Problem statement:The exhaustion of the usual terrestrial sources and the rise of resistant pathogens dictate the search for novel actinomycetes and new antibiotics. In this context, niche habitats such as caves, pristine forests, lakes, rivers, and other wetlands, high salt environments, marine ecosystems and endophytic niches are promising targets for survey of bioactive actinomycetes. Approach: Actinomycetes were isolated from several niche habitats in Manipur, India, on selective media such as SCNA and Chitin agar with or without antibiotics. Selected isolates were subjected to antimicrobial activity screening by Kirby-Bauer method. Results: 172 lake sediment (SCNA, LS1 series), 35 lake sediment (CA, LSCH series), 120 river (NRP, NRB and..series), 39 forest (AML series), 35 cave (KC1 series), 101 salt spring (NH, N3S and .. series), 46 Shirui jungle (SJ series) and 66 Shirui hill (SH series) actinomycetes isolates were obtained. Of 99 randomly selected isolates screened, 37 had antimicrobial activities against 1 or more indicator strains: 32 against Gram positive bacteria and 8 against Gram negative bacteria; 10 actinomycete strains were antimycotic and 3 had broad-spectrum antibiotic activities. About 18 potent antibacterial, 1 anti pseudomonas, 1 exclusively antifungal and 3 broad-spectrum antimicrobial actinomycetes were chosen for further studies. Conclusion: Niche habitats in Manipur especially wetlands show great promise for discovery of bioactive actinomycetes.

As part of our ongoing studies on actinomycete diversity in Manipur, an underexplored zone falling in the Indo-Burma biodiversity hotspot, this paper reports bioactivity screening and characterization of bioactive actinomycetes from Nambul River. Bioprospecting studies on actinobacteria have been largely focused on terrestrial and, more recently, on marine ecosystems but freshwater habitats have been largely neglected and studies on freshwater actinomycetes are very scanty in India. Hence we investigated the actinomycete diversity in one of the freshwater rivers of Manipur, Nambul River in Manipur, India. A total of 156 actinomycetes were isolated from three samples of Nambul River. Based on the results of primary screening, 23 isolates were selected for secondary screening. Nine strains showed significant antibacterial or broad spectrum antimicrobial (antibacterial and antifungal) activities in the secondary screening. Phylogenetic analyses indicated that a majority of them were Streptomyces species though some rare actinobacteria were also recovered. Seven strains were identified as Streptomyces spp. while one strain each was identified as Nocardia sp. and Micromonospora sp. Three strains showed promising antifungal activities against human and plant pathogens. This study highlights the potential for discovering bioactive actinomycetes in underexplored niche biotopes such as river sediments.

A novel actinobacterial strain, MBRL 353T, was isolated from a sample collected from a limestone quarry at Hundung, Manipur, India. Comparison of 16S rRNA gene sequences of strain MBRL 353T and other members of the genus Rhodococcus showed sequence similarities ranging from 95.5 to 98.2 %, with strain MBRL 353T showing closest sequence similarity to Rhodococcus triatomae IMMIB RIV-085T (98.2 %) and Rhodococcus equi DSM 20307T (97.2 %). DNA–DNA hybridization results, however, revealed that DNA–DNA relatedness values between strain MBRL 353T and R. triatomae DSM 44892T (43.4 %) and R. equi DSM 20307T (33.4 %) were well below the 70 % limit for species identification. Strain MBRL 353T contained meso-diaminopimelic acid as the diagnostic diamino acid and galactose and arabinose in the cell wall. Mycolic acids were present. The major fatty acids were C16 : 0 (45.7 %), C18 : 1ω9c (18.2 %) and 10-methyl C18 : 0 (11.3 %). The only menaquinone detected was MK-8(H2), while the major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside and one unknown phospholipid. The G+C content of the genomic DNA was 69.2 mol%. The phenotypic and genotypic data showed that strain MBRL 353T merits recognition as a representative of a novel species of the genus Rhodococcus for which the name Rhodococcus canchipurensis sp. nov. is proposed; the type strain is MBRL 353T ( = KCTC 19851T = JCM 17578T).

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