Use of SWATH mass spectrometry for quantitative proteomic investigation of Shewanella oneidensis MR-1 biofilms grown on graphite cloth electrodes.

Quantitative proteomics from low biomass, biofilm samples is not well documented. In this study we show successful use of SWATH-MS for quantitative proteomic analysis of a microbial electrochemically active biofilm. Shewanella oneidensis MR-1 was grown on carbon cloth electrodes under continuous anodic electrochemical polarizations in a bioelectrochemical system (BES). Using lactate as the electron donor, anodes serving as terminal microbial electron acceptors were operated at three different electrode potentials (+0.71 V, +0.21 V & -0.19 V vs. SHE) and the development of catalytic activity was monitored by measuring the current traces over time. Once maximum current was reached (usually within 21-29 h) the electrochemical systems were shut off and biofilm proteins were extracted from the electrodes for proteomic assessment. SWATH-MS analysis identified 704 proteins, and quantitative comparison was made of those associated with tricarboxcylic acid (TCA) cycle. Metabolic differences detected between the biofilms suggested a branching of the S. oneidensis TCA cycle when grown at the different electrode potentials. In addition, the higher abundance of enzymes involved in the TCA cycle at higher potential indicates an increase in metabolic activity, which is expected given the assumed higher energy gains. This study demonstrates high numbers of identifications on BES biofilm samples can be achieved in comparison to what is currently reported. This is most likely due to the minimal preparation steps required for SWATH-MS.
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