3.3 Degradation of Crude Oil
Another serious cause of environmental pollution that makes the soil and water
bodies unsuitable for plant growth and difficulty for the survival of aquatic organisms is crude oil. Furthermore, due to health-related problems associated with oil
spill, studies are directed toward finding a suitable solution to this problem. Bioremediation offers a better solution to treat oil spills due to its cost-effective nature.
Cyanobacteria are suitable candidates in bioremediation of crude oil due to their
ability of growing under various conditions and forming bloom with other organisms. Naphthalene, a main constituent of water-soluble part of crude oil, was
reported to have been degraded by the cyanobacteria Oscillatoria sp. strain JCM
(Narro et al. 1992). The cyanobacteria species Oscillatoria salina, Aphanocapsa sp.,
and Plectonema terenbans were also found to degrade crude oil (Raghukumar et al.
2001). Within 10 days, 50–65% of pure hexadecane, 45–55% of total crude oil
fractions, and 20–90% of aromatic compound were removed. After forming a
cyanobacterial mat by the mixed culture of the three cyanobacterial species, about
40% of the crude oil was removed. Phormidium corium and Microcoleus
chthonoplastes species of cyanobacteria also degraded crude oil by consuming the
individual n-alkanes (Al Hasan et al. 1994). When the growth was measured in terms
of biliprotein content and dry biomass, the two species grew better in crude oil
suggesting the utilization of these hydrocarbons.
Contrary to the above studies, other investigations revealed that cyanobacteria are
not directly involved in the degradation of petroleum compound but rather play a
major role by enhancing the activity and growth of the actual degraders. For
example, Abed and Köster (2005) concluded that the aerobic heterotrophic bacteria
associated with the cyanobacteria were responsible for the degradation of oil compounds and not the cyanobacteria. Oil-degrading consortium was also analyzed
using 16S rRNA (Sa’nchez et al. 2005). The organisms obtained were found to be
related to agrobacterium and rhizobium nitrogen-fixing bacteria. The result indicates
that the heterotrophic bacteria associated with cyanobacteria are the ones responsible
for degradation of the hydrocarbon, while the cyanobacteria provide oxygen, organic
matter, and habitat for the heterotrophic bacteria. The same conclusion was made by
Radwan et al. (2002) and Sa’nchez et al. (2005). While the actual degraders degrade
the hydrocarbon, the cyanobacteria provide fixed nitrogen and simple organic
compound and oxygen for the breakdown of aromatic rings (Abed and Köster
2005) which are also necessary for the growth and the activity of the actual
degraders. The evidences for degrading and not degrading hydrocarbon by
cyanobacteria are tentative; however, Radwan and Al- Hasan (2002) concluded
that some species/strains are capable of utilizing aliphatic and aromatic compounds,
while others that occur together with other natural hydrocarbon-degrading bacteria
forming cyanobacterial mat only enhance the growth and activities of the degrading
bacteria. The association between the two appeared to be significant and crucial in
remediation of crude oil.
402
S. Mona et al.
Another serious cause of environmental pollution that makes the soil and water
bodies unsuitable for plant growth and difficulty for the survival of aquatic organisms is crude oil. Furthermore, due to health-related problems associated with oil
spill, studies are directed toward finding a suitable solution to this problem. Bioremediation offers a better solution to treat oil spills due to its cost-effective nature.
Cyanobacteria are suitable candidates in bioremediation of crude oil due to their
ability of growing under various conditions and forming bloom with other organisms. Naphthalene, a main constituent of water-soluble part of crude oil, was
reported to have been degraded by the cyanobacteria Oscillatoria sp. strain JCM
(Narro et al. 1992). The cyanobacteria species Oscillatoria salina, Aphanocapsa sp.,
and Plectonema terenbans were also found to degrade crude oil (Raghukumar et al.
2001). Within 10 days, 50–65% of pure hexadecane, 45–55% of total crude oil
fractions, and 20–90% of aromatic compound were removed. After forming a
cyanobacterial mat by the mixed culture of the three cyanobacterial species, about
40% of the crude oil was removed. Phormidium corium and Microcoleus
chthonoplastes species of cyanobacteria also degraded crude oil by consuming the
individual n-alkanes (Al Hasan et al. 1994). When the growth was measured in terms
of biliprotein content and dry biomass, the two species grew better in crude oil
suggesting the utilization of these hydrocarbons.
Contrary to the above studies, other investigations revealed that cyanobacteria are
not directly involved in the degradation of petroleum compound but rather play a
major role by enhancing the activity and growth of the actual degraders. For
example, Abed and Köster (2005) concluded that the aerobic heterotrophic bacteria
associated with the cyanobacteria were responsible for the degradation of oil compounds and not the cyanobacteria. Oil-degrading consortium was also analyzed
using 16S rRNA (Sa’nchez et al. 2005). The organisms obtained were found to be
related to agrobacterium and rhizobium nitrogen-fixing bacteria. The result indicates
that the heterotrophic bacteria associated with cyanobacteria are the ones responsible
for degradation of the hydrocarbon, while the cyanobacteria provide oxygen, organic
matter, and habitat for the heterotrophic bacteria. The same conclusion was made by
Radwan et al. (2002) and Sa’nchez et al. (2005). While the actual degraders degrade
the hydrocarbon, the cyanobacteria provide fixed nitrogen and simple organic
compound and oxygen for the breakdown of aromatic rings (Abed and Köster
2005) which are also necessary for the growth and the activity of the actual
degraders. The evidences for degrading and not degrading hydrocarbon by
cyanobacteria are tentative; however, Radwan and Al- Hasan (2002) concluded
that some species/strains are capable of utilizing aliphatic and aromatic compounds,
while others that occur together with other natural hydrocarbon-degrading bacteria
forming cyanobacterial mat only enhance the growth and activities of the degrading
bacteria. The association between the two appeared to be significant and crucial in
remediation of crude oil.
402
S. Mona et al.