PSXIV-16 Comparative in vitro effects of spray-dried and freshly-harvested Paenibacillus fortis strain 79R4 on rumen methane, nitrate, nitrite and ammonia metabolism
Abstract Nitrate supplementation into the ruminant diet can decrease ruminal methane emissions, but amounts needed to achieve appreciable decreases can risk ruminal accumulations of nitrite with potential for methemoglobinemia. A denitrifying rumen Paenibacillus fortis strain 79R4 (79R4) selected for enhanced nitrite-metabolizing ability has shown promise as a probiotic to decrease risks of nitrite toxicosis. Presently, a spray-dried prototype of this spore-forming, facultative anaerobe was tested during anaerobic culture (10 mL/tube) of rumen fluid freshly-collected from an alfalfa hay-fed cannulated Jersey cow. Cultures supplemented with 22 mM sodium nitrate and without or with inoculations of freshly-harvested (FH) cells or spray dried (SP) 79R4 spores (3 tubes/treatment; 108 cells/spores per tube) were cultured anaerobically (39oC for 24 h with 100% CO2). The FH- and SP- cells were grown aerobic, 72 h in tryptic soy broth, SP- cells were then processed and spray-dried. Nitrate-supplementation decreased (P = 0.0006; SEM = 0.31) methane production by the cultures, but this decrease was unaffected by 79R4 inoculation (2.57 µmol CH4/mL with no nitrate/no inoculum versus 0.15 µmol CH4/mL with nitrate/inoculum). Nitrate-metabolizing activity in nitrate-treated cultures were unaffected by 79R4 inoculations (P = 0.17; SEM = 0.15), rates being 0.95, 0.63 and 0.50 µmol nitrate/mL h-1 FH-, SP- and non-inoculated cultures, respectively. Nitrite accumulation rates (P = 0.10; SEM = 0.06) and peak nitrite concentrations (P = 0.06; SEM = 0.75) tended to be lower in SP- than in FH- and non-inoculated cultures (0.29, 0.47 and 0.47 µmol nitrite/mL h-1 and 3.33, 5.67 and 5.66 µmol/mL, respectively). Rates of ammonia accumulation were more rapid (P = 0.01; SEM = 0.01) in SP- and FH- than in non-inoculated cultures (0.16 and 0.15 versus 0.06 µmol/mL h-1, respectively). Results provide evidence that 79R4 prototype may aid rumen populations in detoxifying nitrite, therefore enhancing the abilities of high nitrate diets.
