Metabolomic imaging of a quaternary ammonium salt within a marine bacterial biofilm on carbon steel

•LASCA MSI technique allowed evaluation of quat biocide within a biofilm on steel.•Quat penetrated biofilm to 100 μm within 20 mins.•Entry of biocide at base of biofilm also detected.•Biocide and metabolites distributed heterogeneously both laterally and vertically.

A novel method to investigate penetration, distribution and metabolic effects of biocides in microbial biofilms is described. LASCA (laser ablation solvent capture by air flow) mass spectrometry imaging (MSI) allowed for the visualization of distributions of specific ion masses, including the signature of a quaternary ammonium salt biocide, benzyl dimethyl dodecyl ammonium chloride (BDDAC), throughout the biofilm. The biocide penetrated the upper layers of a Marinobacter sp. biofilm on a carbon steel coupon in seawater after 30 min. The concentration initially decreased with depth; however, it again increased close to the metal surface. Penetration of the biocide primarily occurred close to the center of the circular coupon, where ions with negative mass defects were preferentially detected, indicating that this is the anodic region of the corroding coupon. Future work using high performance liquid chromatography/mass spectrometry (HPLC/MS) will allow the identification within the biofilm of bacterial metabolites directly affected by biocide action.