Crude oil biodegradation by cyanobacteria from microbial mats: Fact or fallacy?

Microbial mats consist of multi-layered microbial communities organized in space as a result of steep physicochemical gradients. They can be found in sheltered and shallow coastal areas and intertidal zones where they flourish whenever extreme temperatures, dryness or saltiness act to exclude plants and animals. Several metabolically active microorganisms, such as phototrophs (i.e., diatoms, cyanobacteria, purple and green sulfur bacteria) develop in microbial mats together with chemoautotrophic and heterotrophic bacteria. These communities have been observed to grow in polluted sites where their ability to degrade petroleum components has been demonstrated. Furthermore, several investigations have attributed to cyanobacteria an important role in the biodegradation of organic pollutants. Nevertheless, it is still a matter of discussion whether cyanobacteria can develop using crude oil as the sole carbon source. In an attempt to evaluate their role in hydrocarbon degradation we have developed an illuminated packed tubular reactor filled with perlite soaked with crude oil inoculated with samples from Ebro Delta microbial mats. A continuous stream of nutrient-containing water was circulated through the system. Crude oil was the only carbon source and the reactor did not contain inorganic carbon. Oxygen tension was kept low in order to minimize possible growth of cyanobacteria at the expense of CO2 produced from the degradation of oil by heterotrophic bacteria. Different microorganisms were able to develop attached to the surface of the filling material, and analysis of microbial diversity within the reactor using culture-independent molecular techniques revealed the existence of complex assemblages of bacteria diverse both taxonomically and functionally, but cyanobacteria were not among them. However, cyanobacteria did grow in parallel oil-containing reactors in the presence of carbonate. © 2009 Nova Science Publishers, Inc. All rights reserved.