Background The NADH:ubiquinone oxidoreductase (Nuo) is an assembly of proteins also known as complex I. It is the entry point for highly energetic electrons in the classical aerobic respiration process as it couples the transfer of two electrons from NADH to ubiquinone with proton pumping resulting in the establishment of a proton mortice force. It was assumed that to fulfil its function, the complex must contain at least 14 subunits. Yet the presence of an 11-subunit version of complex I as detected in genomic and proteomic analyses of strict anaerobes such as sulfate-reducing bacteria (SRB) or organohalide-respiring bacteria (OHRB) raised for the latter the question of its potential implication in the still poorly understood respiratory processes. Moreover, the 11-subunits complex I lacks the NADH oxidizing module suggesting the use of an alternative electron donor. Methods The goal of this work is to elucidate the role of complex I in the specific context of OHRB with a focus on Firmicutes. During organohalide respiration (OHR), organohalide compounds serve as final electron acceptors in an energy-conserving process. The complete picture of the electron transfer chain remains elusive and a good understanding of the proteins involved in this metabolism is of great interest for bioremediation. The development of targeted quantitative proteomics will serve to compare the abundance of the complex in Desulfitobacterium hafniense strain DCB-2 when cultivated in different growth conditions. This facultative OHRB is capable of using different combinations of electron donors/acceptors and offers the possibility to evaluate the prevalence of the complex in one or the other growth condition, reflecting its importance. Results Progress in the method development and preliminary proteomic data will be discussed. Conclusion In parallel, the biochemical characterization of the complex in Dehalobacter restrictus is currently under investigation by Blue Native PAGE to define its protein composition and identify possible electron donor candidates