Aims: To demonstrate the occurrence of cellulolytic bacteria in the termite Zootermopsis angusticollis. Methods and Results: Applying aerobic cultivation conditions we isolated 119 cellulolytic strains from the gut of Z. angusticollis, which were assigned to 23 groups of aerobic, facultatively anaerobic or microaerophilic cellulolytic bacteria. 16S rDNA restriction fragment pattern and partial 16S rDNA sequence analysis, as well as numerical taxonomy, were used for the assignment of the isolates. The Gram-positive bacteria of the actinomycetes branch could be assigned to the order Actinomycetales including the genera Cellulomonas/Oerskovia, Microbacterium and Kocuria. The Gram-positive bacteria from the order Bacillales belonged to the genera Bacillus, Brevibacillus and Paenibacillus. Isolates related to the genera A®pia, Agrobacterium/Rhizobium, Brucella/Ochrobactrum, Pseudomonas and Sphingomonas/Zymomonas from the a-proteobacteria and Spirosoma-like from the``Flexibacteriaceae'' represented the Gram-negative bacteria. Conclusions: A cell titre of up to 10 7 cellulolytic bacteria per ml, determined for some isolates, indicated that they may play a role in cellulose digestion in the termite gut in addition to the cellulolytic¯agellates and termite's own cellulases. Signi®cance and Impact of the Study: The impact of bacteria on cellulose degradation in the termite gut has always been a matter of debate. In the present survey we investigated the aerobic and facultatively anaerobic cellulolytic bacteria in the termite gut.

We examined the abundance and spatial distribution of major phylogenetic groups of the domain Bacteria in hindguts of the Australian lower termite Mastotermes darwiniensis by using in situ hybridization with group-specific, fluorescently labeled, rRNA-targeted oligonucleotide probes. Between 32.0 +/- 7.2% and 52.3 +/- 8.2% of the DAPI-stained cells in different hindgut fractions were detected with probe EUB338, specific for members of the domain Bacteria. About 85% of the prokaryotic cells were associated with the flagellates of the thin-walled anterior region (P3a) and the thick wall of the posterior region (P3b/P4) of the hindgut, as shown by DAPI staining. At most, half of the EUB338-detected cells hybridized with one of the other probes that targeted a smaller assemblage within the bacterial domain. In most fractions, cells were found in varying numbers with probe ALF1b, which targeted members of the alpha-Proteobacteria, whereas substantial amounts of sulfate-reducing bacteria, gram-positive bacteria with a high DNA G+C content and members of the Cytophaga-Flavobacterium cluster of the Cytophaga-Flavobacterium-Bacteroides (CFB) phylum could be detected only in the wall fraction of P3b/P4. This clearly indicates that the hindgut microhabitats differ in the composition of their microbial community. In situ hybridization of cryosections through the hindgut showed only low numbers of bacteria attached to the P3a wall. In contrast, the wall of P3b was densely colonized by rod- and coccus-shaped bacteria, which could be assigned to the Cytophaga-Flavobacterium cluster of the CFB phylum and to the group of gram-positive bacteria with a high DNA G+C content, respectively. Oxygen concentration profiles determined with microelectrodes revealed steep oxygen gradients both in P3a and P3b. Oxygen was consumed within 100 &mgr;m below the gut surface, and anoxic conditions prevailed in the central portions of both gut regions, indicating that oxygen consumption in the hindgut does not depend on the presence of a biofilm on the hindgut wall.

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A novel cellulolytic and xylanolytic bacterium, strain MX5T, was isolated from the hindgut contents of the Australian termite Mastotermes darwiniensis (Froggatt). The isolate was a facultative anaerobe and had a Gram-positive cell-wall profile. The rod-shaped bacterium formed irregular coryneform and coccoid cells during growth. Phylogenetic analysis of the 16S rDNA provided evidence that the organism was closely related to the as-yet undescribed cellulolytic strain SR272 and the non-validly described species 'Cellulomonas pachnodae' as well as Promicromonospora citrea and Promicromonospora sukumoe. Strain MX5T was assigned to the genus Cellulosimicrobium on the basis of phylogenetic and chemotaxonomic criteria. The murein of strain MX5T contained the diamino acid lysine. N-Glycolylmuramic acid, mycolic acids and hydroxy fatty acids were absent. The major neutral sugar in the cell wall was galactose and the major quinone was menaquinone MK-9(H4). The predominant fatty acids were ai-C15:0, i-C15:0, i-C16:0 and C16:0. The G+C content of the DNA was in a range 70-72 mol%. On the basis of 16S rDNA sequence similarities and chemotaxonomic features, MX5T was clearly different from Cellulosimicrobium cellulans and other validly described species within this phylogenetic group. For this reason, a novel species is described, for which the name Cellulosimicrobium variabile sp. nov. is proposed.