Procedure for Rhamnolipids Quantification Using Methylene-blue

Abstract

Rhamnolipids produced by Pseudomonas aeruginosa (P. aeruginosa) represent a group of biosurfactants with various applications (e.g., bioremediation of oil spills, cosmetics, detergents and cleaners). The commonly used colorimetric methods for rhamnolipid quantification, including anthrone, phenol−sulfuric acid and orcinol based quantification (Helbert and Brown, 1957; Chandrasekaran and BeMiller, 1980), are laborious and operationally hazardous because of the strong acid/chemical emanation which can cause deterioration of instruments measurements (e.g., spectrophotometer). Therefore, the methylene-blue-based analysis appears as a promising alternative to safely quantify whole rhamnolipid molecules based on chemical complexation reaction (Pinzon and Ju, 2009). Indeed, methylene blue and rhamnolipids form a complex in a water-chloroform phase system. The rhamnolipids-methylene blue complex is partitioned into the chloroform phase which will develop a blue color that can be quantified at 638 nm to deduce rhamnolipids concentration. Here, we describe a variant of methylene-blue-based rhamnolipids quantification procedure that allows spectrophotometric quantification on standard 96-well plastic microplate contrarily to original methylene blue procedure that requires specific and expensive microplate due to chloroform chemical properties.