Research on marine actinobacteria in India

Marine actinobacteriology is one of the major emerging areas of research in tropics. Marine actinobacteria occur on the sediments and in water and also other biomass (mangrove) and substrates (animal). These organisms are gaining importance not only for their taxonomic and ecological perspectives, but also for their unique metabolites and enzymes. Many earlier studies on these organisms were confined only to the temperate regions. In tropical environment, investigations on them have gained importance only in the last two decades. So far, from the Indian peninsula, 41 species of actinobacteria belonging to 8 genera have been recorded. The genus, Streptomyces of marine origin has been more frequently recorded. Of 9 maritime states of India, only 4 have been extensively covered for the study of marine actinobacteria. Most of the studies conducted pertain to isolation, identification and maintenance of these organisms in different culture media. Further, attention has been focused on studying their antagonistic properties against different pathogens. Their biotechnological potentials are yet to be fully explored.     

嗜盐放线菌资源及次生代谢产物研究进展

嗜盐放线菌是重要的极端微生物资源,因其独特的生长环境、生理机制而备受关注。本文对嗜盐放线菌的定义、生物多样性及次生代谢产物的研究进展进行综述。结合我国嗜盐放线菌的研究现状,分析尚存在的问题及其发展前景。     

Screening of marine actinobacteria for amylase enzymes inhibitors

Amylase inhibitor producing actinobacteria were isolated and characterized from terrestrial environment and there is no much report found from marine environment, hence in the present study, 17 strains isolated from the rhizosphere sediments of mangroves were tested for their amylase inhibition ability. Seawater requirement test for the growth of actinobacteria found that the strains SSR-3, SSR-12 and SSR-16 requires at least 50% and SSR-6 requires at least 25% seawater for their growth. The inhibition activity of both prokaryotic and eukaryotic amylase was tested by using Bacillus subtilis and Aspergillus niger. The maximum amylase activity (40mm) produced by the A. niger was taken as positive control, when the test actinobacteria strains grown in the medium they inhibited amylase activity and was evidenced by the reduction in inhibition zone (14–37 mm) similarly the amylase produced by the Bacillus subtilis was also recorded maximum (35 mm) amylase activity and was taken as positive control, and the test atinobacterial strains reduced enzyme action(12–33 mm) it varied levals. This indicates that the actinobacteria strains were controlled amylase enzyme activity in both the cases. The strain SSR-10 was highly effective and SSR-8 was less effective in inhibiting eukaryotic amylase produced by A. niger. The strain SSR-2 was effective and SSR-6 showed very less effect in inhibiting the prokaryotic amylase produced by the B subtilis.     

Mining novel biosynthetic machineries of secondary metabolites from actinobacteria

ABSTRACT

Secondary metabolites produced by actinobacteria have diverse structures and important biological activities, making them a useful source of drug development. Diversity of the secondary metabolites indicates that the actinobacteria exploit various chemical reactions to construct a structural diversity. Thus, studying the biosynthetic machinery of these metabolites should result in discovery of various enzymes catalyzing interesting and useful reactions. This review summarizes our recent studies on the biosynthesis of secondary metabolites from actinobacteria, including the biosynthesis of nonproteinogenic amino acids used as building blocks of nonribosomal peptides, the type II polyketide synthase catalyzing polyene scaffold, the nitrous acid biosynthetic pathway involved in secondary metabolite biosynthesis and unique cytochrome P450 catalyzing nitrene transfer. These findings expand the knowledge of secondary metabolite biosynthesis machinery and provide useful tools for future bioengineering.     

Pharmaceutically active secondary metabolites of microorganisms

The antibiotics have been useful in our battles against infectious bacteria and fungi for over 50 years. However, many antibiotics are used commercially, or are potentially useful, in medicine for activities other than their antibiotic action. They are used as antitumor agents, immunosuppressive agents, hypocholesterolemic agents, enzyme inhibitors, antimigraine agents, and antiparasitic agents. A number of these products were first discovered as antibiotics which failed in their development as such, or as mycotoxins. In addition to the above alternative applications, new powerful antibiotics have been discovered and commercialized in recent years and others are in clinical testing at the moment. A few successful secondary metabolites appear to have no antibiotic activity. The recently increased development of resistance to older antibacterial and antifungal drugs is being met with the use or clinical testing of older, underutilized or previously nondeveloped narrow-spectrum antibacterial products as well as powerful semisynthetic antifungal agents. Received: 28 December 1998 / Received revision: 26 April 1999 / Accepted: 1 May 1999     

Biologically active metabolites of marine actinobacteria

Data on the chemical structures and biologic activities of metabolites of obligate and facultative marine actinobacteria published between 2000 and 2007 are reviewed. The structural features of five groups of metabolites related to macrolides and compounds containing lactone, quinone, and diketopiperazine residues; cyclic peptides; alkaloids; and compounds of combined nature are discussed. The review shows the large chemical diversity of metabolites of actinobacteria isolated from marine ecotopes. In addition to metabolites identical to those previously isolated from terrestrial actinobacteria, marine actinobacteria produce compounds not found in other natural sources, including microorganisms. Probably, the biosynthesis of new chemotypes of bioactive compounds by marine actinobacteria is related to the chemical adaptation of microorganisms to the marine environment. The review emphasizes the importance of chemical studies of metabolites produced by marine actinobacteria. These studies will provide new data on marine microbial producers of biologically active compounds and the chemical structures and biologic activities of new natural lowmolecular-weight bioregulators.     

Antioxidant metabolites from marine alga-derived fungus Aspergillus wentii EN-48

Eight secondary metabolites (1–8) including a new seco-anthraquinone (wentiquinone C, 1) and a new benzamide derivative (methyl 4-(3,4-dihydroxybenzamido)butanoate, 2), as well as three other derivatives (4, 7, and 8) that were isolated from natural source for the first time, were characterized from the EtOAc extracts of the marine alga-derived endophytic fungus Aspergillus wentii EN-48. The structures of the isolated compounds were elucidated on the basis of 1D and 2D NMR experiments. Each of the isolated compounds was evaluated for α,α-diphenyl-picrylhydrazyl (DPPH) radical scavenging activity, and some of them showed potent activities with IC₅₀ values ranging from 5.2 to 99.4 μg/mL, compared to the positive control, butylated hydroxytoluene (BHT), with an IC₅₀ of 36.9 μg/mL.     

Unexpected applications of secondary metabolites

Secondary metabolites have been found to have interesting applications over and above their well-known medical uses, e.g., as antimicrobials, etc. These alternative applications include antitumor, cholesterol-lowering, immunosuppressant, antiprotozoal, antihelminth, antiviral and anti-ageing activities. Polyene antibiotics, such as amphotericin B, are of use as antiprion agents, antitumor drugs and against leishmaniasis. Other microbial natural products that show antibiotic activity are used against cancer e.g., doxorubicin, neomycin, β-lactams, bleomycin and rapamycin. Macrolide antibiotics, such as erythromycin, clarithromycin and azithromycin, improve pulmonary function in patients suffering from panbion cholitis. Pigments like prodigiosin and shikonin have antitumor activity, while violacein has anti-ulcer and antitumor activity and also acts as an antiprotozoal agent. Statins, in addition to lowering cholesterol and LDL levels, also decrease elevated C-reactive protein (CRP) levels independent of their cholesterol effects. Immunosppressants have many alternative effects: (i) Cyclosporin is proving useful in treatment of inflammatory disease such as asthma and muscular dystrophy. (ii) Rapamycin is extremely useful in preventing restenosis of stents grafted in balloon angioplasty. (iii) Tacrolimus and ascomycin help in treating inflammatory skin disease such as allergic contact dermatitis and psoriasis. Artemisinin, an antimalarial agent, is also showing antitumor activity. Other natural products, including those from plants (betulinic acid and shikonin), animals (bryostatins) and microbes (squalestatin and sophorolipids) have a multiplicity of potentially useful actions. Unexpected functions of known secondary metabolites are continuously being unraveled, and are fulfilling some of the needs of present day medicine and show great promise for the future.     

Bioactive compounds from marine actinomycetes

Actinomycetes are one of the most efficient groups of secondary metabolite producers and are very important from an industrial point of view. Among its various genera, Streptomyces, Saccharopolyspora, Amycolatopsis, Micromonospora and Actinoplanes are the major producers of commercially important biomolecules. Several species have been isolated and screened from the soil in the past decades. Consequently the chance of isolating a novel actinomycete strain from a terrestrial habitat, which would produce new biologically active metabolites, has reduced. The most relevant reason for discovering novel secondary metabolites is to circumvent the problem of resistant pathogens, which are no longer susceptible to the currently used drugs. Existence of actinomycetes has been reported in the hitherto untapped marine ecosystem. Marine actinomycetes are efficient producers of new secondary metabolites that show a range of biological activities including antibacterial, antifungal, anticancer, insecticidal and enzyme inhibition. Bioactive compounds from marine actinomycetes possess distinct chemical structures that may form the basis for synthesis of new drugs that could be used to combat resistant pathogens.     

Biologically active metabolites of the marine actinobacteria

This review systematically data on the chemical structure and biological activity of metabolites of obligate and facultative marine actinobacteria, published from 2000 to 2007. We discuss some structural features of the five groups of metabolites related to macrolides and compounds containing lactone, quinone and diketopiperazine residues, cyclic peptides, alkaloids, and compounds of mixed biosynthesis. Survey shows a large chemical diversity of metabolites actinobacteria isolated from marine environment. It is shown that, along with metabolites, identical to previously isolated from terrestrial actinobacteria, marine actinobacteria synthesize unknown compounds not found in other natural sources, including micro organisms. Perhaps the biosynthesis of new chemotypes bioactive compounds in marine actinobacteria is one manifestation of chemical adaptation of microorganisms to environmental conditions at sea. Review stresses the importance of the chemical study of metabolites of marine actinobacteria. These studies are aimed at obtaining new data on marine microorganisms producers of biologically active compounds and chemical structure and biological activity of new low-molecular bioregulators of natural origin.     

海洋放线菌盐孢菌属研究进展

1991年,Jensen等从热带及亚热带海洋样品中分离获得了放线菌目专性海洋放线菌类群MAR1。根据形态学特征、生理生化特征及16S rRNA基因分析,提议该类群为新属——盐孢菌属(Salinospora)。2005年,盐孢菌属被正式报道,并将Salinospora更正为Salinispora。盐孢菌属是放线菌目第一个被报道的专性海洋微生物属,可以产生丰富的活性次级代谢产物,使盐孢菌属成为海洋微生物研究的热点。短短几年内,相继报道了许多研究成果。本文从盐孢菌属的建立过程、属及所含种的分类特征、生理生态学研究、次级代谢产物和分子生物学研究等方面对盐孢菌属的研究进展进行综述。     

海洋真菌生物活性物质研究之管见

海洋真菌是活性海洋天然产物的重要来源,到目前为止,已从海洋真菌的发酵产物中分离鉴定了1,117个新化合物。介绍了海洋真菌次生代谢产物的研究历史、现状、特点、研究方法、存在问题及其在新药研究中的应用前景。     

Screening and identification of actinobacteria from marine sediments: Investigation of potential producers for antimicrobial agents and type I polyketides

Marine actinobacteria were isolated from the sediment samples collected in Xinghai Bay, Xiaoping Island and Changhai in Dalian, China. Fifteen selective media were employed, of which Humic acid-Vitamin medium recovered the highest number of isolates. Eleven of the 239 isolates obtained from the selective media were selected for further investigations based on colony morphology and pigment formation. Phylogenetic analysis of their 16S rRNA sequences showed that these strains belong to the genera of Streptomyces and Micromonospora. One of these strains identified is a new species of Streptomyces. Type I polyketide synthase (PKSI) gene fragments were amplified from three strains. The PKSI sequence of one of these strains (S187) showed high homology to the KS gene involved in meridamycin biosynthesis. Based on this result, the neurotrophic activity of S187 was further investigated. Culture broth of S187 was applied to rat pheochromocytoma (PC12) cells, and a 2.3-fold increase in growth over control cells was observed by the 3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide assay. These results indicated the importance of further exploration of the marine actinobacteria in Dalian sea area for antimicrobial agents and type I polyketides.     

基因组挖掘技术在海洋放线菌天然产物研究开发中的应用及展望

利用微生物的基因组信息预测其合成特定天然产物的潜能, 进而进行新化合物分离纯化和结构鉴定的基因组挖掘技术, 已经成为国内外研究的热点, 并在多种细菌和真菌的天然产物发现中得到成功应用。本文综述了基因组挖掘技术的最新进展, 包括生物信息分析和结构预测、基因组指导的天然产物的发现、沉默基因的激活和异源表达技术等, 以及我国学者开发的转录组挖掘技术, 并重点综述了影像质谱技术在基因组挖掘中的应用。目前对海洋放线菌进行基因组挖掘的研究还比较少, 而基因组挖掘技术的发展, 将极大地促进对海洋放线菌天然产物的发现和鉴定。未来除了充分挖掘可培养微生物的基因组, 对未培养微生物宏基因组的挖掘将进一步深入。此外, 除了开发利用基因组中合成天然产物的结构基因和调节基因, 还应该充分开发利用其他不同的遗传元件, 包括不同转录活性和响应不同环境条件和信号的启动子, 以及具有调节作用的RNA等。     

Isolation and characterization of tyrosinase produced by marine actinobacteria and its application in the removal of phenol from aqueous environment

The present study was focused on screening and characterization of tyrosinase enzyme produced by marine actinobacteria and its application in phenolic compounds removal from aqueous solution. A total of 20 strains were isolated from marine sediment sample and screened for tyrosinase production by using skimmed milk agar medium. Among 20 isolates, two isolates LK-4 and LK-20 showed zone of hydrolysis and these were taken for secondary screening by using tyrosiue agar medium. Based on the result of secondary screening LK-4 was selected for further analysis, such as tyrosinase assay, protein content and specific activity of the enzyme. The tyrosinase enzyme was produced in a SS medium and was partially purified by ammonium sulfate precipitation, dialysis and SDS PAGE. The isolate （LK-4） was identified as Streptomyces espinosus using 16S rRNA gene sequencing and named as ＂Streptomyces espinosus strain LK4 （KF806735）＂. The tyrosinase enzyme was immobilized in sodium alginate which was applied to remove phenolic compounds from water. The enzyme efficiently removed the phenolic compounds from aqueous solution within few hours which indicated that tyrosinasc enzyme produced by Streptomyces espinosus strain LK-4 can be potently used for the removal of phenol and phenolic compounds from wastewater in industries.     

海洋放线菌研究进展

海洋放线菌因其产生独特的次生代谢产物而备受世界的关注。本文以海洋放线菌的研究历史为主线,综述了海洋放线菌研究的发展历程,海洋放线菌的概念、生物资源、多样性及其分布状况、次生代谢产物以及基因组研究等方面,探讨了其生态功能,最后展望了我国海洋放线菌研究存在的问题及未来发展的前景。     

Two new secondary metabolites,saccharochlorines A and B,from a marine bacterium Saccharomonospora sp. KCTC-19160

Two new chlorinated secondary metabolites, saccharochlorines A and B (1 and 2), were isolated from the saline cultivation of a marine-derived bacterium Saccharomonospora sp. (KCTC-19160). The chemical structures of the saccharochlorines were elucidated by 2D NMR and MS spectroscopic data. Saccharochlorines A and B (1 and 2) exhibit weak inhibition of β-secretase (BACE1) in biochemical inhibitory assay, but they induced the release of Aβ (1–40) and Aβ (1–42) in H4-APP neuroglial cells. This discrepancy might be derived from the differences between the cellular and sub-cellular environments or the epigenetic stimulation of BACE1 expression.     

Marine actinomycetes as a source of novel secondary metabolites

A set of 600 actinomycetes strains which were isolated from marine sediments from various sites in the Pacific and Atlantic Oceans were screened for the production of bioactive secondary metabolites. Marine streptomycete strains were found to be producers of well known chemically diverse antibiotics isolated from terrestrial streptomycetes, as in the case of marine Micromonospora strains. New marine members of the rare genus Verrucosispora seem to be a promising source for novel bioactive secondary metabolites as shown in the case of the abyssomicin producing strain AB-18-032.     

In-silico study of seaweed secondary metabolites as AXL kinase inhibitors

AXL kinase is an attractive cancer target for drug design and it is involved in different cancers. A set of molecule databases with 1072 secondary metabolites from seaweeds were screened against the AXL kinase active site and eight molecules were shortlisted for further studies. From the docking analysis of the complexes, four molecules GA011, BE005, BC010, and BC005 are showing prominent binging. From the 100 ns of molecular dynamics simulations and ligand-bound complex MM-PBSA free energy analysis, two molecules BC010 (ΔG = −135.38 kJ/mol) and BE005 (ΔG = −141.72 kJ/mol) are showing molecule stability in the active site also showing very strong binding free energies. It suggests these molecules could be the potent molecules for AXL kinase.