Production of a broad spectrum streptothricin like antibiotic from halotolerant Streptomyces fimbriatus isolate G1 associated with marine sediments.

Streptomyces have been reported as a remarkable source for bioactive secondary metabolites with complex structural and functional diversity. In this study, 35 isolates of genus Streptomyces were purified from rhizospheric and marine soils collected from previously unexplored habitats and screened for antimicrobial activities. One of these isolates, G1, when tested in vitro, was found highly active against wide range of microbes including Gram-positive, Gram-negative bacteria, and different fungal pathogens. It was identified as mesophilic, alkaliphilic, and moderately halotolerant as it showed optimum growth at temperature 30 °C, pH 8.0 in casein-starch-peptone-yeast extract-malt extract medium supplemented with 5% NaCl. Sequence analysis of the 16S rRNA gene indicated 100% identity of this isolate to Streptomyces fimbriatus. Moreover, maximum antimicrobial activity was achieved in starch nitrate medium supplemented with 1% glycerol as carbon and 0.03% soy meal as nitrogen source. The antimicrobial compounds produced by this isolate were extracted in methanol. Bioassay-guided fractionation through thin layer chromatography of methanolic extract resulted in the separation of a most active fraction with an Rf value of 0.46. This active fraction was characterized by FTIR and LCMS analysis and found similar to streptothricin D like antibiotic with m/z 758.42.

Empirical evidence of cold stress induced cell mediated and humoral immune response in common myna (Sturnus tristis).

Common myna (Sturnus tristis) is a bird indigenous to the Indian subcontinent that has invaded many parts of the world. At the onset of our investigation, we hypothesized that the immunological profile of myna makes it resistant to harsh/new environmental conditions. In order to test this hypothesis, a number of 40 mynas were caught and divided into two groups, i.e., 7 and 25 °C for 14 days. To determine the effect of cold stress, cell mediated and humoral immune responses were assessed. The macrophage engulfment percentage was significantly (P < 0.05) higher at 25 °C rather than 7 °C either co-incubated with opsonized or unopsonized sheep red blood cells (SRBC). Macrophage engulfment/cell and nitric oxide production behaved in a similar manner. However, splenic cells plaque formation, heterophil to lymphocyte (H/L) ratio, and serum IgM or IgG production remained non-significant. There was a significant increase of IgG antibody production after a second immunization by SRBC. To the best of our knowledge, these findings have never been reported in the progression of this bird's invasion in frosty areas of the world. The results revealed a strengthened humoral immune response of myna and made this bird suitable for invasion in the areas of harsh conditions.