Thermophilic bacterial communities in hot composts as revealed by most probable number counts and molecular (16S rDNA) methods

Thermogenic composts are known to host a variety of thermophilic micro-orga nisms that were recently investigated by cultural means and identified as T hermus thermophilus, Bacillus spp., and Hydrogenobacter spp. In this paper, we present a classical, cultural enumeration of thermophilic populations o n the one hand, and a molecular investigation of the bacterial community by restriction enzyme analyses of a clone library of bacterial 16S rRNA genes on the other hand. Bacterial diversity, revealed by the clone analyses of four samples, was shown to undergo a dramatic change between the young (13- 18-day) and the old (39-41-day) samples, possibly linked to the general dec rease in temperature and the physicochemical evolution of organic matter du ring the composting process. Among the 200 clones investigated, 69 clones c ould be identified as Thermus thermophilus and thermophilic Bacillus spp. T hese results proved both taxa to be among the dominant bacterial population s at the highest temperatures reached by thermogenic composts. (C) 1999 Pub lished by Elsevier Science B.V. All rights reserved.