The genus Enterobacter comprises a range of beneficial plant-associated bacteria 2 showing plant growth-promotion. Enterobacter ludwigii belongs to the Enterobacter 3 cloacae complex and has been reported to include human pathogens but also plant-4 associated strains with plant beneficial capacities. To assess the role of Enterobacter 5 endophytes in hydrocarbon degradation, plant colonization, abundance and expression of 6 CYP153 genes in different plant compartments, three plant species (Italian ryegrass, 7 birdsfoot trefoil and alfalfa) were grown in sterile soil spiked with 1% diesel and 8 inoculated with three endophytic Enterobacter ludwigii strains. Results showed that all 9 strains were capable of hydrocarbon degradation and efficiently colonized the 10 rhizosphere and plant interior. Two strains, ISI10-3 and BRI10-9, showed highest 11 degradation rates of diesel fuel up to 68% and performed best in combination with Italian 12 ryegrass and alfalfa. All strains expressed the CYP153 gene in all plant compartments, 13 indicating an active role in degradation of diesel in association with plants.