A simple method for rapid screening of biosurfactant-producing strains using bromothymol blue alone

Abstract

Abstract Biosurfactants are deemed as green replacements of synthetic surfactants. Lipopeptides, a class of biosurfactants, have excellent surface active properties along with anti-microbial and anti-tumor activities. Identifying microorganisms producing high titre of lipopeptide is of great importance in reducing production cost as currently lipopeptide production is not commercially competitive. A quantitative colorimetric assay method was developed for detecting lipopeptides and high-throughput screening of lipopeptide-producing strains by mixing bromothymol blue solution (pH 7.2) with lipopeptide-containing samples resulting in an instantaneous and stable color change. This color change is quantified spectrophotometrically at 410 nm and 616 nm showing linearly quantitative response to increased concentrations of 3 major lipopeptides (surfactin, iturin and fengycin) at 0–1 g/l. The assay was used on both cell-free broth and crude extracts of lipopeptide-producing strains and the titre obtained from the assay was supported by HPLC data. This assay can be used for screening lipopeptide-producing strains and quantitatively detecting lipopeptides either in purified form or in cell-free broth.