Abstract
BackgroundThe phosphoenolpyruvate phosphotransferase system (PTS) plays a major role in sugar transport and in the regulation of essential physiological processes in many bacteria. The PTS couples solute transport to its phosphorylation at the expense of phosphoenolpyruvate (PEP) and it consists of general cytoplasmic phosphoryl transfer proteins and specific enzyme II complexes which catalyze the uptake and phosphorylation of solutes. Previous studies have suggested that the evolution of the constituents of the enzyme II complexes has been driven largely by horizontal gene transfer whereas vertical inheritance has been prevalent in the general phosphoryl transfer proteins in some bacterial groups. The aim of this work is to test this hypothesis by studying the evolution of the phosphoryl transfer proteins of the PTS.ResultsWe have analyzed the evolutionary history of the PTS phosphoryl transfer chain (PTS-ptc) components in 222 complete genomes by combining phylogenetic methods and analysis of genomic context. Phylogenetic analyses alone were not conclusive for the deepest nodes but when complemented with analyses of genomic context and functional information, the main evolutionary trends of this system could be depicted.ConclusionThe PTS-ptc evolved in bacteria after the divergence of early lineages such as Aquificales, Thermotogales and Thermus/Deinococcus. The subsequent evolutionary history of the PTS-ptc varied in different bacterial lineages: vertical inheritance and lineage-specific gene losses mainly explain the current situation in Actinobacteria and Firmicutes whereas horizontal gene transfer (HGT) also played a major role in Proteobacteria. Most remarkably, we have identified a HGT event from Firmicutes or Fusobacteria to the last common ancestor of the Enterobacteriaceae, Pasteurellaceae, Shewanellaceae and Vibrionaceae. This transfer led to extensive changes in the metabolic and regulatory networks of these bacteria including the development of a novel carbon catabolite repression system. Hence, this example illustrates that HGT can drive major physiological modifications in bacteria.
Highlights
The phosphoenolpyruvate phosphotransferase system (PTS) plays a major role in sugar transport and in the regulation of essential physiological processes in many bacteria
Genetic organization and distribution of pts genes A total of 222 microbial genomes were screened for genes encoding enzyme I (EI), HPr or HPr kinase (HPrK)
The combination of TBLAST and PSI-BLAST searches allowed us to identify all genes and possible pseudogenes encoding the main components of the PTS phosphoryl transfer chain (PTS-ptc)
Summary
The phosphoenolpyruvate phosphotransferase system (PTS) plays a major role in sugar transport and in the regulation of essential physiological processes in many bacteria. The PTS couples solute transport to its phosphorylation at the expense of phosphoenolpyruvate (PEP) and it plays a central role in the regulation of a number of cell processes in some bacteria [3,4,5,6] This system consists of general cytoplasmic energy-coupling proteins, enzyme I (EI) and HPr, and specific enzyme II complexes, which catalyze the uptake and phosphorylation of solutes [3,7]. In Firmicutes, HPr can undergo a second ATP-dependent phosphorylation at a serine-46 residue, catalyzed by a metabolically activated HPr kinase (HPrK; see Fig. 1) [11,12] This ATP-dependent phosphorylation plays a major role in carbon catabolite repression (CCR) in these bacteria [13]. HPrK monomers are constituted by two structural domains: the carboxyl terminal domain displays the kinase and phosphorylase activities and responds to all known effectors as the entire enzyme [14] whereas the function of the N-terminal domain is unknown [15]
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