Environmental Microbiology of Aquatic and Waste Systems

7.3 Pollution by Petroleum in Oceans and Seas: Role of Microorganisms in Oil Degradation and Remediation 183

(b) The physical state of the oil
The degree of the dispersion of the oil is impor-
tant in deciding the rate of microbial break-
down; the more dispersed the oil the faster the
rate of microbial breakdown because of the
greater contact with the microorganisms.
(c) Environmental factors
The environmental factors affecting microbial
breakdown include the temperature, the avail-
ability of oxygen, and the nutrients available in
the water.
(d) The nature and numbers of the oil-degrading
microorganisms in the water
The species, composition and abundance of oil-
degrading microorganisms in the water is impor-
tant in deciding the rate of oil breakdown. Complex
and interconnected factors influence biodegrada-
tion in the marine environment. These factors will
be examined in a little more detail below.
(e) Biodegradation of oil
Of all the various factors, which affect the
weathering or disappearance of oil, microbial
degradation is the most important.
Microorganisms, especially bacteria, defi-
nitely play a part in the breakdown of oil. Many
isolations have been made from oil and water of
microorganisms capable of using crude oil as
the only source of carbon. Table 7.12 shows the
bacteria (including cyanobacteria), algae, and
fungi, which can degrade oil and oil components
(Raghukumar et al. 2001 ). Microbes degrading
oil usually account for less than 1% of natural
populations of microbes, but can account for
more than 10% of the population in waters pol-
luted with oil. Obligate hydrocarbon-degrading
bacteria, designated as “hydrocarbonoclastic”
and belonging to genera in the gamma-
proteobacteria, are isolated regularly in marine
water when an oil spill has occurred. Crude oil
is a complex mixture of different hydrocarbons,
and different bacteria have been shown to attack
specific components of oil (Leahy and Colwell
1990 ). In one study, for instance, the degrada-
tion of PAHs (polycyclic aromatic hydrocar-
bons) was shown to be carried out mainly by
Cycloclasticus. PAHs are chemical compounds
that consist of fused aromatic rings and do not
carry substituents. PAHs occur in oil, coal, and
tar deposits, and are believed to be carcinogenic.

On the other hand, the degradation of the

branched alkane, pristane, was carried out

almost exclusively by Alcanivorax. Bacteria

related to Thalassolituus oleivorans were the

dominant degraders in n-alkane (C12–C32).

The marine bacterium, Roseobacter, was pres-

ent among the various groups but was not domi-

nant. Figure 7.7 shows the pathways for the

breakdown of some oil components. Table 7.12

shows a list of microorganisms degrading oil.

7.3.2.2 Remediation of Oil Spills

Remediation and cleanup techniques for oil spills

depend largely on the type of oil and the conditions

Table 7.12 Bacteria and fungi degrading oil (Modified from

Gordon 1994 ; Raghukumar et al. 2001 )

Bacteria Fungi

Achromobbacter Allescheria

Acinetobacter Aspergillus

Actinomyces Aureobasidium

Aeromonas Botrytis

Alcaligenes Candida

Arthrobacter Cephaiosporium

Bacillus Cladosporium

Beneckea Cunninghamella

Brevebacterium Debaromyces

Coryneforms Fusarium

Erwinia Gonytrichum

Flavobacterium Hansenula

Klebsiella Helminthosporium

Lactobacillus Mucor

Leucothrix Oidiodendrum

Moraxella Paecylomyces

Nocardia Phialophora

Peptococcus Penicillium

Pseudomonas Rhodosporidium

Sarcina Rhodotorula

Spherotilus Saccharomyces

Spirillum Saccharomycopisis

Streptomyces Scopulariopsis

Vibrio Sporobolomyces

Xanthomyces Torulopsis

Oscillatoria

Plectonema

Trichoderma

Aphanocapsa Trichosporon

Thalassolituus

Alcanivorax

Cycloclasticus

Note: The last six in the column for bacteria are Cyanobacteria