The molecular diversity and community structure of bacteria from the gut of the termite Reticulitermes speratus were analyzed by the sequencing of near-full-length 16S rRNA genes, amplified by polymerase chain reaction. The results of the analysis of 1344 clones indicated a predominance of spirochetes in the gut. Spirochetal clones accounted for approximately half of the analyzed clones. The clones related to Bacteroides, Clostridia, and the candidate division Termite Group I each accounted for approximately 5-15% of the analyzed clones. The rest were comprised of Proteobacteria, Actinobacteria, Mycoplasma and others. Using the criterion of 97% sequence identity, the clones were sorted into 268 phylotypes, including 100 clostridial, 61 spirochetal and 31 Bacteroides-related phylotypes. More than 90% of the phylotypes were found for the first time, and some constituted monophyletic clusters with sequences recovered from the gut of other termite species.