Abstract The human gut microbiota can acquire new catabolic functions by integrating genetic material coming from bacteria associated to the food. The most illustrative example is the acquisition of genes by the gut microbiota of Asian populations coming from marine bacteria living at the surface of algae incorporated in diet. In order to interrogate the pace of acquisition of algal polysaccharide utilizing loci (PUL) and their diffusion rate inside populations, we investigated the PUL dedicated to degradation of porphyran, the main polysaccharide of the red algae Porphyra sp . used to prepare maki-sushi. We demonstrated that both methylated and unmethylated fractions were catabolized without the help of external enzymes. The PUL organization was conserved in several Bacteroidetes strains, highlighting lateral transfers inside the microbiota, but we point out various conserved mutations, deletion and insertions. Geographic distribution of the variants showed that specific mutation and recombination events appeared independently in geographically distant populations.