Aerobic hydrocarbon-degrading Gammaproteobacteria – Porticoccus

The class Gammaproteobacteria contains the most important genera and largest diversity of obligate and generalist hydrocarbonoclastic bacteria that are found in the marine environment. With the exception of Planomicrobium alkanoclasticum (a Gram-positive of the Firmicutes), the class Gammaproteobacteria contains all known obligate hydrocarbonoclastic bacteria (OHCB), as represented by the genera Alcanivorax, Cycloclasticus, Neptunomonas, Oleibacter, Oleiphilus, Oleispira, and Thalassolituus. Prospecting studies aimed in identifying new taxa of hydrocarbonoclastic bacteria from underexplored biotopes in the ocean have uncovered novel OHCB within the Gammaproteobacteria, further increasing the known diversity of these organisms within this physiologically and phylogenetically diverse class. In this respect, one underexploited biotope is the cell surface, or phycosphere, of marine eukaryotic phytoplankton (micro-algae) as a source of OHCB. Members of the Alcanivorax and Marinobacter have been commonly reported living associated with many species of phytoplankton (diatoms, dinoflagellates, coccolithophores), and novel genera and species of OHCB (Polycyclovorans, Algiphilus, Porticoccus hydrocarbonoclasticus) have also been uncovered. This chapter discusses P. hydrocarbonoclasticus, which is a recently discovered OHCB that is not commonly represented in sequencing surveys, even from oil-polluted sites, and whose functional role in the water column and as a symbiont of phytoplankton remains to be resolved.