Carbonyl reduction by YmfI in Bacillus subtilis prevents accumulation of an inhibitory EF-P modification state.

Translation elongation factor P (EF-P) in Bacillus subtilis is required for a form of surface migration called swarming motility. Furthermore, B. subtilis EF-P is post-translationally modified with a 5-aminopentanol group but the pathway necessary for the synthesis and ligation of the modification is unknown. Here we determine that the protein YmfI catalyzes the reduction of EF-P-5 aminopentanone to EF-P-5 aminopentanol. In the absence of YmfI, accumulation of 5-aminopentanonated EF-P is inhibitory to swarming motility. Suppressor mutations that enhanced swarming in the absence of YmfI were found at two positions on EF-P, including one that changed the conserved modification site (Lys 32) and abolished post-translational modification. Thus, while modification of EF-P is thought to be essential for EF-P activity, here we show that in some cases it can be dispensable. YmfI is the first protein identified in the pathway leading to EF-P modification in B. subtilis, and B. subtilis encodes the first EF-P ortholog that retains function in the absence of modification.