The application of phylogenetic taxonomic procedures led to improvements in the classification of bacteria assigned to the phylum Actinobacteria but even so there remains a need to further clarify relationships within a taxon that encompasses organisms of agricultural, biotechnological, clinical, and ecological importance. Classification of the morphologically diverse bacteria belonging to this large phylum based on a limited number of features has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees. Here, draft genome sequences of a large collection of actinobacterial type strains were used to infer phylogenetic trees from genome-scale data using principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families, and genera, as well as many species and a few subspecies were shown to be in need of revision leading to proposals for the recognition of 2 orders, 10 families, and 17 genera, as well as the transfer of over 100 species to other genera. In addition, emended descriptions are given for many species mainly involving the addition of data on genome size and DNA G+C content, the former can be considered to be a valuable taxonomic marker in actinobacterial systematics. Many of the incongruities detected when the results of the present study were compared with existing classifications had been recognized from 16S rRNA gene trees though whole-genome phylogenies proved to be much better resolved. The few significant incongruities found between 16S/23S rRNA and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences. Similarly good congruence was found between the discontinuous distribution of phenotypic properties and taxa delineated in the phylogenetic trees though diverse non-monophyletic taxa appeared to be based on the use of plesiomorphic character states as diagnostic features.

The bacterial phylum Bacteroidetes, characterized by a distinct gliding motility, occurs in a broad variety of ecosystems, habitats, life styles, and physiologies. Accordingly, taxonomic classification of the phylum, based on a limited number of features, proved difficult and controversial in the past, for example, when decisions were based on unresolved phylogenetic trees of the 16S rRNA gene sequence. Here we use a large collection of type-strain genomes from Bacteroidetes and closely related phyla for assessing their taxonomy based on the principles of phylogenetic classification and trees inferred from genome-scale data. No significant conflict between 16S rRNA gene and whole-genome phylogenetic analysis is found, whereas many but not all of the involved taxa are supported as monophyletic groups, particularly in the genome-scale trees. Phenotypic and phylogenomic features support the separation of Balneolaceae as new phylum Balneolaeota from Rhodothermaeota and of Saprospiraceae as new class Saprospiria from Chitinophagia. Epilithonimonas is nested within the older genus Chryseobacterium and without significant phenotypic differences; thus merging the two genera is proposed. Similarly, Vitellibacter is proposed to be included in Aequorivita. Flexibacter is confirmed as being heterogeneous and dissected, yielding six distinct genera. Hallella seregens is a later heterotypic synonym of Prevotella dentalis. Compared to values directly calculated from genome sequences, the G+C content mentioned in many species descriptions is too imprecise; moreover, corrected G+C content values have a significantly better fit to the phylogeny. Corresponding emendations of species descriptions are provided where necessary. Whereas most observed conflict with the current classification of Bacteroidetes is already visible in 16S rRNA gene trees, as expected whole-genome phylogenies are much better resolved.

Although considerable progress has been made in recent years regarding the classification of bacteria assigned to the phylum Bacteroidetes, there remains a need to further clarify taxonomic relationships within a diverse assemblage that includes organisms of clinical, piscicultural, and ecological importance. Bacteroidetes classification has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees and a limited number of phenotypic features. Here, draft genome sequences of a greatly enlarged collection of genomes of more than 1,000 Bacteroidetes and outgroup type strains were used to infer phylogenetic trees from genome-scale data using the principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families and genera, including taxa proposed long ago such as Bacteroides, Cytophaga, and Flavobacterium but also quite recent taxa, as well as a few species were shown to be in need of revision. According proposals are made for the recognition of new orders, families and genera, as well as the transfer of a variety of species to other genera. In addition, emended descriptions are given for many species mainly involving information on DNA G+C content and (approximate) genome size, both of which can be considered valuable taxonomic markers. We detected many incongruities when comparing the results of the present study with existing classifications, which appear to be caused by insufficiently resolved 16S rRNA gene trees or incomplete taxon sampling. The few significant incongruities found between 16S rRNA gene and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences and the impediment in using ordinary bootstrapping in phylogenomic studies, particularly when combined with too narrow gene selections. While a significant degree of phylogenetic conservation was detected in all phenotypic characters investigated, the overall fit to the tree varied considerably, which is one of the probable causes of misclassifications in the past, much like the use of plesiomorphic character states as diagnostic features.

Longimicrobium terrae gen. nov., sp. nov., an oligotrophic bacterium of the under-represented phylum Gemmatimonadetes isolated through a system of miniaturized diffusion chambers A novel chemo-organoheterotroph bacterium, strain CB-286315 T , was isolated from a Mediterranean forest soil sampled at the Sierra de Tejeda, Almijara and Alhama Natural Park, Spain, by using the diffusion sandwich system, a device with 384 miniature diffusion chambers. 16S rRNA gene sequence analyses identified the isolate as a member of the under-represented phylum Gemmatimonadetes, where 'Gemmatirosa kalamazoonensis' KBS708, Gemmatimonas aurantiaca T-27 T and Gemmatimonas phototrophica AP64 T were the closest relatives, with respective similarities of 84.4, 83.6 and 83.3 %. Strain CB-286315 T was characterized as a Gram-negative, non-motile, short to long rod-shaped bacterium. Occasionally, some cells attained an unusual length, up to 35-40 mm. The strain showed positive responses for catalase and cytochrome-c oxidase and division by binary fission, and exhibited an aerobic metabolism, showing optimal growth under normal atmospheric conditions. Strain CB-286315 T was also able to grow under micro-oxic atmospheres, but not under anoxic conditions. The strain is a slowly growing bacterium able to grow under low nutrient concentrations. Major fatty acids included iso-C 17 : 1 v9c, summed feature 3 (C 16 : 1 v7c and/or iso-C 15 : 0 2-OH), C 16 : 0 and iso-C 17 : 0 . The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, two unidentified glycolipids and three phospholipids. The major isoprenoid quinone was MK-8 and the diagnostic diamino acid was meso-diaminopimelic acid. The DNA G+C content was 67.0 mol%. Based on a polyphasic taxonomic characterization, strain CB-286315 T represents a novel genus and species, Longimicrobium terrae gen. nov., sp. nov., within the phylum Gemmatimonadetes. The type strain of Longimicrobium terrae is strain CB-286315 T ( 5 DSM 29007 T 5 CECT 8660 T ). In order to classify the novel taxon within the existing taxonomic framework, the family Longimicrobiaceae fam. nov., order Longimicrobiales ord. nov. and class Longimicrobia classis nov. are also proposed.The phylum Gemmatimonadetes is a cosmopolitan bacterial taxon, members of which inhabit a wide variety of ecological niches (DeBruyn et al., 2011;Hanada & Sekiguchi, 2014;Zhang et al., 2003) including terrestrial and marine environments (Kamagata, 2010). Although they are found worldwide, members of the phylum are usually found at low frequency in soil microbial communities, with relative abundances ranging from 0.2 to 6.5 % (DeBruyn et al., 2011). Presently, .13 000 environmental 16S rRNA gene sequences available in the SILVA SSU Ref 123 database are likely to be associated with the phylum Gemmatimonadetes (Quast et al., 2013). According to the environmental 16S rRNA gene sequences, the phylum Gemmatimonadetes can be divided into five major lineages at the class level (groups 1-5) (Hanada & Sekiguchi, 2014). Group ...

Little is known of the bacterial communities associated with the rhizosphere of wild plant species found in natural settings. The rhizosphere bacterial community associated with wild thyme, Thymus zygis L., plants was analyzed using cultivation, the creation of a near-full length 16S rRNA gene clone library and 454 amplicon pyrosequencing. The bacterial community was dominated by Proteobacteria (mostly Alphaproteobacteria and Betaproteobacteria), Actinobacteria, Acidobacteria, and Gemmatimonadetes. Although each approach gave a different perspective of the bacterial community, all classes/subclasses detected in the clone library and the cultured bacteria could be found in the pyrosequencing datasets. However, an exception caused by inconclusive taxonomic identification as a consequence of the short read length of pyrotags together with the detection of singleton sequences which corresponded to bacterial strains cultivated from the same sample highlight limitations and considerations which should be taken into account when analysing and interpreting amplicon datasets. Amplicon pyrosequencing of replicate rhizosphere soil samples taken a year later permit the definition of the core microbiome associated with Thymus zygis plants. Abundant bacterial families and predicted functional profiles of the core microbiome suggest that the main drivers of the bacterial community in the Thymus zygis rhizosphere are related to the nutrients originating from the plant root and to their participation in biogeochemical cycles thereby creating an intricate relationship with this aromatic plant to allow for a feedback ecological benefit.