Influence of the composition of the cellulolytic flora on the development of hydrogenotrophic microorganisms, hydrogen utilization, and methane production in the rumens of gnotobiotically reared lambs

Abstract

We investigated the influence of the composition of the fibrolytic microbial community on the development and activities of hydrogen-utilizing microorganisms in the rumens of gnotobiotically reared lambs. Two groups of lambs were reared. The first group was inoculated with Fibrobacter succinogenes, a non-H(2)-producing species, as the main cellulolytic organism, and the second group was inoculated with Ruminococcus albus, Ruminococcus flavefaciens, and anaerobic fungi that produce hydrogen. The development of hydrogenotrophic bacterial communities, i.e., acetogens, fumarate and sulfate reducers, was monitored in the absence of methanogens and after inoculation of methanogens. Hydrogen production and utilization and methane production were measured in rumen content samples incubated in vitro in the presence of exogenous hydrogen (supplemented with fumarate or not supplemented with fumarate) or in the presence of ground alfalfa hay as a degradable substrate. Our results show that methane production was clearly reduced when the dominant fibrolytic species was a non-H(2)-producing species, such as Fibrobacter succinogenes, without significantly impairing fiber degradation and fermentations in the rumen. The addition of fumarate to the rumen contents stimulated H(2) utilization only by the ruminal microbiota inoculated with F. succinogenes, suggesting that these communities could play an important role in fumarate reduction in vivo.

FIG. 1.

Timeline showing interventions according to the age of the lambs.

FIG. 2.

Ruminal concentrations of acetogens, sulfate-reducing bacteria (SRB), and fumarate-reducing bacteria (FRB) according to the age of the lambs. (A) FS lambs; (B) RAF lambs. For each time point, the results are the means of two most-probable-number (MPN) determinations in each group.

FIG. 3.

Hydrogen production from in vitro incubations of ruminal fluid samples obtained from the two groups of lambs (FS and RAF lambs). The samples were incubated in the presence of ground alfalfa. Values represent means plus standard deviations (SDs) (error bars) from two values for each lamb within each group. Within the same incubation time, values for samples from the two groups were significantly different as follows: *, P < 0.05; **, P < 0.01.

FIG. 4.

In vitro methane (A) and major short-chain fatty acid (SCFA) (B) production after 48 h of incubation of rumen contents from both groups of lambs in the presence of ground alfalfa after establishment of M. wolinii 87-7. The values are the means of two values per lamb with their SDs. The values for the two groups were significantly different (P < 0.001) as indicated by the three asterisks.