Biodegradation of crude oil by Anabaena oryzae, Chlorella kessleri and its consortium under mixotrophic conditions

• This work highlights the ability of A. oryzae, C. kessleri and its consortium to grow under mixotrophic conditions at different concentrations of crude oil.
• Low light and/or nutrient deficiency encourage mixotrophy and these conditions commonly occur in the polluted environments.
• A. oryzae, C. kessleri and its consortium used in this study were able to degrade some hydrocarbons under mixotrophic conditions.
• The mixotrophic algae used in this study can offer new approach and more competitive advantages in the bioremediation efforts.
• An environmentally friendly and economically feasible method that can be used in large scale applications is described.

Oil spill occurs frequently all around the world which certainly impacts adversely the environment. Thus a low cost and environmentally friendly bioremediation could be an alternative way to solve the oil pollution problem. The present study presents a bioremediation attempt using the microalgae/cyanobacterium consortium of Anabaena oryzae and Chlorella kessleri. Each of A. oryzae and C. kessleri as well as its consortium could grow at different concentrations of crude oil (0.5, 1, and 1.5%) under mixotrophic conditions. However, 1% of crude oil was the optimum concentration for their maximum growth. Chlorophyll-a content of C. kessleri, A. oryzae and its consortium increased from the first day of incubation with 0.5 and 1% crude oil concentration up to 14 days. While, chlorophyll-b content of the consortium decreased at different concentration of crude oil after 14 days. The carotenoids content of A. oryzae and C. kessleri increased with increasing the oil concentration from 0.5 to 1% with increasing the incubation time until day seven. GC/MS analysis showed that some aliphatic compounds such as, 3-methyl-decane, heptadecane, octadecane, nonadecane, docosane and tetracosane completely disappeared when A. oryzae or C. kessleri was incubated mixotrophically with 1% crude oil. Aromatic compounds such as, naphthalene decahydro-2-methyl, benzene-decyl, cyclohexanebutyl- completely disappeared when the consortium was incubated mixotrophically with 1% crude oil for 30 days. Overall, our results indicate that C. kessleri, A. oryzae and its consortium can grow mixotrophically, and enhance the crude oil biodegradation.

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