Growth of Seeded Escherichia coli in Rewetted Cattle Waste Compost of Different Stages

Dead bacterial biomass-assimilating bacterial populations in compost revealed by high-sensitivity stable isotope probing

Pathogens are known to survive in compost and to regrow under the influence of certain factors, such as moisture content, temperature and nutrient availability. Dead biomass, by providing available nutrients, is a factor that may affect pathogen regrowth. However, the indigenous microorganisms, including pathogens, that grown on the dead biomass of compost have not yet been identified. Here, the regrowth potential of the pathogenic indicator bacterium Escherichia coli in the presence of dead bacterial biomass was determined, and the biomass metabolizers that grew competitively with E. coli were identified by high-sensitivity stable isotope probing of rRNA. Culture-dependent analysis indicated that the addition of dead bacterial biomass did not stimulate E. coli growth. High-throughput analysis of density-resolved 16S rRNA molecules from compost samples amended with carbon-13-labeled dead bacterial biomass revealed dead bacterial-assimilating bacteria, including Sphingobium sp., myxobacterial lineages and Bacillales. These bacteria are potentially competitive with pathogens due to their preferential assimilation of dead biomass in compost.

Insight into the effects of biochar on manure composting: evidence supporting the relationship between N2O emission and denitrifying community

Although nitrous oxide (N2O) emissions from composting contribute to the accelerated greenhouse effect, it is difficult to implement practical methods to mitigate these emissions. In this study, the effects of biochar amendment during pig manure composting were investigated to evaluate the inter-relationships between N2O emission and the abundance of denitrifying bacteria. Analytical results from two pilot composting treatments with (PWSB, pig manure + wood chips + sawdust + biochar) or without (PWS, pig manure + wood chips + sawdust) biochar (3% w/w) demonstrated that biochar amendment not only lowered NO2(-)-N concentrations but also lowered the total N2O emissions from pig manure composting, especially during the later stages. Quantification of functional genes involved in denitrification and Spearman rank correlations matrix revealed that the N2O emission rates correlated with the abundance of nosZ, nirK, and nirS genes. Biochar-amended pig manure had a higher pH and a lower moisture content. Biochar amendment altered the abundance of denitrifying bacteria significantly; less N2O-producing and more N2O-consuming bacteria were present in the PWSB, and this significantly lowered N2O emissions in the maturation phase. Together, the results demonstrate that biochar amendment could be a novel greenhouse gas mitigation strategy during pig manure composting.

Reduction of nitrous oxide emission from pig manure composting by addition of nitrite-oxidizing bacteria

Nitrous oxide (N2O) is emitted from pig manure composting, and the emission correlates with nitrite (NO2-) accumulation in the composting material. In the present study, we added nitrite-oxidizing bacteria (NOB)to inhibit NO2- accumulation and evaluated its effect on N2O emission in a laboratory-scale composting experiment. Mature pig manure compost (MPMC) containing NOB at 10(6) MPN g(-1) WM or cultured MPMC (cul-MPMC) NOB at 10(11) MPN g(-1) WM was added after the thermophilic phase of composting. The addition of these materials prevented NO2- accumulation, promoting oxidation to nitrate (NO3-), whereas the accumulation of NO2- occurred in the material to which NOB was not added as the result of the delayed growth of indigenous NOB compared with that of ammonia-oxidizing bacteria (AOB). The pattern of NO2- in the material agreed with that of N2O emission; therefore, N2O emission ceased rapidly when NOB was added. Emission rates of N2O were 88.5 (no addition), 17.5 (MPMC addition), and 20.2 (cul-MPMC addition) g N-N2O kg(-1) TNinitial, respectively. Improving composition of nitrifying communities for complete nitrification promotion would be useful to establish a composting method with low N2O emission.