Post-translational modifications, such as protein acetylation, are important for the regulation of protein function. Protein acetylation is widespread in Escherichia coli, but so far only one deacetylase, CobB, has been identified. To find new deacetylases, Tu, Guo and Chen et al. developed a 'clip-chip' assay, in which proteins with potential enzymatic activity are arrayed on a glass slide and clipped to a slide with substrate. The serine hydrolase YcgC mediated the loss of acetylation of several substrates, which were distinct from those substrates targeted by CobB. YcgC homologues have been found in other bacteria and a selection of these homologues were tested in vivo, confirming their deacetylase activity. Thus, YcgC and its homologues represent a new family of deacetylases in bacteria and a new type of deacetylase as none of the previously identified enzymes are serine hydrolases.