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Summary

Methyloversatilis universalis FAM5 is a facultative methylotrophic bacterium that has been found in a variety of natural and engineered ecosystems. The goal of this study was to investigate M. universalis FAM5 responses to different electron/carbon donors, e.g. methanol or ethanol, during anoxic growth in chemostats with nitrate as the electron acceptor. During steady-state anoxic growth on either methanol or ethanol, over 90% of the influent nitrate was reduced primarily to nitrite. The cell yield on methanol was lower, possibly due to high energy requirements for C1 assimilation. Label-free proteomics further revealed that methanol-grown cells displayed elevated concentrations of the enzymes involved in C1 metabolism (H4MPT/H4F pathways, formate oxidation and serine cycle). In contrast, C2 metabolism (glyoxylate shunt and tri-carboxylic acid cycle) and polyhydroxy-β-butyrate (PHB) synthesis related proteins were overrepresented during subsequent growth on ethanol. Notably, the expression of respiratory nitrate reductase was not affected by the carbon sources applied. Furthermore, the changes in the proteome upon switching back to methanol were mostly reversible. Therefore, M. universalis displays wide-ranging responses to adapt between growth on methanol and ethanol. Such metabolic versatility could be particularly useful in wastewater treatment systems, which need to switch between different electron donors, while still reliably meeting effluent nitrogen discharge goals.