Isolation and characterization of highly thermophilic xylanolytic Thermus thermophilus strains from hot composts

This is the first detailed report of xylanolytic activity in Thermus strains. Two highly thermophilic xylanolytic bacteria, very closely related to non-xylanolytic T. thermophilus strains, have been isolated from the hottest zones of compost piles. Strain X6 was investigated in more detail. The growth rate (optical density monitoring) on xylan was 0.404.h-1 at 75 degrees C. Maximal growth temperature was 81 degrees C. Xylanase activity was mainly cell-bound, but was solubilized into the medium by sonication. It was induced by xylan or xylose in the culture medium. The temperature and pH optima of the xylanases were determined to be around 100 degrees C and pH 6, respectively. Xylanase activity was fairly thermostable; only 39% of activity was lost after an incubation period of 48 h at 90 degrees C in the absence of substrate. Xylanolytic T. thermophilus strains could contribute to the degradation of hemicellulose during the thermogenic phase of industrial composting.