ISOLATION OF THERMUS STRAINS FROM HOT COMPOSTS (60 TO 80-DEGREES-C)

High numbers (10(7) to 10(10) cells per g [dry weight]) of heterotroph ic, gram-negative, rod-shaped, non-spore-forming, aerobic, thermophili c bacteria related to the genus Thermus were isolated from thermogenic composts at temperatures between 65 and 82 degrees C, These bacteria were present in different types of wastes (garden and kitchen wastes a nd sewage sludge) and in all the industrial composting systems studied (open-air windrows, boxes with automated turning and aeration, and cl osed bioreactors with aeration), Isolates grew fast on a rich complex medium at temperatures between 40 and 80 degrees C, with optimum growt h between 65 and 75 degrees C, Nutritional characteristics, total prot ein profiles, DNA-DNA hybridization (except strain JT4), and restricti on fragment length polymorphism profiles of the DNAs coding for the 16 S rRNAs (16S rDNAs) showed that Thermus strains isolated from hot comp osts were closely related to Thermus thermophilus HB8. These newly iso lated T. thermophilus strains have probably adapted to the conditions in the hot-compost ecosystem, Heterotrophic, oval-spore-forming, therm ophilic bacilli were also isolated from hot composts, but none of the isolates was able to grow at temperatures above 70 degrees C. This is the first report of hot composts as habitats for a high number of ther mophilic bacteria related to the genus Thermus. Our study suggests tha t Thermus strains play an important role in organic-matter degradation during the thermogenic phase (65 to 80 degrees C) of the composting p rocess.