Lactic acid is a valuable organic acid that can be produced by fermentation of renewable sugar. Lactate productivity can be increased by retaining cells within the reactor, enabling continuous operation with higher cell concentrations. Biofilms are an inexpensive cell immobilization method. While much is known about the differences in physiology and metabolism of pathogenic biofilms, biofilms relevant to industrial processes are less characterized. The goal of this study was to identify metabolic features of biofilm metabolism of Lactobacillus delbrueckii ssp. lactis using quantitative proteomics. Compounds in biofilm samples negatively affected LC-MS/MS performance, indicating the importance of sample precipitation. Among other differences, proteins associated with metabolic processes such as fatty acid biosynthesis and metal oxidation were more abundant in biofilm cells, as were proteins associated with stress. This is the first proteomic study of a Lactobacillus species in biofilms with relevance to industrial biotechnology. (c) 2018 American Institute of Chemical Engineers