Horizontal Gene Transfers Underpin Ribose Heterotrophy and Central Carbon Metabolism Remodeling in Gloeobacteraceae.

Gloeobacterales occupy a key phylogenetic position among cyanobacteria and are distinguished by the absence of thylakoid membranes. Using comparative genomics and phylogenetic analyses, we show that horizontal gene transfer has played a major role in shaping the central carbon metabolism of this lineage. In Gloeobacteraceae-one of the two families within the order-we identify a complete ribose ATP-synthase binding cassette importer and associated metabolic enzymes that enable ribose uptake and assimilation into central carbon metabolism alongside photosynthesis, indicative of a photomixotrophic lifestyle. Beyond ribose utilization, their central carbon metabolism exhibits a mosaic architecture shaped by the integration of foreign genes into the Calvin-Benson-Bassham cycle, the pentose phosphate pathway, and the Embden-Meyerhof-Parnas pathway. Uniquely, these genes appear to have been acquired through multiple independent transfer events, as reflected by their dispersed genomic locations and diverse bacterial donors, including other cyanobacteria and Pseudomonadota. These findings highlight Gloeobacterales as a dynamic lineage that continues to adapt and evolve through metabolic innovation and the assimilation of foreign genes into its genomes.