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International Journal of Marine Science, 2017, Vol.7, No.18, 176-182
181
Figure 18 Crude oil 2.0% with
V.vulnificus
Figure 19 Crude oil 2.0% with
Brev.dimi./vesicu
Figure 20 Crude oil 2.0% with
Sphmon.paucimobilis
3 Discussion
The microorganisms which have the ability to degrade crude oil and use it as a sole carbon source are widely
distributed in air, water and soil (Bello, 2007; Al-Sulami et al., 2014). Four genera have been identified as
Vibrio
vulnificus; Brevundimonas diminuta/vesicularis; Ochrobactrum anthropic
and
Sphingomonas paucimobilis
from
brackish water in Khor Al-Zubair, southern Iraq, using the VITEK II system. The VITEK II direct identification
testing of gram negative bacilli had a correct identification rate of 86.15%, none of the results gave a wrong
identification and nine (13.84%) were not identified. These bacteria have been participating in the process of
crude oil degradation and exploited it as a source of carbon and energy, according to Kosaric (2000) three models
of hydrocarbon transport of bacterial cells are considered, either by interaction of cells with more water soluble
hydrocarbons, or by the direct touch of cells with big drops of hydrocarbon. During this process bacterial cells
attach to the surface of hydrocarbon drops that are too bigger than cells; the substrate surface area availability for
cell attachment is a limiting factor; production of biosurfactant by hydrocarbon utilizing bacteria cause the
dispersion of hydrocarbon droplets in the aqueous environment and that way leads to increasing the surface area.
And bacterial cells interact with particles of solubilized, microemulisifeid hydrocarbons. So, according to the type
of organism, hydrocarbon uptake/degradation may occur in one of these mechanisms (Prabhu and Phale, 2003).
The action of these mechanisms may include alteration in cell physiology, which will cause either to changes in
the properties of cell surface as hydrophobicity or secretion compounds into the medium or a combination of both
(Plaza et al., 2005). The results indicate that, these bacteria have the ability to attack all the hydrocarbon chains
within seven days. Despite the fact that, many studies find, the microorganisms attack first, lower and higher
hydrocarbon chains and those of middle length were attacked later in the course of incubation (Bello, 2007; Malik
and Ahmed, 2012; Al-Sulami et al., 2014).
In the present study, four concentrations of crude oil were studied in liquid medium by axenic culture of four
different genera. The results of gas chromatography showed that, there are fluctuations in the ability of bacteria to
degrade crude oil (Table 2), but the isolates of
V. vulnificus
was the most effective strain has the ability to degrade
crude oil, which reached 93.05% in concentration 2%, while
Ochrobactrum anthropi
was the lowest 9.63% in
concentration 0.25%.
