Chicken Manure Methanogenesis.: 2. Differential Inhibition of Methanogenesis from Acetate by Monensin, Lasalocid, and Broiler Litter Extracts

Abstract

A thermophilic (55 C) acetate-enriched methanogenic culture was obtained in order to study the differential inhibition phenomena observed in chicken manure methane fermentation. The substrate range, temperature optima, and morphology of the culture, which was apparently dominated by Methanosarcina species, were recorded. Effects were reported of different concentrations of the carboxylic ionophores monensin and lasalocid on methane formation by the growing culture from acetate and from H2/CO2. Significantly (P<.01) greater sensitivity was observed for methanogenesis from acetate compared with that from H2/CO2 in a specified ionophore concentration range. In order to establish the validity of this experimental model system in reflecting the inhibition observed for broiler litter, the effects of a manure water extract and its subfractions also were examined using 2-[14 C]acetate or H2/CO2 as the methanogenic substrate. The existence of selective inhibition of methanogenesis from acetate clearly (P<.001) was shown by the water extract and by its organic solvent soluble subfractions, as well as by the pure ionophores. Furthermore, chromatographic fractionation gave strong indication that broiler litter extracts contained monensin at levels which proved to be inhibitory. A decrease of Na+ concentration in the medium also was found to be detrimental to acetate decarboxylation, but did not interfere with H2 oxidation to methane. The combination of low Na+ concentrations and subinhibitory concentration of monensin inhibited both methanogenic activities.