Distribution of ammonia assimilating bacteria in the composting process

Ammonia assimilating bacteria were isolated from composting processes and their abilities to assimilate ammonia were evaluated. In the prefermentation stage of the composting, 10^4.7 and 10^3.7 (CFU/g) of ammonia assimilating bacteria were detected on the medium which contained ammonia as a sole nitrogen, at 37°C and 55°C, respectively. They were 10^4.6 and 10^3.2 in the end of the primary fermentation, and 10^5.1 and 10^3.2 in the end of the secondary fermentation, respectively. When isolates were purely cultivated in sterilized compost extract medium, many of them consumed ammonia not by nitrification but by assimilation. They still assimilated ammonia even in nonsterilized compost extract medium, i.e. mixed culture with the live microbial flora of the compost. However, isolates which showed high ammonia assimilating ability in the pure culture did not always show high abilities in nonsterilized compost extract media. Isolates which showed high ammonia assimilating ability in the nonsterilized medium were identified by analysis of 16S ribosomal DNA. Dominant species of ammonia assimilating microorganisms varied as composting proceeded.