BackgroundNew broad spectrum antimicrobial agents are urgently needed to combat frequently emerging multi drug resistant pathogens. Actinomycetes, the most talented group of microorganisms isolated from unexplored regions of the world may be the ultimate solution to this problem. Thus the aim of this study was to isolate several bioactive actinomycetes strains capable of producing antimicrobial secondary metabolite from Sundarbans, the only mangrove tiger land of the world.ResultsFifty four actinomycetes were isolated and analyzed for antimicrobial activity against fifteen test organisms including three phytopathogens. Nine morphologically distinct and biologically active isolates were subjected to polyphasic identification study.16 s rDNA sequencing indicated eight isolates to reveal maximum similarity to the genus streptomyces, whereas one isolate presented only 93.57 % similarity with Streptomyces albogriseolus NRRL B-1305T. Seventy-one carbon sources and twenty-three chemical sources utilization assay revealed their metabolic relatedness. Among these nine isolates three specific strains were found to have notably higher degree of antimicrobial potential effective in a broader range including phyto-pathogenic fungus. Finally the strain SMS_SU21, which showed antimicrobial activity with MIC value of 0.05 mg ml−1 and antioxidant activity with IC50 value of 0.242 ± 0.33 mg ml−1 was detected to be the most potential one. True prospective of this strain was evaluated utilizing GC-MS and the bioactive compound responsible for antimicrobial activity was purified.ConclusionRare bioactive actinomycetes were isolated from unexplored heritage site. Antimicrobial compound has also been identified and purified which is active against a broad range of pathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0495-4) contains supplementary material, which is available to authorized users.

The influence of temporal and spatial variations on the microbial community composition was assessed in the unique coastal mangrove of Sundarbans using parallel 16S rRNA gene pyrosequencing. The total sediment DNA was extracted and subjected to the 16S rRNA gene pyrosequencing, which resulted in 117 Mbp of data from three experimental stations. The taxonomic analysis of the pyrosequencing data was grouped into 24 different phyla. In general, Proteobacteria were the most dominant phyla with predominance of Deltaproteobacteria, Alphaproteobacteria, and Gammaproteobacteria within the sediments. Besides Proteobacteria, there are a number of sequences affiliated to the following major phyla detected in all three stations in both the sampling seasons: Actinobacteria, Bacteroidetes, Planctomycetes, Acidobacteria, Chloroflexi, Cyanobacteria, Nitrospira, and Firmicutes. Further taxonomic analysis revealed abundance of micro-aerophilic and anaerobic microbial population in the surface layers, suggesting anaerobic nature of the sediments in Sundarbans. The results of this study add valuable information about the composition of microbial communities in Sundarbans mangrove and shed light on possible transformations promoted by bacterial communities in the sediments.

The global knowledge of microbial diversity and function in Sundarbans ecosystem is still scarce, despite global advancement in understanding the microbial diversity. In the present study, we have analyzed the diversity and distribution of bacteria in the tropical mangrove sediments of Sundarbans using 16S rRNA gene amplicon sequencing. Metagenome is comprised of 1,53,926 sequences with 108.8 Mbp data and with 55 ± 2% G + C content. Metagenome sequence data are available at NCBI under the Bioproject database with accession no. PRJNA245459. Bacterial community metagenome sequences were analyzed by MG-RAST software representing the presence of 56,547 species belonging to 44 different phyla. The taxonomic analysis revealed the dominance of phyla Proteobacteria within our dataset. Further taxonomic analysis revealed abundance of Bacteroidetes, Acidobactreia, Firmicutes, Actinobacteria, Nitrospirae, Cyanobacteria, Planctomycetes and Fusobacteria group as the predominant bacterial assemblages in this largely pristine mangrove habitat. The distribution of different community datasets obtained from four sediment samples originated from one sampling station at two different depths providing better understanding of the sediment bacterial diversity and its relationship to the ecosystem dynamics of this pristine mangrove sediment of Dhulibhashani in, Sundarbans.

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Mangrove microbial communities and their associated activities have profound impact on biogeochemical cycles. Although microbial composition and structure are known to be influenced by biotic and abiotic factors in the mangrove sediments, finding direct correlations between them remains a challenge. In this study we have explored sediment bacterial diversity of the Sundarbans, a world heritage site using a culture-independent molecular approach. Bacterial diversity was analyzed from three different locations with a history of exposure to differential anthropogenic activities. 16S rRNA gene libraries were constructed and partial sequencing of the clones was performed to identify the microbial strains. We identified bacterial strains known to be involved in a variety of biodegradation/biotransformation processes including hydrocarbon degradation, and heavy metal resistance. Canonical Correspondence Analysis of the environmental and exploratory datasets revealed correlations between the ecological indices associated with pollutant levels and bacterial diversity across the sites. Our results indicate that sites with similar exposure of anthropogenic intervention reflect similar patterns of microbial diversity besides spatial commonalities.

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Microorganisms play a self-protective role by evolving their genetic and metabolic machinery to thrive in extreme environmental habitats. Halophiles are such salt-loving extremophilic microorganisms able to adapt, survive, and tend to grow at high salt concentrations. In this study, we have isolated Halobacillus sp. GSS1 from Sundarbans mangrove, India having a strong salt-tolerant ability (up to 4M) in Zobell Marine 2216 medium. The salt adaptation mechanism of Halobacillus sp. was investigated by Confocal microscopy using [Na+] specific dye, Sodium Green indicating the salt-in strategy for their osmoadaptation. Electron microscopic studies revealed that a contact-dependent cell-to-cell communication was profound among the Halobacillus sp. under nutrient limiting condition. This communication is mediated by nanotube, which is highly recommended for the exchange of molecular information between the two individual bacteria. The existence of the ymdB gene strongly supports our claim for nanotube formation by Halobacillus sp. GSS1. Surprisingly, Halobacillus sp. not only utilizing the nanotubes for communication, rather they desperately use nanotubes as a survival weapon under nutrient limiting conditions by triggering cannibalism. This is the first-ever report on the existence of nanotube mediated cell-to-cell communication and cannibalism in any halophilic bacteria, isolated from Sundarbans mangrove forest, India.

The rare, fastest-germinating, frequently invasive mucorale, Cunninghamella bertholletiae is intractable due to imprecise etiology. C. bertholletiae spores can infect both immunocompromised and immunocompetent individuals, to cause mucormycosis. Sub-optimal drug-susceptibility further limits its treatment options. The classical nasal drop, Anu Taila, is reported to be effective against the rather prevalent mucorale, Mucor spp., making its anti-mucormycotic effect against C. bertholletiae worth testing. The inhibitory effect of Anu Taila against C. bertholletiae was manifested as microstructural alterations of the spores and their delayed germination. Anu Taila reduced the germination-promoting reactive oxygen species (ROS) levels in both the pathogen, C. bertholletiae, and human host lung epithelial A549 cells. Expressions of structural (chitin synthase, trehalose synthase) and functional (cAMP-PKA) markers of spore germination were regulated by Anu Taila. cAMP-PKA expression and ROS generation are well-correlated, implicating the role of Anu Taila in delaying C. bertholletiae spore germination by targeting cAMP-PKA-mediated ROS generation. In conclusion, this study demonstrates that Anu Taila can create opportunity for host immune system to tackle the onset of C. bertholletiae infection by delaying its pathogenesis. This can be further leveraged to reinforce the host immune system through combinatorial treatment to prevent establishment of the Mucormycosis infection.