Isolation of Thermus strains from hot composts (60 to 80°C)

Abstract

High numbers (107 to 1010 cells per g [dry weight]) of heterotrophic, gram-negative, rod-shaped, non-spore-forming, aerobic, thermophilic bacteria related to the genus Thermus were isolated from thermogenic composts at temperatures between 65 and 82°C. These bacteria were present in different types of wastes (garden and kitchen wastes and sewage sludge) and in all the industrial composting systems studied (open-air windrows, boxes with automated turning and aeration, and closed bioreactors with aeration). Isolates grew fast on a rich complex medium at temperatures between 40 and 80°C, with optimum growth between 65 and 75°C. Nutritional characteristics, total protein profiles, DNA-DNA hybridization (except strain JT4), and restriction fragment length polymorphism profiles of the DNAs coding for the 16S rRNAs (16S rDNAs) showed that Thermus strains isolated from hot composts were closely related to Thermus thermophilus HB8. These newly isolated T. thermophilus strains bare probably adapted to the conditions in the hot- compost ecosystem. Heterotrophic, oval-spore-forming, thermophilic bacilli were also isolated from hot composts, but none of the isolates was able to grow at temperatures above 70°C. This is the first report of hot composts as habitats for a high number of thermophilic bacteria related to the genus Thermus. Our study suggests that Thermus strains play an important role in organic-matter degradation during the thermogenic phase (65 to 80°C) of the composting process.