Effect of the addition of Peptostreptococcus productus ATCC 35244 on reductive acetogenesis in the ruminal ecosystem after inhibition of methanogenesis by cell-free supernatant of Lactobacillus plantarum 80

The addition of the cell-free supernatant of Lactobacillus plantarum 80 (LP80) to ruminal samples during short-term batch experiments (24 h) led to significant increases in volatile fatty acid (VFA) production (5–30%) and to significant decreases in CH4 production (5–15%), accompanied by H2 accumulation. The supplemental addition of the reductive acetogen Peptostreptococcus productus ATCC35244 gave rise to an additional increase in VFA production, while CH4 production was decreased further (p<0.01) and H2 accumulation was abolished. The addition of P. productus without the addition of supernatant had no effect on the fermentation patterns. The utilization of H2, the lowering of the H2 recovery (2Hr) value and the high acetate production observed in the experiment indicated that both the addition of either the supernatant or the addition of the supernatant and P. productus stimulated reductive acetogenesis. The persistence of the obtained effects was further evaluated in vitro by incubation of rumen contents under pH control (6.4–6.6) during 72 h. Compared to short-term batch experiments, the stimulation of VFA production was lower (8–15%), while inhibition of CH4 production was higher (18–30%). These effects became manifest during the first 24 h of incubation and persisted during the 72 h incubation period. Infusion of both supernatant of LP80 and P. productus in the rumen of two rumen fistulated rams revealed that during the first days of administration, the addition of supernatant and P. productus decreased methanogenesis much more strongly than was observed in vitro (80%), whereas no clear effect on fermentation rate or patterns was observed. However, the effect was only transient, since at the sixth day of the administration period methanogenesis was again at the same level as during the control period. These results indicate that the supernatant of LP80 contains compounds which inhibit methanogenesis in the rumen, but that either resistance to the compound, or stimulation of rumen microbial breakdown of these compounds had occurred. Also, the ability to stimulate reductive acetogenesis by additional introduction of P. productus was only important during short-term incubations, while the effect diminished during long-term in vitro incubations or disappeared in vivo.