Phototrophy is an ancient bacterial metabolism that likely originated over 3 billion years ago, prior to the rise of atmospheric oxygen provoked by oxygenic photosynthesis of Cyanobacteriia. Phototrophy consists in the use of light for cellular energy production. This energy metabolism confers significant adaptive advantages to bacterial species in certain environments, yet it is sparsely distributed across several lineages of the bacterial tree of life. In the phylum Pseudomonadota (formerly Proteobacteria, also referred to as ‘purple bacteria’), phototrophy is also sparsely distributed across various clades, yet it was proposed in the 1980s by Carl Woese that the ancestor of Pseudomonadota was a phototroph. Thus the question of the evolutionary origins and transmission of phototrophy across Pseudomonadota still stands. The genetic potential for phototrophy is encoded by the photosynthetic gene cluster (PGC), a set of ~40 genes that colocalize in the genome and that gathers the genes required to produce photosynthetic pigments, as well as the reaction centers that are part of the light-harvesting antennae. Previous work by others found that the PGC could be found on plasmids, and a recent study suggested that the spread of phototrophy across the family Rhodobacteraceae was facilitated by horizontal gene transfer (HGT) of plasmids containing the PGC. The goal of the present study is to determine the respective contribution of vertical and lateral transmission of phototrophy in Pseudomonadota.To this end, an annotation tool based on the MacSyFinder program was designed for the annotation of PGC in bacterial genomes. More than 250 PGC were detected in 19 777 complete genomes of Pseudomonadota, which enabled subsequent phylogenomic analyses: genome context analyses and phylogenetic reconciliations between the PGC tree and the species tree. Overall, this study investigates the evolutionary history of phototrophy in Pseudomonadota and sets the grounds for a comparative genomic approach to investigate the metabolic factors underlying the sparse distribution of phototrophy across Pseudomonadota