Research on marine actinobacteria from A & N Islands is very scanty and till date these Island resources have not been properly explored to identify novel microorganisms with potential biological properties. With this outlook, the present research has been initiated to identify novel actinobacterial isolates from marine sediments of Minnie Bay, South Andaman Island. In this study, actinobacterial strains were isolated using modified growth medium. It has already been reported the usage of aged seawater enriched modified media for the isolation of marine actinobacteria . Various selective media were used for isolation and enumeration of actionobacteria [16, 37].
Streptomyces and Saccharopolyspora were found to be the dominant genera and their occurrence in Bay of Bengal was already reported . Frequency and dominance of Streptomyces in various sources have also been reported [11, 38, 39]. Majority of the isolates in this study possessed coiled mycelia and the same morphology has been reported by Roes and Meyer . Spore morphology is considered as one of the important characteristic features in actinobacterial identification and it varies among the genus and species [13, 41]. Moreover, the results acquired in this study have been outlined in Bergey’s Manual of Systematic Bacteriology  and Laboratory manual for identification of actinomycetes . Diversity of actinobacteria in Chesapeake Bay was also reported similar to our mode of observations . Based on growth studies, it was made known that majority of the isolates grew well in modified SCA medium. This has been already reported in actinobacterial community isolated from Bay of Bengal . Varied pigment production pattern was also observed among our isolates. Shirling and Gottileb  reported that the pigmentation prototype can be used as markers for identification. Moreover, cultural characteristics and utilization of carbon by the isolates in different media (ISP-2 to ISP-7) also play a major role in identification of actinobacteria to generic level. It is also proved that different physiological characteristics will certainly influence the growth rate of actinobacteria [44, 45].
Actinobacteria are the main basis of clinically significant antibiotics . Recent reports revealed that about 4,607 patents have been issued on actinobacteria related product and process. The genus Saccharopolyspora of Pseudonocardiaceae family is recognized for producing various antibiotics like vancomycin, erythromycin and rifamycins . Majority of our isolates exhibited appreciable antibacterial activity against tested clinical pathogens. Of three solvents used, ethyl acetate extract of Streptomyces sp. NIOT-VKKMA02 determined better inhibitory activity. Earlier report  also revealed the effectiveness of ethyl acetate extracts from actinobacteria for antibacterial studies with that of other solvents. For the first of its kind, Grein and Meyers  have reported on antagonistic marine actinobacteria. Of their 66 isolates from marine sediments of New Jersey and Florida, 50% demonstrated antibiotic activity against Gram positive and Gram negative bacteria. Modest information on antimicrobial potential of marine actinobacteria from A & N Islands was previously reported. Of 88 marine actinobacterial isolates, only three isolates revealed noticeable antibacterial activity among test pathogens . However, another report  disclosed that, of 42 isolates, only limited bioactivity (58.4%) was observed among test pathogens studied. As on date, our report will be the first to reveal a detailed study on antagonistic activity of marine actinobacteria from A & N Islands against both Gram positive and Gram negative eubacteria. In this study, majority of the isolates dominated in antibacterial potential against test pathogens. The reason may be the complex biochemical pathways adopted by our isolates due to the available nutrients and osmotic flux in sampling site.
Surfactants are amphiphilic compounds, produced by microorganisms of various classes including glycolipids, lipopeptides, fatty acids, phospholipids, neutral lipids and lipopolysaccharides . Applications of surfactants includes excellent detergency, emulsification, foaming, wetting, penetrating, thickening, microbial growth enhancements, metal sequestering and oil recovering. Surfactants are promising compounds and offer several advantages over chemically synthesized surfactants due to its lower toxicity, biodegradability and ecological acceptability . To our credit, Streptomyces sp. NIOT-VKKMA02 was found to have excellent emulsification property. Marine actinobacteria are good candidates for surfactant production, bioremediation and biodegradation . Halotolerant Streptomyces was reported to be a good surfactant producer . Based on literature survey, our study stands first in reporting surfactant production from marine actinobacteria of A & N Islands.
Growth survival studies of our isolates also accomplished to withstand in varied NaCl and pH levels. Based on previous reports, majority of the actinobacterial species isolated from marine sediments were moderate alkaliphilic and moderate halophilic in nature [6, 10, 11]. To cope with the external stress, these organisms have developed adaptive metabolic features to survive under extreme conditions . Nesterenkonia alba sp. nov., an alkaliphilic actinobacterium was reported to grow optimally at pH 9–10 . Chen et al.  also reported a halophilic marine actinomycete, Nocardiopsis litoralis sp. nov., isolated from a sea anemone.
Actinobacteria are physiologically diverse group in synthesizing various enzymes and metabolic products of industrial interest and are well recognized to produce most valuable pharmaceuticals and agrochemicals . Marine actinobacteria isolated from East and West coast of India were reported in the production of various industrial enzymes . Upon characterization for industrially potential enzymes, results from the potential isolates of our study revealed highly competent enzyme activity with that of previous reports. Bernfield  isolated several actinobacteria from marine sediments of the Central and West coast of Peru with multienzyme activity. Selvam et al.  reported 6.48 U/ml of amylase production from actinomycetes isolated from South Indian coastal region. While comparing with this result, Streptomyces sp. NIOT-VKKMA02 synthesized 13.27 U/ml of protease enzyme, which is two fold increases to that of previous report and the same augment was also recorded in cellulase production by the same strain. Hung-Der and Kuo-Shu  reported that the actinomycete, Streptomyces transformant T3-1 produced 2.6 U/ml of thermostable cellulase. Estimation of protease enzyme production also determined higher production level with the potential isolate. Ramesh et al.  2009 reported that, Streptomyces fungicidicus MML1614 isolated from Bay of Bengal produced 7.5 U/ml of thermostable alkaline protease. These results on enzymatic production authenticated the capability of our isolate to over synthesize the valuable enzymes of industrial importance. Phylogenetic analyses also make known that Streptomyces sp. NIOT-VKKMA02, Streptomyces sp. NIOT-VKKMA26 and Saccharopolyspora sp. NIOT-VKKMA22 form a separate cluster with Streptomyces griseus, Streptomyces venezuelae and Saccharopolyspora salina, respectively. To the best of our knowledge, this is the first report on detailed characterization on enzymes with industrial and pharmaceutical importance from three novel marine actinobacteria of A & N Islands.