Abstract
The development of novel antibiotics with desirable properties from naturally available organisms is an on-going process in the field of microbial biotechnology. Mangroves are not extensively exploited for the isolation and screening of antimicrobial agents of the genus Streptomyces. The emergence of multidrug-resistant pathogens necessitates continuous search for novel antimicrobial agents. Also, searching of novel strains from pristine environments is an important approach for obtaining novel bioactive molecules. Streptomyces sp. AS4 was isolated from the mangroves. Antibiotic production was performed using substrates such as, apple pomace, pine apple peel, orange peel, rice bran, wheat bran, green gram husk, banana peel, pomegranate peel and black gram husk in solid state fermentation. Antibacterial activity was performed using Gram positive bacterial pathogen. The nutrient sources (carbon, nitrogen and ion) were optimized initially by one-variable-at-a-time approach and two level full factorial designs. In this study 129 actinomycetes were isolated from the mangroves. The isolates were assessed for their antibacterial activity. Among these isolates, Streptomyces sp. AS4 showed very strong antibacterial activity. Among these substrates, wheat bran showed enhanced production of antibiotics (209 U/g), whereas pomegranate peel supported very less quantity of antibiotics production (43 U/g) in a two level full factorial design. The process parameters were screened using traditional methods and statistical approach. Among the tested factors, moisture, yeast extract and CaCl2 significantly influenced the antibiotics production. Central composite design and response surface methodology enhanced antibiotics production by Streptomyces sp. AS4 by 10 fold than non-optimized medium. Streptomyces sp. AS4, a mangrove isolate showed hyper production of antibiotics. The strain AS4 utilized various agro-wastes including wheat bran for antibiotics production. Wheat bran proved to be a potent solid substrate for the production of antibiotics in an industrial scale. The actinomycetes strain, Streptomyces sp. AS4 and its antibiotics may have great application against various drug resistant organisms. (C) 2019 The Authors. Published by Elsevier B.V. on behalf of King Saud University.