Horizontal transfer of post-translational modifiers brings evolutionary opportunity and challenges to a conserved...

Horizontal gene transfer (HGT) is a major driver of microbial evolution, yet the influence of host cellular context on the integration and functionality of transferred genes remains underexplored. In this study, we investigate how host background impacts the horizontal acquisition of post-translational modification (PTM) machinery. Here, we use heterologous expression of the highly conserved and frequently horizontally transferred translational elongation factor P (EF-P) from diverse species in Escherichia coli as a model. EF-P has a heterogenous relationship with PTMs; three characterized variants each undergo distinct PTM pathways, while others function effectively without any modification.

We demonstrate that EF-P from Deinococcus radiodurans, Geoalkalibacter ferrihydriticus, and Nitrosomonas communis can complement an EF-P knockout in E. coli without requiring any PTM, suggesting they may represent new examples of unmodified EF-P. We also found that the EF-P from the Thermotogota Mesotoga prima is post-translationally modified in an off-target reaction by the rhamnosylation enzyme EarP, thus interfering with its functionality. Conversely, we saw that rhamnosylation by EarP does not impact the function of the EF-P-like protein EfpL.

Our findings highlight that PTM systems introduced via HGT can have varied effects on host proteins. We found that different EF-P variants are impacted in different ways by off-target rhamnosylation. While some of these off-target reactions may present opportunities to develop novel, catalytically active PTMs, others are detrimental to the function of the modified EF-P. Our results emphasize the complexity of gene integration and functional compatibility in foreign genomic contexts.