Novel application of Nerium leaf and Image J software in drop collapse assay for rapid screening of biosurfactant producing microorganisms

Abstract

Biosurfactants are attractive molecules with varied applicationsmainly oil degradation, emulsification, bioremediation, therapeutics and conjugation of nanoparticles. The existing screening methods for biosurfactants are inappropriate and too tedious. Here, we have explored a novel approach with drop collapse assay wherein we replaced the microtiter well plate with the naturally hydrophobic Nerium (Nerium oleander L.) leaf. The stability of beaded drops on the leaf indicates negative phenomenon, and spreading of drop indicates positive phenomenon for surfactant property, as confirmed by the measuring drop diameter using Image J software. Fifty five bacterial cultures isolated from oil contaminated site were screened through this novel approach which revealed that the isolates DNM49 (6.75±0.29 mm), DNM50 (7.45±0.19 mm) and DNM51 (6.14±0.82 mm) were the best in terms of surface tension reduction, although thirty other isolates were also found to be positive. A gradation of activity in terms of surface tension reduction was also established based on drop diameter. The results demonstrated promising application of Nerium leaf with Image J software in drop collapse assay as an eco-friendly and cost-effective and technically authenticated alternative to the existing assays.