Amplified 16S Ribosomal DNA Restriction Analysis of Microbial Community Structure During Rapid Degradation of a Biopolymer, PHA, by Composting

Abstract

To investigate the changes in the microbial community structure during composting and to compare the differences in the structures between different composting processes, amplified ribosomal DNA restriction analysis (ARDRA) patterns of entire microbial communities were developed. Rapid degradation of polyhydroxyalkanoates (PHAs) in a model composting process was studied by changing the operation conditions and initial conditions as well as by addition of PHA-degrading microorganisms. Azotobacter sp. AZ34, which was isolated from our compost and could degrade PHA, was added at high concentrations at the beginning of composting. The differences in ARDRA patterns between composting with and without addition of the bacteria were investigated. There was a significant difference in microbial community structures between the two cases at the early stage, but ARDRA patterns at the middle and final stages appeared to be almost the same. No effect was observed at least in terms of PHA degradation rate compared, between AZ34 and the control, which was primed with the seed compost without addition of PHA-degrading bacteria. After autoclaving the raw materials of the compost, AZ34 was initially added and the seed compost was added at 72 hours and composting process continued. The effect of the PHA-degrading bacteria was observed, in this case. This experiment demonstrated that if the initial microbial population in the raw materials of the compost is significantly reduced, AZ34 can grow preferentially and promotes PHA degradation during the composting process. The same effect as that observed in this experiment was found by recycling fairly large amounts of the compost. This finding of the preferential growth of microorganisms in a microbial community will be utilized for the production of functional composts.