BIODEGRADABILITY OF HYDROCARBONS BY CYANOBACTERIA 1 Ibraheem Borie Mohammad Ibraheem 2 Botany Department, Faculty of Science, Beni-Suef University, Beni-Suef 62511, Egypt Five cyanobacterial species (Phormidium sp., Nostoc sp., Anabaena sp. Aphanothece conferta, and Synecho- cystis aquatilis) isolated from the Suez Canal coast at the city of Ismailia (Egypt) were tested for biodegra- dation of four hydrocarbon (HC) compounds: two aliphatic compounds (n-octadecane and pristine) and two aromatic compounds (phenanthrene and dibenzothiophene). High degradation efficiencies for the two aliphatic compounds were measured for A. conferta (64% for n-octadecane and 78% for pris- tine) and S. aquatilis (85% for n-octadecane and 90% for pristane). However, the other biodegrada- tion percentages ranged between weak and moder- ate percentages. Key index words: Aphanothece conferta; biodegrada- tion of hydrocarbons; cyanobacteria; marine aquatic pollution; Suez Canal coast Abbreviations: BTMA, benzyl-trimethylammonium- chloride; DCM, dichloromethane; HC, hydrocar- bon; OCC, organo-clay complexes Pollution of marine environments with HCs has become a worldwide problem on the tide of indus- trialization. The sources of marine HC pollution are mainly runoff from land and municipal ⁄ industrial wastes, routine ship maintenance like bilge clean- ing, air pollution from cars and industry, natural seeps, tanker accidents, and offshore oil production (NRC 1985, U.S. Coast Guard 1990). It has long been known that poly-nuclear aromatic HCs exhibit serious toxic and carcinogenic effects (Miller and Miller 1974, McCann et al. 1975). Therefore, the study of the biotransformation and biodegradability of these aromatic compounds in the environment is of basic and particular value. The main process acting in the cleanup of HC- contaminated ecosystems is microbial biodegrada- tion, which has been extensively studied and reviewed (Atlas 1984, Leahy and Colwell 1990, Chai- llan et al. 2006). Numerous microorganisms, includ- ing bacteria, fungi, and yeasts, are known for their ability to degrade HCs (Oudot et al. 1993, Chaillan et al. 2004). In tropical crude oil production sites, cyanobacterial mats often develop on petroleum-pol- luted zones including surface soils and water envi- ronments. After the release of oil during the Gulf War in Kuwait, a bloom of cyanobacteria intimately associated with oil was also observed (Sorkhoh et al. 1992). There is increasing evidence that photosynthetic microorganisms, particularly cyanobacteria, may contribute to the oxidation and degradation of HCs. However, it is important to emphasize that only in some cases were the tested cyanobacterial cultures axenic and that many studies have been carried out on nonaxenic cultures. Among the earliest studies on the potential of photosynthetic microorganisms, including cyanobac- teria, for aromatic HC oxidation is the study of Ellis (1977). This author investigated the phenol and cat- echol degradation potential of some microalgae and cyanobacteria. Most of the work on aliphatic HCs has focused on the potential of these phototrophs for the complete utilization of these compounds. Previous reports have shown the ability of cyano- bacteria to oxidize oil components. Al-Hasan et al. (1998) reported that nonaxenic cultures of Microco- leus chthonoplastes and Phormidium corium, isolated from oil-rich sediments of the Arabian Gulf, were able to degrade n-alkanes. Studies on Oscillatoria sp. and Agmenellum quadruplicatum demonstrated their ability to oxidize naphthalene to 1-naphthol (Cerni- glia et al. 1980a). Other studies showed that Oscilla- toria sp. can oxidize biphenyl to n-hydroxybiphenyl (Cerniglia et al. 1980b) and that A. quadruplicatum metabolizes phenanthrene into trans-9,10-dihydroxy- 9,10-dihydrophenanthrene and 1-methoxy-phen- enthrene (Narro 1985). Several other strains were reported to degrade crude oil and other complex organic compounds (Lee et al. 1974, Cerniglia et al. 1984, Yan et al. 1998, Radwan and Al-Hasan 2000, Raghukumar et al. 2001, Mansy and El-Bestway 2002). However, in most biodegradation studies with cyanobacteria, it was not clear whether the strains used were definitively axenic (Abed and Ko ¨ster 2005). It is known to be very difficult to culti- vate cyanobacteria in axenic culture and to clean them from naturally associated aerobic heterotro- phic bacteria. Thus, the contribution of aerobic het- erotrophic bacteria associated with cyanobacteria to the biodegradation process needs to be carefully evaluated. In this study, I have addressed this 1 Received 17 November 2009. Accepted 19 April 2010. 2 Author for correspondence: e-mail ibraheemborie@hotmail.com. J. Phycol. 46, 818–824 (2010) Ó 2010 Phycological Society of America DOI: 10.1111/j.1529-8817.2010.00865.x 818