with control, methane production, ammonia concentration, dry matter digestibility, organic matter digestibility and total volatile fatty acid concentration were not influenced by L-0.1 (P>0.05). Methane production and NH₃-N concentration were reduced, and propionate concentration was increased by L-1 (P<0.05), whereas dry matter digestibility, organic matter digestibility or total volatile fatty acid were not affected (P>0.05). Methane production was reduced, and propionate concentration was increased by L-10 and L-100 (P<0.05), but dry matter digestibility and organic matter digestibility were also decreased significantly (P<0.05). The qPCR results showed that total bacteria, fungi and methanogens were significantly reduced by L-100 (P<0.05), but were not influenced (P>0.05) by L-0.1, L-1, or L-10. Principal Component Analysis of the sequencing data showed clear differences in the composition of the ruminal bacterial community between the control and the lysozyme treatments, demonstrating evident impact of the lysozyme addition. The abundance of propionate-producing bacteria (e.g., Selenomonas and Succinivibrio) was increased by lysozyme, resulting in more hydrogen being directed to production of propionate instead of methane. Moreover, the reduced ammonia concentration in L-1 was probably due to the lower abundance of proteolytic bacteria (e.g., Prevotella and Bacteroides) inhibited by lysozyme. [Conclusion] Appropriate lysozyme addition (1 mg/100 mL) can be used to modulate ruminal microbial ecology and reduce methanogenesis and ammoniagenesis by rumen microbiome without adversely affecting feed digestion or fermentation in short-term.s