Effect of Escherichia coli W3110 on ruminal methanogenesis and nitrate/nitrite reduction in vitro

An in vitro continuous incubation system was used to evaluate effects of nitrate, nitrite and wild-type Escherichia coli W3110 on in vitro methanogenesis by mixed ruminal population, and to determine the reducing ability of wild-type E. coli W3110 on in vitro nitrate/nitrite reduction. The culture mixture consisted of 400 ml of strained rumen fluid from two non-lactating Holstein cows fed a diet of orchardgrass hay at maintenance level, and 400 ml of autoclaved buffer solution. The treatments consisted of nitrate (NaNO3, 5 or 10 mM), nitrite (NaNO2, 1 or 2 mM), inoculated E. coli W3110, nitrate (NaNO3, 5 or 10 mM) plus E. coli W3110, and nitrite (NaNO2, 1 or 2 mM) plus E. coli W3110. The control culture was incubated without supplements. Methanogenesis was markedly decreased by addition of nitrate and nitrite, and inoculation of E. coli W3110-reduced methanogenesis by 27%. Inoculation of E. coli W3110 to nitrite containing cultures decreased nitrite accumulation, while keeping methanogenesis low. The culture of wild-type E. coli W3110 may decrease methanogenesis in cultures of mixed rumen microbes, suggesting that inoculation of wild-type E. coli W3110 may be a practical way to suppress nitrite toxicity when nitrite is used to abate methanogenesis in the rumen.