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.

/pdf/genome-based-taxonomic-classification-of-the-phylum-4uc1zrzg88.pdf

Genome-Based Taxonomic Classification of the Phylum Actinobacteria

Marine actinomycetes: an ongoing source of novel bioactive metabolites.

New structurally diverse natural products are discovered when novel screening procedures are introduced or when high quality biological materials from new sources are examined in existing screens, hence it is important to foster these two aspects of novelty in drug discovery programmes. Amongst prokaryotes, actinomycetes, notably streptomycetes, remain a rich source of new natural products though it has become increasingly difficult to find such metabolites from common actinomycetes as screening ‘old friends’ leads to the costly rediscovery of known compounds. The bioprospecting strategy which is the subject of this review is based upon the premise that new secondary metabolites can be found by screening relatively small numbers of dereplicated, novel actinomycetes isolated from marine sediments. The success of the strategy is exemplified by the discovery of a range of novel bioactive compounds, notably atrop-abyssomicin C and proximicins A, B and C from Verrucosispora strains isolated from sediment samples taken from the Sea of Japan and the Raune Fjord, respectively, and the dermacozines derived from Dermacoccus strains isolated from the Challenger Deep of the Mariana Trench in the Pacific Ocean. The importance of current advances in prokaryotic systematics in work of this nature is stressed and a plea made that resources be sought to train, support and employ the next generation of actinobacterial systematists.

A guide to successful bioprospecting: Informed by actinobacterial systematics

Rare Actinomycetes from underexplored marine environments are targeted in drug discovery studies due to the Actinomycetes’ potentially huge resource of structurally diverse natural products with unusual biological activity. Of all marine bacteria, 10 % are Actinomycetes, which have proven an outstanding and fascinating resource for new and potent bioactive molecules. Past and present efforts in the isolation of rare Actinomycetes from underexplored diverse natural habitats have resulted in the isolation of about 220 rare Actinomycete genera of which more than 50 taxa have been reported to be the producers of 2,500 bioactive compounds. That amount represents greater than 25 % of the total Actinomycetes metabolites, demonstrating that selective isolation methods are being developed and extensively applied. Due to the high rediscovery rate of known compounds from Actinomycetes, a renewed interest in the development of new antimicrobial agents from rare and novel Actinomycetes is urgently required to combat the increasing number of multidrug-resistant human pathogens. To facilitate that discovery, this review updates all selective isolation media including pretreatment and enrichment methods for the isolation of marine rare Actinomycetes. In addition, this review demonstrates that discovering new compounds with novel scaffolds can be increased by intensive efforts in isolating and screening rare marine genera of Actinomycetes. Between 2007 and mid-2013, 80 new rare Actinomycete species were reported from marine habitats. They belong to 23 rare families, of which three are novel, and 20 novel genera. Of them, the family Micromonosporaceae is dominant as a producer of promising chemical diversity.

/pdf/culturable-rare-actinomycetes-diversity-isolation-and-marine-45x6rpj2tv.pdf

Culturable rare Actinomycetes: diversity, isolation and marine natural product discovery.

Piper nigrum is an interesting plant to study the endophytic microbial factors affecting plant growth because of its unique features. Endophytic bacterial isolation from the plant resulted in the isolation of twelve bacterial isolates which were screened for various plant growth promoting properties like phosphate solubilization, ACC deaminase production, siderophore production etc. Interestingly, seven isolates were found to have IAA biosynthetic potential. Bacterial isolates with multiple plant growth promoting properties were studied for their growth promoting effect on Vigna radiata seedlings. This resulted in the identification of Klebsiella sp. (PnB 10) and Enterobacter sp. (PnB 11) as the isolates with excellent growth promoting properties. The results confirm promising applications of the endophytic bacterial isolates obtained in the study and also their possible growth promoting effect in P. nigrum.

Plant growth promoting potential of endophytic bacteria isolated from Piper nigrum

The taxonomic position of an actinomycete, designated SCSIO 00231(T), isolated from a sediment sample collected from the northern South China Sea, was determined by using a polyphasic approach. The organism formed fragmented substrate hyphae and sparse aerial mycelium on modified ISP 2 medium. Phylogenetic analysis based on the 16S rRNA gene sequence showed that strain SCSIO 00231(T) fell into the family Pseudonocardiaceae, in which it formed a distinct lineage and was loosely associated with Thermocrispum municipale DSM 44069(T), with 93% similarity. The other closest phylogenetic neighbours were Saccharopolyspora erythraea NRRL 2338(T) (92.6% similarity) and Amycolatopsis sacchari DSM 44468 (T) (93.1% similarity). The isolate had cell-wall type IV (meso-diaminopimelic acid and whole-cell sugars arabinose, galactose and glucose) and phospholipid type Ill. The predominant menaquinone was MK-9(H-4)The G + C content of the genomic DNA was 69 mol%. Based on these data, strain SCSIO 00231(T) can be readily distinguished from previously described organisms and represents a new genus within the family Pseudonocardiaceae. The name Sciscionella gen. nov. is proposed, with the novel species Sciscionella marina sp. nov. The type strain of Sciscionella marina is SCSIO 00231(T) (=KCTC 19433(T) =CCTCC AA208009(T)).

/pdf/sciscionella-marina-gen-nov-sp-nov-a-marine-actinomycete-4b9897fnum.pdf

Sciscionella marina gen. nov., sp. nov., a marine actinomycete isolated from a sediment in the northern South China Sea

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Sciscionella marina gen. nov., sp. nov., a marine actinomycete isolated from a sediment in the northern South China Sea