Bioactive Metabolites from Streptomyces nanhaiensis VSM-1: Polyphasic Taxonomy, Optimization, and Evaluation of Antimicrobial Metabolites by GC-MS Analysis

Abstract

Actinomycetes strain VSM-1 isolated from the marine sediment samples of north coastal Bay of Bengal was identified as Streptomyces nanhaiensis by conventional and molecular approaches. S. nanhaiensis recorded significant broad-spectrum activity against all human and plant pathogenic microorganisms tested. An attempt has been made to evaluate the influence of medium components on the antimicrobial metabolite production of VSM-1 and to optimize an effective fermentation medium to enhance its bioactive metabolite yield. Bioactive metabolite production by VSM-1 was initially optimized using one-factor-at-a-time (OFAT) method where the yield of metabolites was recorded to generate inhibition zones of 30, 29, 28, 27, and 29 mm against test microorganisms, i.e., Shigella flexneri, Serratia marcescens, Proteus vulgaris, Pseudomonas aeruginosa, and medically important dermatophyte Candida albicans. The optimal values obtained from OFAT were selected, and the experimental model was designed using response surface methodology. Central composite design (CCD) was employed to study the influence of the variables on the production of bioactive metabolites by VSM-1 and their effect on the responses (test microorganisms). The statistical analysis showed that the variables which have a significant effect (P < 0.001) on the metabolite production at both the interactive and individual levels were measured in terms of antimicrobial activity. Maximum yield of metabolites was recorded to generate increased zones of inhibition, i.e., 34.2, 32, 31.6, 32.3, and 33.6 mm, against test microorganisms Shigella flexneri, Serratia marcescens, Proteus vulgaris, Pseudomonas aeruginosa, and Candida albicans, respectively. Unstructured kinetic models were used to fit the results obtained from experiments, and kinetic parameters were also estimated. Further, chemometric profile of the ethyl acetate extract of the strain was performed by gas chromatography and mass spectroscopy (GC-MS). Interpretation on mass spectrum of GC-MS was carried out using NIST Mass Spectral Data Base, with NIST MS search v.2.0. The results of the present study revealed the presence of various active principles with a diverse range of positive pharmacological actions, and hence this strain could be a possible source of novel bioactive compounds.