Diversity and plasticity of simultaneously expressing extracellular protease inhibitors from four marine Streptomyces spp. isolated from West coast of India

Streptomyces have long been studied for their defense metabolites and Protease Inhibitors (PIs) they secrete for mediating biotic interactions. Current study focuses on diversity of extracellular PIs obtained from four marine Streptomyces species isolated from intertidal regions of West Coast of India. Streptomyces PIs showed strong inhibition of subtilisin followed by trypsin and chymotrypsin. Using shotgun proteomics approach, we identified 15 Streptomyces PIs belonging to 4 PI families namely Streptomyces subtilisin inhibitor (SSI), Potato peptidase inhibitor, Ovomucoid and Serpin. This is a first report of identification of Ovomucoid and Potato peptidase inhibitor families from Streptomyces . Amongst the 15 PIs, 12 were SSIs with 20-75% sequence similarity and variations in the conserved 73 rd aa residue. Moreover, 10 SSI isoforms were co-expressed in a single species S. longispororuber. In-silico and in-vitro assays with proteases from microbial, bovine and insect sources suggested that the Streptomyces PIs had a broad-spectrum inhibitory activity. In co-culture of Streptomyces with other protease producing bacteria, cellular secretions differentially affected growth, sporulation and/or pigment production. Present study elucidates the diversity and plasticity of extracellular PIs from marine Streptomyces spp. Further, their role in chemical ecology of the bacterial communities as well as their potential applications in therapeutics are discussed.