Aerobic Hydrocarbon-Degrading Gammaproteobacteria: Xanthomonadales

The Xanthomonadales comprises a morphologically and physiologically diverse order of bacteria, though its classification has been contentious pertaining to its division into families. Currently, the order is divided into the two families, Xanthomonadaceae and Rhodanobacteraceae, that collectively contain members from approximately 29 genera. Hydrocarbon degraders of the family Xanthomonadaceae include members of the genera Arenimonas, Luteimonas, Pseudoxanthomonas, Stenotrophomonas, Xanthomonas, and Xylella, whereas those of the family Rhodanobacteraceae include Dokdonella, Dyella, Frateuria, Luteibacter, Oleiagrimonas, Rhodanobacter, and Rudaea. These organisms are categorized as generalist hydrocarbon-degraders based on their ability to also utilize various other carbon substrates as a sole source of carbon and energy. To-date, of the nine recognized genera of obligate hydrocarbonoclastic bacteria that are able to degrade hydrocarbons almost exclusively as a preferred carbon and energy source, only Algiphilus and Polycyclovorans are represented within the order Xanthomonadales, principally within the family Xanthomonadaceae. The type species of these two genera are Algiphilus aromaticivorans and Polycyclovorans algicola, which respectively were originally isolated from the phycosphere of a marine dinoflagellate and diatom. Members of these two genera have also been identified living associated with various other species of marine eukaryotic phytoplankton, and sequencing surveys have identified their presence in a wide variety of environments that include oil-contaminated and noncontaminated marine and terrestrial environments as well as human skin.