Research article from the ERA Chair and collaborators from The University of Queensland, Ehime University, Technical University of Munich, and LanzaTech published in mSystems reports for the first time absolute proteome quantification in a gas-fermenting acetogen. The authors employed a comprehensive state-of-the-art workflow to quantify intracellular concentrations for >1,000 proteins that revealed, for example, prioritisation of proteome resources, potentially relevant isoenzymes in vivo, and that flux adjustments in the model-acetogen Clostridium autoethanogenum are dominantly controlled at the post-translational level. This work advances both rational metabolic engineering of acetogen cell factories and accurate in silico reconstruction of their phenotypes.