Rhodococci are renowned for their great metabolic repertoire partly because of their numerous putative pathways for large number of specialized metabolites such as biosurfactant. Screening and genome-based assessment for the capacity to produce surface-active molecules was conducted on Rhodococcus sp. ADL36, a diesel-degrading Antarctic bacterium. The strain showed a positive bacterial adhesion to hydrocarbon (BATH) assay, drop collapse test, oil displacement activity, microplate assay, maximal emulsification index at 45% and ability to reduce water surface tension to < 30 mN/m. The evaluation of the cell-free supernatant demonstrated its high stability across the temperature, pH and salinity gradient although no correlation was found between the surface and emulsification activity. Based on the positive relationship between the assessment of macromolecules content and infrared analysis, the extracted biosurfactant synthesized was classified as a lipopeptide. Prediction of the secondary metabolites in the non-ribosomal peptide synthetase (NRPS) clusters suggested the likelihood of the surface-active lipopeptide production in the strain’s genomic data. This is the third report of surface-active lipopeptide producers from this phylotype and the first from the polar region. The lipopeptide synthesized by ADL36 has the prospect to be an Antarctic remediation tool while furnishing a distinctive natural product for biotechnological application and research.

Four preliminary screening methods for biosurfactant synthesis - drop collapse assay, oil displacement activity, microplate assay and emulsification index (E24) were compared and evaluated for their reliability and ease of use. All screening methods showed positive indications for the synthesis of biological surface-active agents. Nevertheless, partial collapse of the supernatant and low emulsification index (E24) of Pseudomonas sp. might signify a low production of biosurfactants. Based on our observation, both drop collapse and oil displacement assay is the fastest, easiest and most reliable analytical routine to be suggested to screen for biosurfactant-producing strains. In the extent for a high throughput screening (HTS), drop collapse assay is the best method for an accurate screening of biosurfactant producers.