Isolation and identification of bacteria from high-temperature compost at temperatures exceeding 90C

Conventional composts exhibit temperatures ranging from 50 to 80°C during organic waste degradation by microorganisms. In high-temperature compost, temperatures can reach ≥90°C with appropriate bottom aeration. To elucidate specific characteristics of the bacterial activity in high-temperature compost and to regenerate a high-temperature compost from isolates, bacterial isolation and characterization were performed. Although the isolated taxa varied depending on sample and temperature, the use of gellan gum medium and cultivation at 60°C led to high diversity among the isolated taxa. In addition, combining the use of the compost extract with water-solvent medium led to the isolation of more diverse species. Based on 16S rRNA gene sequencing, the isolates shared ≥99% similarity with Geobacillus thermodenitrificans, Ureibacillus spp. (Ureibacillus suwonensis, Ureibacillus themosphaericus) and Aeribacillus pallidus, and these isolates were isolated from both steady-state and newly prepared small-scale composts. Thus, these taxa were considered to be frequently observed regardless of the composting process. Although the frequency of isolation of mesophilic bacteria from this high-temperature compost was lower than that from ordinary composts, these bacteria have been isolated from ordinary composts and there was a discrepancy between the in situ compost temperature (≥90°C) and their maximum growth temperature (≤70°C).