Cometabolic transformation of linear alkylbenzenesulphonates by methanotrophs

Cometabolic transformation of commercial linear alkylbenzenesulphonates (LAS) and pure congeners of 2-[4-(sulphophenyl)]nonan (2C9LAS) and 2-[4-(sulphophenyl)]decan (2C10LAS) was studied by using a mixed methanotrophic-heterotrophic culture MM1 and a pure culture of type II methanotroph (strain CSC1), isolated from culture MM1. Cultures were grown in shake flasks under conditions promoting expression of the soluble methane monooxygenase (sMMO). Both the mixed culture MM1 and the pure culture CSC1 were capable of transforming LAS with or without methane as the natural substrate. Experiments performed without methane (resting cells) showed faster cometabolic transformation of LAS congeners with longer alkyl side-chains. Both 2C9LAS and 2C10LAS congeners were transformed significantly faster at 30°C, although the optimum temperature for the growth of mixed culture MM1 was 20°C. Simultaneous methane oxidation and LAS transformation, and their mutual competitive inhibition, indicated the involvement of the MMO enzyme system and possible methanotrophic activity in the initiation of cometabolic LAS transformation. The capability of two heterotrophic species to transform sulphophenyldecanoic acid suggests possible heterotrophic activity in further LAS transformation (β-oxidation). Faster LAS transformation by mixed culture MM1 than by pure culture CSC1 suggested that methanotrophic-heterotrophic interactions are important for transformation of the complex LAS molecule.