Diversity of Biosurfactant-producing Streptomyces Isolates from Hydrocarbon-contaminated Soil

Actinomycetes are unsurpassed as producers of bioactive metabolites, primarily those with antimicrobial/anticancer properties; however, their capacity for producing other natural products such as biosurfactants, has been less explored. Biosurfactants are heterogeneous surface active compounds and can be potentially deployed for bioremediation of hydrocarbons and as emulsifying agents in agriculture, pharmaceutical and food industries. In this study, Streptomyces was selectively isolated and characterized from hydrocarbon-contaminated soil. The isolates were dereplicated based on morphology and antimicrobial properties and representative isolates screened for biosurfactant production using drop-collapse test, emulsification assay and bacterial adherence to hydrocarbons (BATH) test. Streptomyces sp. PN-18 exhibited high antimicrobial activity, significant cell-surface hydrophobicity (>95%) and emulsification activity (>70 EU mL). The best production medium was found to be tryptone soy broth in which emulsification activity increased to 110 EU mL with emulsification index (E24) of 65%. Nearly complete 16S rDNA sequence analysis (GenBank accession GQ856644) of PN-18 showed similarity to S. rochei (97.9%), though with significant differences in morphological and physiological characteristics. The study demonstrates Streptomyces diversity in hydrocarbon-impacted environments and the possibility of exploiting PN-18 for bioremediation.