New Dimensions of Research on Actinomycetes: Quest for Next Generation Antibiotics

Starting with the discovery of streptomycin, the promise of natural products research on actinomycetes has been captivat¬ing researchers and offered an array of life-saving antibiotics. However, most of the actinomycetes have received a little attention of researchers beyond isolation and activity screening. Noticeable gaps in genomic information and associated biosynthetic potential of actinomycetes are mainly the reasons for this situation, which has led to a decline in the discovery rate of novel antibiotics. Recent insights gained from genome mining have revealed a massive existence of previously unrecognized biosynthetic potential in actinomycetes. Successive developments in next-generation sequencing, genome editing, analytical separation and high-resolution spectroscopic methods have reinvigorated interest on such actinomycetes and opened new avenues for the discovery of natural and natural-inspired antibiotics. This article describes the new dimensions that have driven the ongoing resurgence of research on actinomycetes with historical background since the commencement in 1940, for the attention of worldwide researchers. Coupled with increasing advancement in molecular and analytical tools and techniques, the discovery of next-generation antibiotics could be possible by revisiting the untapped potential of actinomycetes from different natural sources

Taxonomic and antimicrobial profiles of a rare actinomycete isolated from an inland solar saltern (India)

428-434<span style="font-size:9.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-bidi-font-family:="" "times="" roman";mso-ansi-language:en-gb;mso-fareast-language:en-us;="" mso-bidi-language:hi"="" lang="EN-GB">Rare actinomycetes from unexplored natural habitats nourish current natural compound screening programs. A rare actinomycete strain designated JAJ70; previously isolated from a hypersaline solar saltern was selected for its antimicrobial activities against bacteria and fungi. In the current study, the strain JAJ70 was studied at phenotypic and genotypic level for its proper assignment under rare genus Actinoalloteichus.  Comparison of the morphological and physiological characteristics of JAJ70 with those of already known species of Actinoalloteichus showed significant divergence. Analysis of the almost complete 16S rDNA sequence of strain JAJ70 showed a similarity level ranging between 97 and 99.6% within validly reported Actinoalloteichus species. Strain JAJ70 showed significant antimicrobial activity against a range of fungal strains and clinical pathogens including <span style="font-style:normal;mso-bidi-font-style: italic">Methicillin-resistant Staphylococcus aureus. In fact, the broad-spectrum activity exhibited by JAJ70 implies the need of further characterization of active antibiotic fraction from the crude extract and subsequent identification of responsible gene clusters to uncover its industrial and biotechnological significance. </span

Formulation and Statistical Optimization of Culture Medium for Improved Production of Antimicrobial Compound by Streptomyces sp. JAJ06

Streptomyces sp. JAJ06 is a seawater-dependent antibiotic producer, previously isolated and characterised from an Indian coastal solar saltern. This paper reports replacement of seawater with a defined salt formulation in production medium and subsequent statistical media optimization to ensure consistent as well as improved antibiotic production by Streptomyces sp. JAJ06. This strain was observed to be proficient to produce antibiotic compound with incorporation of chemically defined sodium-chloride-based salt formulation instead of seawater into the production medium. Plackett-Burman design experiment was applied, and three media constituents, starch, KBr, and CaCO3, were recognised to have significant effect on the antibiotic production of Streptomyces JAJ06 at their individual levels. Subsequently, Response surface methodology with Box-Behnken design was employed to optimize these influencing medium constituents for the improved antibiotic production of Streptomyces sp. JAJ06. A total of 17 experiments were conducted towards the construction of a quadratic model and a second-order polynomial equation. Optimum levels of medium constituents were obtained by analysis of the model and numerical optimization method. When the strain JAJ06 was cultivated in the optimized medium, the antibiotic activity was increased to 173.3 U/mL, 26.8% increase as compared to the original (136.7 U/mL). This study found a useful way to cultivate Streptomyces sp. JAJ06 for enhanced production of antibiotic compound

<span style="mso-bidi-font-weight:bold">Molecular phylogeny and plant growth promoting traits of endophytic bacteria isolated from roots of seagrass <i>Cymodocea serrulata</i> </span>

571-579In this study, phylogeny and growth promoting attributes of bacterial endophytes isolated from root tissue of seagrass were investigated. Sequence analysis of 16S rDNA among the isolates displayed the presence of bacterial members affiliated to six different genera: Vibrio, Photobacterium, Bacillus, Aerococcus, Saccharomonospora and Kocuria. Most of the isolates shared high level 16S rDNA sequence similarity with bacteria previously reported from marine water column, crustaceans, corals and terrestrial rhizosphere. Plant growth promoting (PGP) attributes including ability to fix nitrogen, solubilize phosphate and produce ammonia, acetoin and indolic compound were assessed in all the isolates. Genetically diverse, endophytic isolates with different PGP abilities showed close relatedness with bacterial inhabitants of marine ecosystem and likely to have ecological relevance. It implies the need of further studies to validate the relationship between the isolated endophytes and seagrass for sustenance of marine ecology

Characterization of Antibiotic Producing Rare Actinomycete Nonomuraea sp. JAJ18 Derived from an Indian Coastal Solar Saltern

Rare actinomycete genera are accepted as a promising source of novel metabolites having pharmaceutical importance. One such genus of rare actinomycete is Nonomuraea. The present study was aimed at characterizing the antibiotic producing Nonomuraea strain JAJ18 which was previously isolated from coastal solar saltern. Strain JAJ18 was recognized as a member of genus Nonomuraea based on its almost complete 16S rRNA gene sequence and phenotypic characteristics. The strain JAJ18 was found to be closely related to Nonomuraea maheshkhaliensis 16-5-14T (98.90%), Nonomuraea candida HMC10T (98.58%), and Nonomuraea jabiensis A4036T (98.43%). From cell-free culture broth of strain JAJ18, an antibiotic was extracted and purified by silica column chromatography. The obtained antibiotic was found to be active against a range of Gram-positive and Gram-negative bacteria including drug-resistant Staphylococcus, with minimal inhibitory concentration (MIC) ranging from 0.5 to 16.0 µg mL−1. The structural characteristics of antibiotic were determined by FTIR and NMR spectroscopy. The antibiotic was identified to be an aliphatic rich compound with significant dissimilarity to known antibiotics reported from members of the genus, Nonomuraea. As the trends to discover novel metabolites from Nonomuraea are vibrant, further studies are needed to understand the structural and biotechnological significance of antibiotic compound produced by Nonomuraea sp. JAJ18

Short-term in situ shading effectively mitigates linear progression of coral-killing sponge Terpios hoshinota.

The coral-killing sponge, Terpios hoshinota is a global invasive species that has conquered coral patches within a short span of time, which has led to a significant decline in living coral cover at various geographical locations. In this study, we surveyed the linear progression and impact of the Terpios invasion on live coral patches along Palk Bay, Indian Ocean, from August 2013 to August 2015. The field inventory revealed an extensive fatality rate of 76% as a result of Terpios outbreak. Experimental findings showed that symbiotic cyanobacteria act as a nutritional factory for the aggressive growth of Terpios. Shading hypothetically impairs the nutritional symbiont of the invasive species: the effect of sunlight on cyanobacterial biomass and its influence on Terpios progression over live coral patches was tested through in situ shading experiments. This study showed that artificial shading with cotton fabric could effectively mitigate sponge growth on live coral without affecting coral homeostasis

Correction: Short-term in situ shading effectively mitigates linear progression of coral-killing sponge Terpios hoshinota.

[This corrects the article DOI: 10.1371/journal.pone.0182365.]