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

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 affects the compatibility and consequences of acquiring post-translational modification (PTM) machinery through HGT using the heterologous expression of the highly conserved translational elongation factor P (EF-P) from diverse species in Escherichia coli as a model. EF-P and its PTM machinery have been horizontally transferred many times across the bacterial tree of life, and these experiments are meant to examine the consequences of these events. EF-P has a diverse and heterogenous relationship with PTMs; three characterized variants each undergo distinct PTM pathways, while others function effectively without any modification. In this study, we demonstrate that EF-P from Deinococcus radiodurans , Geoalkalibacter ferrihydriticus , and Nitrosomonas communis can complement an EF-P knockout in E. coli without requiring modification, suggesting they represent new examples of unmodified EF-Ps. 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 is fully compatible with the EF-P-like protein EfpL from Escherichia coli , thus presenting a promising opportunity to develop novel, catalytically active PTMs. These findings highlight that PTM systems introduced via HGT can have unintended effects on host proteins, emphasizing the complexity of gene integration and functional compatibility in foreign genomic contexts.