Interaction between cyanobacteria and aerobic heterotrophic bacteria in the degradation of hydrocarbons

Four strains of aerobic heterotrophic bacteria were isolated on crude oil with the aim to test whether their presence and activity might support the growth of cyanobacteria in oil-polluted microbial mats and whether the cyanobacterial exudates might play a role in stimulating their degradative activities. The strains were phylogenetically related to known oil-degrading species from the genera Marinobacter, Pseudomonas and Sphingomonas. Three strains (GM41, GM61 and GM63) grew well on C₅-C₁₈ alkanes but not on 7 tested aromatics, whereas one strain (i.e. GM42) grew best on phenanthrene and pentane. All strains showed ability to metabolize a range of cyanobacterial photosynthetic and fermentative exudates. In coculture experiments, the addition of the Pseudomonas-related GM41 strain to the cyanobacterium Synechocystis PCC6803, found in the same mat, resulted in 8-fold increase in the cyanobacterial biomass. This growth was more pronounced when hexadecane was added to the culture medium. The addition of representative substrates of cyanobacterial exudates to the phenanthrene-degrading strain GM42 resulted in variable effects. While acetate, pyruvate and glucose enhanced phenanthrene degradation, alanine and butanol showed no effect. We conclude that aerobic heterotrophic bacteria-cyanobacteria consortia can be very useful for bioremediating oil-polluted sites, circumventing the costly use of organic and inorganic fertilizers.