Effects of chromium(III) on enzyme activities and bacterial communities during swine manure composting

The present study investigated the effects of different concentrations of chromium (i.e., 200 and 700 mg kg−1 Cr corresponding to Cr200 and Cr700, respectively) on the microorganisms in swine manure compost. The results demonstrated that a high concentration of Cr(III) could inhibit the activity of key microbial enzymes (i.e., dehydrogenase, cellulase, and urease) in the early composting stages, with maximal inhibition rates of 54.9%, 32.8%, and 46.7% for cellulase, urease, and dehydrogenase, respectively. Furthermore, the bacterial abundances were determined by quantitative PCR and their compositions were evaluated by denaturing gradient gel electrophoresis. Cr200 and Cr700 had significant inhibitory effects on the abundances of bacteria. The DGGE results showed that Cr200 and Cr700 changed the bacterial community structure and diversity, where Cr(III) might enhance the abundance of pathogenic bacteria (e.g., Saccharomonospora) and decrease the abundances of bacteria that degrade cellulose and lignin (e.g., Paenibacillus) during composting.