A Straightforward Assay for Screening and Quantification of Biosurfactants in Microbial Culture Supernatants.

Sonja Kubicki,Karl-Erich Jaeger,Till Tiso,Silke Jankowski,Stephan Thies,Kerstin Schipper,Michael Feldbrügge,Isabel Bator,Lars M Blank

doi:10.3389/fbioe.2020.00958

Abstract

A large variety of microorganisms produces biosurfactants with the potential for a number of diverse industrial applications. To identify suitable wild-type or engineered production strains, efficient screening methods are needed, allowing for rapid and reliable quantification of biosurfactants in multiple cultures, preferably at high throughput. To this end, we have established a novel and sensitive assay for the quantification of biosurfactants based on the dye Victoria Pure Blue BO (VPBO). The assay allows the colorimetric assessment of biosurfactants directly in culture supernatants and does not require extraction or concentration procedures. Working ranges were determined for precise quantification of different rhamnolipid biosurfactants; titers in culture supernatants of recombinant Pseudomonas putida KT2440 calculated by this assay were confirmed to be the same ranges detected by independent high-performance liquid chromatography (HPLC)-charged aerosol detector (CAD) analyses. The assay was successfully applied for detection of chemically different anionic or non-ionic biosurfactants including mono- and di-rhamnolipids (glycolipids), mannosylerythritol lipids (MELs, glycolipids), 3-(3-hydroxyalkanoyloxy) alkanoic acids (fatty acid conjugates), serrawettin W1 (lipopeptide), and N-acyltyrosine (lipoamino acid). In summary, the VPBO assay offers a broad range of applications including the comparative evaluation of different cultivation conditions and high-throughput screening of biosurfactant-producing microbial strains.

Highlights

Microbial biosurfactants are a structurally heterogeneous group of secondary metabolites
Surface active natural products are for instance glycolipids like rhamnolipids, trehalolipids, sophorolipids, and mannosylerythritol lipids (MELs) as well as lipopeptides surfactin, serrawettin W1, N-acylamino acids, or polymers like emulsan
We have demonstrated the suitability of the Victoria Pure Blue BO (VPBO) assay to detect chemically different biosurfactants in culture supernatants, namely, the non-ionic glycolipid MEL produced by Ustilago maydis MB215, the lipopeptide serrawettin W1 produced by recombinant P. putida KT2440, and N-acyltyrosines in culture supernatants from Escherichia coli DH10b

Summary

Introduction

Microbial biosurfactants are a structurally heterogeneous group of secondary metabolites. Surface active natural products are for instance glycolipids like rhamnolipids, trehalolipids, sophorolipids, and mannosylerythritol lipids (MELs) as well as lipopeptides (or lipoamino acids like) surfactin, serrawettin W1, N-acylamino acids, or polymers like emulsan The best-known producer of rhamnolipids is the bacterial pathogen Pseudomonas aeruginosa; sophorolipids and MELs are produced with high titers by different yeasts. These glycolipids are discussed for many applications, e.g., in cosmetics, household detergents, or environmental remediation (Khan et al, 2014). Many lipopeptides are well-known for their pronounced bioactivities; an example is serrawettin W1 which is naturally produced by the pathogenic bacterium Serratia marcescens DSM12481 (Gudiña et al, 2016; Hage-Hülsmann et al, 2018)

Methods

Results

Conclusion