Rhamnolipids Induced by Glycerol Enhance Dibenzothiophene Biodegradation in Burkholderia sp. C3

Abstract

Abstract In highly urbanized areas, pollution from anthropogenic activities has compromised the integrity of the land, decreasing soil availability for agricultural practices. Dibenzothiophene (DBT) is a heterocyclic aromatic hydrocarbon frequently found in urbanized areas, and is often used as a model chemical to study the microbial transformation of pollutants. The potential for human exposure and its health risk makes DBT a chemical of concern; thus, it needs to be environmentally managed. We utilized glycerol to stimulate Burkholderia sp. C3 in order to degrade DBT in respect to ① DBT biodegradation kinetics, ② bacterial growth, ③ rhamnolipid (RL) biosynthesis, and ④ RL secretion. Under an optimum glycerol-to-DBT molar ratio, the DBT biodegradation rate constants increased up to 18-fold and enhanced DBT biodegradation by 25%–30% at day 1 relative to cultivation with DBT alone. This enhancement was correlated with an increase in bacterial growth and RL biosynthesis. Proteomics studies revealed the enzymes involved in the upper and main steps of RL biosynthesis. The RL congeners Rha-C10-C10, Rha-Rha-C10-C10, Rha-Rha-C10-C12, and Rha-Rha-C12-C12 were identified in the medium supplemented with glycerol and DBT, whereas only Rha-C12-C12 was identified in cultures without glycerol or with RL inhibitors. The studies indicated that glycerol enhances DBT biodegradation via increased RL synthesis and bacterial growth. The results warrant further studies of environmental biostimulation with glycerol to advance bioremediation technologies and increase soil availability for agricultural purposes.