A taxonomic study was carried out to clarify the taxonomy of representatives of a group of marine actinomycetes previously designated MAR 1 and considered to belong to the family Micromonosporaceae. The organisms had phenotypic properties consistent with their assignment to this taxon. The strains formed a distinct taxon in the 16S rRNA Micromonosporaceae gene tree and shared a range of phenotypic properties that distinguished them from members of all of the genera with validly published names classified in this family. The name proposed for this novel taxon is Salinispora gen. nov. The genus contains two species recognized using a range of genotypic and phenotypic criteria, including comparative 16S–23S rRNA gene spacer region and DNA–DNA relatedness data. The names proposed for these taxa are Salinispora arenicola sp. nov., the type species, and Salinispora tropica sp. nov.; the type strains of these novel species have been deposited in service culture collections as strain CNH-643T (=ATCC BAA-917T=DSM 44819T) and strain CNB-440T (=ATCC BAA-916T=DSM 44818T), respectively.

In this study, we redesigned and evaluated primers for the class Actinobacteria. In silico testing showed that the primers had a perfect match with 82% of genera in the class Actinobacteria, representing a 26-213% improvement over previously reported primers. Only 4% of genera that displayed mismatches did so in the terminal three bases of the 3' end, which is most critical for polymerase chain reaction success. The primers, designated S-C-Act-0235-a-S-20 and S-C-Act-0878-a-A-19, amplified an approximately 640 bp stretch of the 16S rRNA gene from all actinobacteria tested (except Rubrobacter radiotolerans) up to an annealing temperature of 72 degrees C. An Actinobacteria Amplification Resource (http://microbe2.ncl.ac.uk/MMB/AAR.htm) was generated to provide a visual guide to aid the amplification of actinobacterial 16S rDNA. Application of the primers to DNA extracted from marine and terrestrial samples revealed the presence of actinobacteria that have not been described previously. The use of 16S rDNA similarity and DNA-DNA pairing correlations showed that almost every actinomycete clone represented either a new species or a novel genus. The results of this study reinforce the proposition that current culture-based techniques drastically underestimate the diversity of Actinobacteria in the environment and highlight the need to evaluate taxon-specific primers regularly in line with improvements in databases holding 16S rDNA sequences.

A screening method was established to detect inhibitors of the biosynthetic pathways of aromatic amino acids and para-aminobenzoic acid, the precursor of folic acid, using an agar A successful search for novel antibacterial metabolites has to meet three criteria, first, a specific target which is essential for the metabolism of a bacterium and not yet provided with an known inhibitor. Second, a set of taxonomically characterized and dereplicated microorganisms as producers of secondary metabolites, and last but not least a lucky but experienced hand for strain isolation and cultivation. We have chosen the shikimate pathway as an essential target of bacterial metabolism, with special consideration of the biosynthesis of aromatic amino acids and para-aminobenzoic (pAba) acid derived from the keymetabolite chorismate. Only a few antimetabolites are known as inhibitors of aromatic amino acids, such as L-2,5-dihydrophenylalanine2), an antagonist of phenlyalanine, and glyphosate that inhibits 3-enolpyruvylshikimate-3-phosphate synthase3,4). To our knowledge, no natural product inhibitor of pAba biosynthesis has been described in the literature. This pathway, which is catalyzed by two enzymes, 4-amino-4-deoxychorismic acid (ADC) synthase and ADC lyase, seems to be of considerable interest for the development of novel antibiotics since it is directly linked to folic acid biosynthesis, which is established in plants, fungi, prokaryotes and parasites of the apicomplexa group (Plasmodium, Toxoplasma) but not in vertebrates.As suitable producers of bioactive metabolites we screened within the order Actinomycetales terrestrial and marine members of the families Streptomycetaceae and Micromonosporaceae and rare actinomycete genera. A total of 930 extracts derived from 201 actinomycetes were subjected to the screening. Among them, only AB-18-032, an extract from a marine isolate from a sediment collected from the Sea of Japan, was found to exhibit activity against

Bacterial diversity in a deep-sea sediment was investigated by constructing actinobacterium-specific 16S ribosomal DNA (rDNA) clone libraries from sediment sections taken 5 to 12, 15 to 18, and 43 to 46 cm below the sea floor at a depth of 3,814 m. Clones were placed into operational taxonomic unit (OTU) groups with >99% 16S rDNA sequence similarity; the cutoff value for an OTU was derived by comparing 16S rRNA homology with DNA-DNA reassociation values for members of the class Actinobacteria. Deep-sea sediments cover 63.5% of the Earth's surface (12) and represent the most undersampled marine habitat (5). Deep-sea sediments, once thought of as uniform featureless environments, are extremely heterogeneous; recent reports suggest that species diversity in deep-sea sediments is greater than in coastal sediments (16,26) and may even rival that of tropical rainforests (38). To date, few studies have focused on microbial diversity in nonhydrothermal vent system deep seas (8,18,21,23,27,57), and fewer have investigated diversity through depth profiles (21, 57). Furthermore, all microbial diversity investigations made using marine sediments represent surveys of microbial diversity; none have attempted to estimate and compare bacterial diversity at different sites.

Reports describing actinobacteria isolated from marine environments have been dominated by Micromonospora, Rhodococcus and Streptomyces species. Recent culture-independent studies have shown that marine environments contain a high diversity of actinobacterial species that are rarely, if at all, recovered by cultivation-based methods. In this study, it is shown that cultivation-independent methods can be used to guide the application of selective isolation methods. The detection of marine-derived actinobacterial species that have previously only been reported from terrestrial habitats is highlighted. This study provides good evidence that the previously described low diversity of actinobacterial species isolated from marine environments does not reflect an actual low species diversity, and that the use of informed selective isolation procedures can aid in the isolation of members of novel taxa.