Publications

4366

The taxonomic position of a group of mesophilic actinomycetes isolated from arid Australian soils was determined using a polyphasic approach. The organisms shared chemical and morphological markers typical of members of the genusAmycolatopsis. They had identical 16S rRNA gene sequences and formed a distinct phyletic line in theAmycolatopsis mediterraneiclade, being most closely related toA. mediterranei. In addition, they shared a range of phenotypic properties that distinguished them from representatives of all of the species classified in this clade. The combined genotypic and phenotypic data indicate that the strains merit species status within the genusAmycolatopsis. The name proposed for the novel species isAmycolatopsis australiensissp. nov.; the type strain is GY048T(=DSM 44671T=NCIMB 14142T).

Despite differences in their morphologies, comparative analyses of 16S rRNA gene sequences revealed high levels of similarity (>94 %) between strains of the filamentous bacterium ‘CandidatusNostocoida limicola’ and the cocciTetrasphaera australiensisandTetrasphaera japonicaand the rodTetrasphaera elongata, all isolated from activated sludge. These sequence data and their chemotaxonomic characters, including cell wall, menaquinone and lipid compositions and fingerprints of their 16S–23S rRNA intergenic regions, support the proposition that these isolates should be combined into a single genus containing six species, in the familyIntrasporangiaceaein theActinobacteria. This suggestion receives additional support from DNA–DNA hybridization data and when partial sequences of therpoC1gene are compared between these strains. Even though few phenotypic characterization data were obtained for these slowly growing isolates, it is proposed, on the basis of the extensive chemotaxonomic and molecular evidence presented here, that ‘CandidatusN. limicola’ strains Ben 17, Ben 18, Ben 67, Ben 68 and Ben 74 all be placed into the speciesTetrasphaera jenkinsiisp. nov. (type strain Ben 74T=DSM 17519T=NCIMB 14128T), ‘CandidatusN. limicola’ strain Ben 70 intoTetrasphaera vanveeniisp. nov. (type strain Ben 70T=DSM 17518T=NCIMB 14127T) and ‘CandidatusN. limicola’ strains Ver 1 and Ver 2 intoTetrasphaera veronensissp. nov. (type strain Ver 1T=DSM 17520T=NCIMB 14129T).

Summary Twelve strains of filamentous bacteria morphologically identified as ‘ Microthrix parvicella ’ were isolated from industrial activated sludge wastewater treatment plants. 16S rRNA gene sequences analysis showed that these strains were all closely related to ‘ Candidatus Microthrix parvicella’. Six of them, however, had a 16S rRNA gene similarity of only 95.7% and 96.7% to ‘ Candidatus Microthrix parvicella’ suggesting the presence of a new species. The name ‘ Candidatus Microthrix calida’ is proposed for this new microorganism. The physiological properties of these six isolates supported the description of a new taxon. The ‘ Candidatus Microthrix calida’ strains produced thin filaments (0.3–0.7 µm diameter), they did not grow on the media supporting the growth of ‘ Candidatus Microthrix parvicella’ and could be cultivated at higher temperature (up to 36.5°C). Preliminary data on substrate uptake were obtained by microautoradiography on pure culture. Two new fluorescence in situ hybridization (FISH) probes, Mpa‐T1‐1260 specific for ‘ Candidatus Microthrix calida’ and Mpa‐all‐1410 targeting both Microthrix species, were designed. The presence of Microthrix spp. was investigated in 114 activated sludge plants. ‘ Microthrix parvicella ’ morphotype was detected in 23% of the analysed samples and FISH analysis revealed that ‘ Candidatus Microthrix calida’ was present in 5% of them. The remaining ‘ M. parvicella ’ filaments were positive with probe Mpa‐all‐1410 but could not all be identified as ‘ Candidatus Microthrix parvicella’ suggesting the presence of more hitherto undescribed biodiversity within this morphotype.