Evolution of extracellular enzyme activities during manure composting

Aims: The objectives of this work were to determine the extracellular enzyme profiles during composting, relate the activities of these enzymes to the changes in microbial population and compare the enzyme profiles between two manures. Methods and Results: API ZyM(TM) assay was used to monitor the activities of 19 extracellular enzymes during poultry and pig manure composting. Results showed an overall increase in diversity and relative abundance of enzymes present. The relative abundance and activities of enzymes were higher in poultry manure than in pig manure. Among the 19 enzymes tested, esterase, valine amino-peptidase and alpha-galactosidase were the most abundant enzymes in poultry manure, whereas it was N-acetyl-beta-glucosaminidase for the pig manure. A number of these enzymes correlated with change in numbers of different microbial groups during composting. Conclusions: The composting process represented a combined activity of a wide succession of environments, as one enzyme/microbial group overlapped the other and each emerged gradually due to the continual change in temperature and progressive breakdown of complex compounds to simpler ones. Significance and Impact of the Study: The results presented here show the applicability of the API ZYM(TM) test not only in monitoring the quantitative and qualitative fluctuation of the available substrate during composting, but also in revealing differences in composts and compost maturity.