Limnohabitans curvus gen. nov., sp. nov., a planktonic bacterium isolated from a freshwater lake

Abstract

A chemo-organotrophic, aerobic, facultatively anaerobic, non-motile strain, MWH-C5(T), isolated from the water column of the oligomesotrophic Lake Mondsee (Austria), was characterized phenotypically, phylogenetically and chemotaxonomically. The predominant fatty acids of the strain were C(16 : 1)omega7c/omega6c, C(16 : 0), C(12 : 1) and C(8 : 0)-3OH, the major quinone was ubiquinone Q-8 and the G+C content of the DNA of the strain was 55.5 mol%. 16S rRNA gene similarity to the closest related type strains was 96.6 % (Curvibacter delicatus LMG 4328(T)) and 95.7 % (Rhodoferax fermentans FR3(T)). Phylogenetic analysis of 16S rRNA gene sequences revealed the affiliation of the strain with the family Comamonadaceae (Betaproteobacteria); however, the phylogenetic position of the strain did not support an affiliation to any previously described genus within this family. A family-wide comparison of traits revealed that the strain possesses a unique combination of DNA G+C content, major fatty acids and major 3-hydroxy fatty acid. Furthermore, the strain differs in several traits from the closest related genera. Based on the phylogeny of the strain and differences from closely related genera, we propose to establish the new genus and species Limnohabitans curvus gen. nov., sp. nov. to accommodate this strain. The type strain of Limnohabitans curvus is MWH-C5(T) (=DSM 21645(T) =CCUG 56720(T)). The type strain is closely related to a large number of uncultured bacteria detected by cultivation-independent methods in various freshwater systems.

Fig. 1

Electron microscopy image illustrating the cell morphology and size of the strain MWH-C5^T. Cells of a liquid culture were concentrated by centrifugation and fixed with 2.5% glutaraldehyde, post-fixed with OsO₄ and embedded with Spurr resin. Ultra-thin sections were counterstained with uranyl acetate and lead citrate. The image was obtained by transmission electron microscopy at a 20000-fold magnification.

Fig. 2

Neighbour-joining (NJ) tree (Kimura-2 correction) based on almost complete 16S rRNA gene sequences. The tree presents sequences of type species of almost all genera currently affiliated with the family Comamonadaceae. Only Caenibacterium thermophilum, which is proposed by Lütke-Eversloh et al. (2004) to be a later heterotypic synonym of Schlegelella thermodepolymerans (the type species of the genus Schlegelella) is not shown. The genera Polynucleobacter, Duganella, and, Herbaspirillum represent reference taxa not affiliated with the family Comamonadaceae. All Bootstrap values ≥ 60% (1000 iterations) are depicted. The tree was rooted by using archeal sequences (not shown). Bar, 5 nucleotide substitution per 100 nucleotides.