Regulation of the KstR2 regulon of Mycobacterium tuberculosis by a cholesterol catabolite

Cholesterol catabolism is widespread in actinobacteria and is critical for Mycobacterium tuberculosis (Mtb) virulence. Catabolism of steroid nucleus rings C and D is poorly understood: it is initiated by the CoA thioesterification of 3aα‐H‐4α(3′‐propanoate)‐7aβ‐methylhexahydro‐1,5‐indanedione (HIP) by FadD3, whose gene is part of the KstR2 regulon. In Mtb, genes of this regulon were upregulated up to 30‐ and 22‐fold during growth on cholesterol and HIP, respectively, versus another minimal medium. In contrast, genes involved in degrading the cholesterol side‐chain and nucleus rings A and B were only upregulated during growth on cholesterol. Similar results were obtained in Rhodococcus jostii RHA1. Moreover, the regulon was not upregulated in a ΔfadD3 mutant unable to produce HIP‐CoA. In electrophoretic mobility shift assays, HIP‐CoA relieved the binding of KstR2_Mtb to each of three KstR2 boxes: CoASH, HIP and a related CoA thioester did not. Inspection of the structure of KstR2_RHA1 revealed no obvious HIP‐CoA binding pocket. The results establish that Mtb can catabolize the entire cholesterol molecule and that HIP‐CoA is an effector of KstR2. They further indicate that KstR2 specifically represses the expression of the HIP degradation genes in actinobacteria, which encode a lower pathway involved in the catabolism of multiple steroids.     

FadD3 is an acyl‐CoA synthetase that initiates catabolism of cholesterol rings C and D in actinobacteria

The cholesterol catabolic pathway occurs in most mycolic acid‐containing actinobacteria, such as Rhodococcus jostii RHA1, and is critical for Mycobacterium tuberculosis (Mtb) during infection. FadD3 is one of four predicted acyl‐CoA synthetases potentially involved in cholesterol catabolism. A ΔfadD3 mutant of RHA1 grew on cholesterol to half the yield of wild‐type and accumulated 3aα‐H‐4α(3′‐propanoate)‐7aβ‐methylhexahydro‐1,5‐indanedione (HIP), consistent with the catabolism of half the steroid molecule. This phenotype was rescued by fadD3 of Mtb. Moreover, RHA1 but not ΔfadD3 grew on HIP. Purified FadD3_Mtb catalysed the ATP‐dependent CoA thioesterification of HIP and its hydroxylated analogues, 5α‐OH HIP and 1β‐OH HIP. The apparent specificity constant (k_cat/K_m) of FadD3_Mtb for HIP was 7.3 ± 0.3 × 10⁵ M^?1 s^?1, 165 times higher than for 5α‐OH HIP, while the apparent K_m for CoASH was 110 ± 10 μM. In contrast to enzymes involved in the catabolism of rings A and B, FadD3_Mtb did not detectably transform a metabolite with a partially degraded C17 side‐chain. Overall, these results indicate that FadD3 is a HIP‐CoA synthetase that initiates catabolism of steroid rings C and D after side‐chain degradation is complete. These findings are consistent with the actinobacterial kstR2 regulon encoding ring C/D degradation enzymes.     

Induction of vitellogenin synthesis in an Atlantic salmon (Salmo salar) hepatocyte culture: a sensitive in vitro bioassay for the oestrogenic and anti-oestrogenic activity of chemicals

A variety of organic compounds have been documented to bind to the oestrogen receptor and induce oestrogenic effects in different vertebrates. The presence of these environmental oestrogens or oestrogen mimics in the aquatic environment has been suspected of disrupting the normal endocrinology of wild populations of fish. In this study, induction of vitellogenin synthesis in primary hepatocytes from Atlantic salmon (Salmo salar) was optimized and validated as an oestrogenic in vitro bioassay using a sensitive capture vitellogenin enzyme-linked immunosorbent assay. After proper optimization (cell media supplements, cell density, temperature and exposure time), this assay gave a sensitive and reproducible response to both endogenous steroids (relative potency: 17β-oestradiol?oestriol>oestrone>17α-oestradiol) and a range of common oestrogen mimics (relative potency: ethynyloestradiol and diethylstilboestrol?genistein and zearalenone?bisphenol A and 4-t-octylphenol>4-n-nonylphenol and 2′-chloro,4-chloro-diphenyltrichloroethane (o,p′-DDT). However, the androgen testosterone and the putative oestrogen mimics dieldrin and toxaphene were not shown to be oestrogenic using this hepatocyte bioassay. Oestrogen-induced vitellogenin synthesis was efficiently inhibited by the anti-oestrogen ZM 189.154, suggesting that this bioassay may be used for testing both the oestrogenic and the anti-oestrogenic properties of chemicals.     

Oestrogenic activity of CPRG (chlorophenol red-β-D-galactopyranoside), a β-galactosidase substrate commonly used in recombinant yeast oestrogenic assays

The finding that a variety of chemicals display oestrogenic activity has resulted in the development of in vitro and in vivo assays to assess oestrogenic activity. One such assay, the yeast oestrogen assay (YES) makes use of recombinant yeast cells that harbour an oestrogen receptor expression cassette and a reporter construct, coding for bgalactosidase. The induction mechanism starts with the binding of oestrogenic compounds to the oestrogen receptor. This complex activates the production of β-galactosidase. The β-galactosidase activity is thus a measure of the oestrogenic activity of chemical compounds. In the YES assay, the β-galactosidase activity may be quantified with the chromogenic substrate chlorophenol red-β-d-galactopyranoside (CPRG). In the present study it is reported that CPRG or its β-galactosidase degradation product chlorophenol red act in the YES as an oestrogenic compound itself. The implications of this finding are described. It is especially argued that chlorophenol red production after prolonged incubation of the assay might be misinterpreted as an oestrogenic effect of the test compound.     

Diversity of Cultivated and Uncultivated Actinobacterial Endophytes in the Stems and Roots of Rice

A dual approach consisting of cultivation and molecular retrieval of actinobacterial 16S rRNA genes was used to characterize the diversity of actinobacterial community inhabiting interior of rice stems and roots. Streptomyces is the most frequently isolated genus from rice stems and roots. Forty-five clones chosen randomly among 250 clones in the 16S rRNA gene clone library from roots were affiliated with nine genera of actinobacteria and uncultured actinobacteria (Mycobacterium, Streptomyces, Micromonospora, Actinoplanes, Frankia, Dactylosporangium, Amycolatopsis, Corynebacterium, Rhodococcus, and uncultured actinobacterium). However, 33 clones from stems were affiliated with four genera and uncultured actinobacteria (Streptomyces, Mycobacterium, Nocardiodies, Janibacter, uncultured earthworm cast bacterium, uncultured earthworm intestine bacterium, and uncultured actinobacterium). Species similar to S. cyaneus were isolated from surface-sterilized roots and stems of rice and detected inside rice roots by culture-independent methods. Species similar to S. caviscabies, S. scabies, and S. turgidiscabies were simultaneously detected from the interior of rice stems by the culture-dependent and culture-independent methods. S. galilaeus was detected from the interior of rice stems and roots. These results indicated that some actinobacterial populations in rice stems were correlated with those in roots. Tian and Cao contributed equally to this work     

贵州兴义喀斯特洞穴可培养放线菌多样性及抗菌活性初筛

【目的】进一步了解兴义喀斯特洞穴可培养放线菌资源及产活性代谢产物的能力。【方法】选取多种分离培养基,利用稀释直接涂布平板法对贵州黔西南兴义市多个喀斯特洞穴的土壤和岩石进行可培养放线菌资源分离;利用三种发酵培养基对相关放线菌进行生物产物初筛。【结果】根据16S rRNA基因序列的比对分析,将分离得到的251株放线菌分别归类到44个属,其中链霉菌属(Streptomyces)占分离菌株的比例为24.30%,小单孢菌属(Micromonospora)占比11.95%,红球菌属(Rhodococcus)占比9.16%,微杆菌属(Microbacterium)占比7.17%,诺卡氏菌属(Nocardia)占比6.37%,该五类放线菌为该地区可培养放线菌的优势菌群。对70株细菌进行活性次级代谢产物筛选,其中35株放线菌对指示菌具有抑制活性,且主要类群为链霉菌属和小单孢菌属。【结论】贵州兴义喀斯特洞穴中存在丰富多样的放线菌类群,且蕴藏大量具有产生活性次级代谢产物能力的菌株,为医药产业提供潜力菌株资源,极具进一步发掘和研究的价值。     

A comparative study on the phylogenetic diversity of culturable actinobacteria isolated from five marine sponge species

A cultivation-based approach was employed to compare the culturable actinobacterial diversity associated with five marine sponge species (Craniella australiensis, Halichondria rugosa, Reniochalina sp., Sponge sp., and Stelletta tenuis). The phylogenetic affiliation of the actinobacterial isolates was assessed by 16S rDNA-RFLP analysis. A total of 181 actinobacterial strains were isolated using five different culture media (denoted as M1–M5). The type of medium exhibited significant effects on the number of actinobacteria recovered, with the highest number of isolates on M3 (63 isolates) and the lowest on M1 (12 isolates). The genera isolated were also different, with the recovery of three genera on M2 and M3, and only a single genus on M1. The number of actinobacteria isolated from the five sponge species was significantly different, with a count of 83, 36, 30, 17, and 15 isolates from S. tenuis, H. rugosa, Sponge sp., Reniochalina sp., and C. australiensis, respectively. M3 was the best isolation medium for recovery of actinobacteria from S. tenuis, H. rugosa, and Sponge sp., while no specific medium preference was observed for the recovery of actinobacteria from Reniochalina sp., and C. australiensis. The RFLP fingerprinting of 16S rDNA genes digested with HhaI revealed six different patterns, in which 16 representative 16S rDNAs were fully sequenced. Phylogenetic analysis indicated that 12 strains belong to the group Streptomyces, three strains belong to Pseudonocardia, and one strain belongs to Nocardia. Two strains C14 (from C. australiensis) and N13 (from Sponge sp.) have only 96.26% and 96.27% similarity to earlier published sequences, and are therefore potential candidates for new species. The highest diversity of three actinobacteria genera was obtained from Sponge sp., though the number of isolates was low. Two genera of actinobacteria, Streptomyces, and Pseudonocardia, were isolated from both S. tenuis and C. australiensis. Only the genus of Streptomyces was isolated from H. rugosa and Reniochalina sp. Sponge species have been demonstrated here to vary as sources of culturable actinobacterial diversity, and the methods for sampling such diversity presented may be useful for improved sampling of such diversity.     

Diversity of Actinobacterial community in saline sediments from Yunnan and Xinjiang, China

The diversity and community structures of actinobacteria in saline sediments collected from Yunnan and Xinjiang Provinces, China, were investigated with cultivation and 16S rRNA gene analysis. A total of 163 actinobacterial isolates were obtained, and they were affiliated with the order Actinomycetales (distributed into five suborders: Streptosporangineae, Micrococcineae, Streptomycineae, Pseudonocardineae, and Glycomycineae). A total of 748 actinobacterial 16S rRNA gene clones were examined, and they could be classified into Actinomycetales, Acidimicrobiales, and unclassified actinobacteria. The Actinomycetales sequences were distributed into nine suborders: Streptosporangineae, Glycomycineae, Micromonosporineae, Pseudonocardineae, Corynebacterineae, Frankineae, Propionibacterineae, Streptomycineae, and Micrococcineae. The unclassified actinobacteria contained three new clusters at the level of subclass or order. Our 16S rRNA gene phylogenetic data indicated that actinobacterial communities were very diverse in the investigated saline sediments (salinity 0.4–11.6%) and some actinobacterial members may be halotolerant or halophilic. The actinobacterial community structures in the saline sediments were different from those in marine and freshwater environments. Our data have implications for a better understanding of the distribution of Actinobacteria in saline environments. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

青藏高原阿里、那曲和海西地区土壤可培养放线菌的多样性

【目的】为了研究青藏高原北部地区土壤可培养放线菌的多样性,并比较不同选择性分离培养基对高原土壤放线菌的分离效果。【方法】使用9种分离培养基,并尝试添加藤黄微球菌发酵液,对采集自阿里、那曲和海西地区的14份土壤样品中的放线菌进行选择性分离。通过16S r RNA基因序列分析对分离菌株进行初步分类鉴定,并在不同分类水平上统计所分离得到的放线菌多样性。【结果】分离得到去重复后的放线菌255株,分布于放线菌门的8个目,14个科,23个属,包含94个可能的物种。其中至少25个物种可能为新种,分布于13个属。链霉菌属的菌株108株,可能的物种28个,是最主要的优势菌属。分离培养基中添加藤黄微球菌发酵液明显增加了放线菌分离菌株的数量和多样性,稀释的葡萄糖酵母麦芽汁培养基适合分离链霉菌,淀粉甘油脯氨酸培养基、丙酸钠酪蛋白培养基等则适合分离稀有放线菌。【结论】青藏高原北部土壤放线菌多样性非常丰富,并且存在较多的新颖放线菌类群;添加藤黄微球菌发酵液是提高放线菌分离效率的有效手段。     

Topical KGF treatment as a therapeutic strategy for vaginal atrophy in a model of ovariectomized mice

One of the most frequent complaints for post‐menopausal women is vaginal atrophy, because of reduction in circulating oestrogens. Treatments based on local oestrogen administration have been questioned as topic oestrogens can reach the bloodstream, thus leading to consider their safety as controversial, especially for patients with a history of breast or endometrial cancers. Recently, growth factors have been shown to interact with the oestrogen pathway, but the mechanisms still need to be fully clarified. In this study, we investigated the effect of keratinocyte growth factor (KGF), a known mitogen for epithelial cells, on human vaginal mucosa cells, and its potential crosstalk with oestrogen pathways. We also tested the in vivo efficacy of KGF local administration on vaginal atrophy in a murine model. We demonstrated that KGF is able to induce proliferation of vaginal mucosa, and we gained insight on its mechanism of action by highlighting its contribution to switch ERα signalling towards non‐genomic pathway. Moreover, we demonstrated that KGF restores vaginal trophism in vivo similarly to intravaginal oestrogenic preparations, without systemic effects. Therefore, we suggest a possible alternative therapy for vaginal atrophy devoid of the risks related to oestrogen‐based treatments, and a patent (no. RM2012A000404) has been applied for this study.     

Ruminant feces harbor diverse uncultured symbiotic actinobacteria

To isolate actinobacteria from ruminant feces and elucidate their correlations with ruminants, the actinobacterial community in sheep (Ovis aries) and cattle (Bos taurus) feces was determined by cultivation and clone library methods. Most of actinobacteria isolated belonged to Streptomyces, Amycolatopsis, Micromonospora, and Cellulosimicrobium genera. The strains showed above 99 % similarity with the type strains, respectively. All the strains isolated could grow on media containing pectin, cellulose, or xylan as the sole carbon sources. However, most antibacterial and antifungal activities were found in Streptomyces species. Clone library analysis revealed that the genera Mycobacterium, Aeromicrobium, Rhodococcus, Cellulomonas were present in cattle and sheep feces. In contrast, the 16S rRNA genes showed less than 98 % similarity with the type strains. The analysis of actinobacterial community in ruminant feces by clone library and cultivation yielded a total of 10 actinobacterial genera and three uncultured actinobacterial taxa. The ruminant feces harbored diverse actinobacterial community. Ruminants may represent an underexplored reservoir of novel actinomycetes of potential interest for probiotics and drug discovery.     

Gene delivery to pancreatic exocrine cells in vivo and in vitro

Background

Oestrogenic contaminants are widespread in the aquatic environment and have been shown to induce adverse effects in both wildlife (most notably in fish) and humans, raising international concern. Available detecting and testing systems are limited in their capacity to elucidate oestrogen signalling pathways and physiological impacts. Here we developed a transient expression assay to investigate the effects of oestrogenic chemicals in fish early life stages and to identify target organs for oestrogenic effects. To enhance the response sensitivity to oestrogen, we adopted the use of multiple tandem oestrogen responsive elements (EREc38) in a Tol2 transposon mediated Gal4ff-UAS system. The plasmid constructed (pTol2_ERE-TATA-Gal4ff), contains three copies of oestrogen response elements (3ERE) that on exposure to oestrogen induces expression of Gal4ff which this in turn binds Gal4-responsive Upstream Activated Sequence (UAS) elements, driving the expression of a second reporter gene, EGFP (Enhanced Green Fluorescent Protein).

Results

The response of our construct to oestrogen exposure in zebrafish embryos was examined using a transient expression assay. The two plasmids were injected into 1?C2 cell staged zebrafish embryos, and the embryos were exposed to various oestrogens including the natural steroid oestrogen 17?-oestradiol (E₂), the synthetic oestrogen 17??- ethinyloestradiol (EE₂), and the relatively weak environmental oestrogen nonylphenol (NP), and GFP expression was examined in the subsequent embryos using fluorescent microscopy. There was no GFP expression detected in unexposed embryos, but specific and mosaic expression of GFP was detected in the liver, heart, somite muscle and some other tissue cells for exposures to steroid oestrogen treatments (EE₂; 10?ng/L, E₂; 100?ng/L, after 72?h exposures). For the NP exposures, GFP expression was observed at 10???g NP/L after 72?h (100???g NP/L was toxic to the fish). We also demonstrate that our construct works in medaka, another model fish test species, suggesting the transient assay is applicable for testing oestrogenic chemicals in fish generally.

Conclusion

Our results indicate that the transient expression assay system can be used as a rapid integrated testing system for environmental oestrogens and to detect the oestrogenic target sites in developing fish embryos.     

C/N Ratio Drives Soil Actinobacterial Cellobiohydrolase Gene Diversity

Cellulose accounts for approximately half of photosynthesis-fixed carbon; however, the ecology of its degradation in soil is still relatively poorly understood. The role of actinobacteria in cellulose degradation has not been extensively investigated despite their abundance in soil and known cellulose degradation capability. Here, the diversity and abundance of the actinobacterial glycoside hydrolase family 48 (cellobiohydrolase) gene in soils from three paired pasture-woodland sites were determined by using terminal restriction fragment length polymorphism (T-RFLP) analysis and clone libraries with gene-specific primers. For comparison, the diversity and abundance of general bacteria and fungi were also assessed. Phylogenetic analysis of the nucleotide sequences of 80 clones revealed significant new diversity of actinobacterial GH48 genes, and analysis of translated protein sequences showed that these enzymes are likely to represent functional cellobiohydrolases. The soil C/N ratio was the primary environmental driver of GH48 community compositions across sites and land uses, demonstrating the importance of substrate quality in their ecology. Furthermore, mid-infrared (MIR) spectrometry-predicted humic organic carbon was distinctly more important to GH48 diversity than to total bacterial and fungal diversity. This suggests a link between the actinobacterial GH48 community and soil organic carbon dynamics and highlights the potential importance of actinobacteria in the terrestrial carbon cycle.     

Evolution of oestrogen functions in vertebrates

Steroidal oestrogens have been isolated from marine and terrestrial animals representative of all major classes of vertebrates including fish, amphibians, reptiles, birds and mammals. In general, oestrogens are responsible for most features characteristic of the female sex of a species, such as metabolic, behavioural and morphological changes during the stages of reproduction; they also support several processes in males. The evolution of the hormonal system always involves both the ligand and its sites of interaction. In the case of oestrogens, the steroid producing enzymes, mainly the aromatase complex, and the oestrogen receptor belong together within their co-evolution. The finding of oestrogenic steroids, the more recent identification of aromatase and receptor genes and their expression fit together, thereby confirming the importance for all vertebrates. Within the present paper, the evolution of the physiological functions of oestrogens from oviparous vertebrates to Eutherian mammals, oestrogen biosynthesis, metabolization and signalling pathways will be reviewed in detail.     

Glucocorticoids suppress and oestrogens enhance the lipopolysaccharide-induced increase in putrescine and N-acetylspermidine in mouse liver

Previously we reported that administration of lipopolysaccharide (LPS) to mice increased the hepatic levels of putrescine (PUT) and N¹-acetylspermidine (N¹-acetyl-SPD). In the current study, we examined the in vivo effects of some steroid hormones on the LPS-induced increase in PUT and N¹-acetyl-SPD. Corticosterone, hydrocortisone and dexamethasone suppressed the LPS-induced increase in PUT and N¹-acetyl-SPD in mouse liver in a dose-dependent manner, dexamethasone being the most effective among them. On the other hand, oesterone and oestradiol-17β enhanced the LPS-induced increase in PUT and N¹-acetyl-SPD in a dose-dependent manner. Oestradiol-17α and 16β-ethyl-oestradiol, as an inactive oestradiol isomer and an antioestrogen, respectively, likewise enhanced the increase in PUT and N¹-acetyl-SPD concentrations induced by LPS. 16α-hydroxy-oestradiol (oestriol), 16α-hydroxyestrone, 2-hydroxyoestradiol, 2-hydroxyoestrone, progesterone, testosterone, diethylstilboestrol and nonsteroidal antioestrogen such as tamoxifen and nafoxidine had no effect on the increase. Oestradiol-17β enhanced and corticosterone had little on the carbon tetrachloride-induced increase in PUT and N¹-acetyl-SPD. These results suggest that glucocorticoids suppress the increase by preventing the immunological injury by Kupffer cells on hepatocytes and that the stimulatory effect of oestrogens may not be associated with their oestrogenic activities mediated by the oestrogen receptor system.     

Isolation,Classification and Antagonistic Properties of Alkalitolerant Actinobacteria from Algerian Saharan Soils

Abstract

The Sahara, one of the most extreme environments on Earth, constitutes an unexplored source of alkalitolerant actinobacteria. In this work, we studied the diversity of alkalitolerant actinobacteria in various soils collected from different regions of the Algerian Sahara. A total of 29 alkalitolerant actinobacterial strains were isolated by using a complex agar medium. The diversity of these actinobacteria was evaluated using a polyphasic approach, which included morphological, chemotaxonomic, physiological (numerical taxonomy) and 16S rRNA gene analyses. The isolates which were assigned to the genus Nocardiopsis, shared relatively low 16S rRNA gene sequences similarities compared to closely related species suggesting that they belonged to putatively new species. All of the strains were tested for antibiotic activity against a broad range of microorganisms and screened for genes encoding polyketide synthases and non-ribosomal peptide synthetases and found to have the potential to produce secondary metabolites. Consequently, the study supports the view that extreme environments contain many novel actinobacteria, which represent an unexplored source for the discovery of biologically active compounds.     

Illumina-Based Sequencing Analysis Directed Selection for Actinobacterial Probiotic Candidates for Banana Plants

As potential probiotic candidates, plant vertically transmitted actinobacteria are beneficial to growth and health of host plants. New methods to isolate the actinobacterial taxa with low growth rates should be developed. Based on the actinobacterial population information, the probiotic actinobacterial taxa could be directly isolated from healthy banana shoot tips. However, actinobacterial DNAs with high GC contents could bias estimates of actinobacteria by PCR. In the study, two amplicon sequencing strategies were adopted to elucidate the endophytic actinobacterial community of banana plants. More than 92.5% bacterial OTUs were affiliated with actinobacteria by these two strategies, and total 14,289 actinobacterial OTUs with above 97% similarity were detected in banana shoot tips. Although the libraries generated by the two strategies differed in the abundance of some genera, Mycobacterium and Nocardia dominated both libraries and most actinobacterial taxa were overlapped. Higher phylogenetic resolution actinobacteriome of banana plants was successfully established. Based on the endophytic actinobacterial community information, the streptomycetes were isolated from shoot tips. Pot experiments illustrated that the strain could promote banana plantlet growth and elevate resistance to Fusarium oxysporum f. sp. cubense (FOC) under FOC infested soils. The results suggested that the selection for probiotic agents based on actinobacteriome analysis is reliable and feasible compared with present greenhouse selection.     

Molecular Phylogeny and Diversity of the Salt-Tolerant Alkaliphilic Actinobacteria Inhabiting Coastal Gujarat,India

Actinobacteria is a dominant phylum in saline soil and play important roles in the process of organic matter decomposition and biogeochemical cycling. In this study, we investigated the diversity and phylogeny of the haloalkaliphilic actinobacteria that inhabited the saline soil of Coastal Gujarat (India) using conventional and molecular approaches. The actinobacteria were diversified on the basis of their growth patterns, morphology, spore color and sugar utilization. The cultivated actinobacteria were genetically diverse, with the ability to grow at high salt concentrations. The salt resistance feature was widely distributed among the isolates and not confined to any particular phylogenetic cluster. The PCR -DGGE approach was used to assess molecular diversity and to mitigate the limitation of the 16S rRNA sequence approach. Reproducible band profiles confirmed that the PCR-DGGE provided an excellent tool for the 16S rDNA heterogeneity analysis. The migration behavior of the 16S rRNA genes on the DGGE gel suggested lack of correlation between the band numbers and α-diversity. The findings highlighted the trends associated with the microbial community and signify the role of the DGGE in distinguishing a group of species that exhibit 16S rRNA based phylogenetic relatedness with distinct phenotypic characters. Based on the 16S rRNA genes, the actinobacteria were identified as belong to Nocardiopsis, Brachybacterium, Streptomyces and Prauseria. Nocardiopsis was the most predominant actinobacterial genera. The study indicated that a combination of the conventional and molecular approaches could be highly significant in analyzing the diversity of the actinobacteria from the saline habitat.     

Diversity of cultivable actinobacteria in geographically widespread marine sediments

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.