- Volume 56, Issue 7, 2006

Three anaerobic, moderately thermophilic, syntrophic primary alcohol- and lactate-degrading microbes, designated strains JLT, JE and OL, were isolated from sludges of thermophilic (55 °C) digesters that decomposed either municipal solid wastes or sewage sludge. The strains were strictly anaerobic organisms. All three strains grew at 25–60 °C and pH 5.5–8.5 and optimum growth was observed at 45–50 °C and pH 6.0–7.0. The three organisms grew chemo-organotrophically on a number of carbohydrates in the presence of yeast extract. In co-culture with the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus, all strains could utilize ethanol, glycerol and lactate syntrophically for growth, although these compounds were not metabolized in pure culture without additional external electron acceptors. All strains could reduce thiosulphate. Quinones were not detected. The DNA G+C contents of strains JLT, JE and OL were 38.0, 37.3 and 37.7 mol%, respectively. Major cellular fatty acids of the strains were iso-C15 : 0, C16 : 0 and unsaturated species of C15 : 1. Phylogenetic analyses based on 16S rRNA gene sequences revealed that the strains belong to a deeply branched lineage of the phylum Firmicutes; the most closely related species was Thermovenabulum ferriorganovorum (16S rRNA gene sequence similarity of 88 %). The three strains were phylogenetically very closely related to each other (99–100 % 16S rRNA gene sequence similarity) and were physiologically and chemotaxonomically similar. These genetic and phenotypic properties suggest that the strains should be classified as representatives of a novel species and genus; the name Tepidanaerobacter syntrophicus gen. nov., sp. nov. is proposed. The type strain of Tepidanaerobacter syntrophicus is strain JLT (=JCM 12098T=NBRC 100060T=DSM 15584T).

Alignment-independent phylogenetic methods have interesting properties for global phylogenetic reconstructions, particularly with respect to speed and accuracy. Here, we present a novel multimer-based alignment-independent bilinear mathematical modelling (AIBIMM) approach for global 16S rRNA gene phylogenetic analyses. In AIBIMM, jackknife cross-validated principal component analyses (PCA) are used to explain the variance in nucleotide n-mer frequency data. We compared AIBIMM with alignment-based distance, maximum-parsimony and maximum-likelihood phylogenetic methods, analysing taxa belonging to the Proteobacteria (n=82), Actinobacteria (n=30) and Archaea (n=7). These analyses indicated an attraction between the Actinobacteria and Archaea for the traditional methods, with the two taxa Acidimicrobium and Rubrobacter at the root of the tree. AIBIMM, on the other hand, showed that the Actinobacteria was tightly clustered, with Acidimicrobium and Rubrobacter within a distinct subgroup of the Actinobacteria. The application of AIBIMM was further evaluated, analysing full-length 16S rRNA gene sequences for 2818 taxa representing the prokaryotic domains. We obtained a highly structured description of the prokaryote diversity. Sample-to-model (Si) distances were also determined for taxa included in our work. We determined Si distances for models of the six major subgroups of taxa detected in the global analyses, in addition to nested subgroups within the Alphaproteobacteria. The Si-distance evaluation showed a very good separation of the taxa within the models from those outside. We conclude that AIBIMM represents a novel phylogenetic framework suitable for accommodating the current exponential growth of 16S rRNA gene sequences in the public domain.