results obtained by the three methods reveal a correlation between biosurfactant production and emulsifying
activity.
Discussion
Crude oil contamination of ecosystems is a global environmental problem which oil-producing countries face
due to crude oil exploitation, refining, transportation,
storage as well as accidents. Numerous efforts have been
made to isolate indigenous oil-degrading bacteria in contaminated sediment and seawater in the Mediterranean
Sea especially in the northern side, while the southern
side remains poorly studied. Algeria is one of the top
three oil producers in Africa and its coasts have been
heavily contaminated over the past years, threatening
local ecosystems and human health. This study aims to
discern for the first time the intrinsic bioremediation
potential of a contaminated area (Sidi Fredj port) located
along the centre coast of Algeria (South Mediterranean
Sea)
Analysis of sediment samples from Sidi Fredj Port, by
the bioluminescence inhibition assay revealed that all sediment samples represented an acute toxicity. Sediment
from Station 3 was the most toxic. This may be due to
the presence of a fuel pump near station 3. There is a significant association between acute toxicity and the degree
of contamination with hydrocarbons (Schiewe et al.
1985). The bacterial diversity in seawater and sediment
samples collected from Sidi Fredj Port was performed by
the culture-independent technique DGGE. Results
showed that there is a higher diversity and variability in
seawater samples than in sediment samples (Catania et al.
2015). At the same time, seawater samples revealed higher
diversity of culturable hydrocarbon-degrading bacteria.
The most diverse seawater sample hosted higher total
bacterial diversity, higher abundance of bacteria and the
highest degree of bioluminescence inhibition from sediment samples of the same station.
The intrinsic biodegradability of the hydrocarbons and
the distribution in the environment of competent degrading micro-organisms are crucial information for the
implementation of bioremediation processes. In the present study, the search for micro-organisms with the
potential to use petroleum hydrocarbons was based on
their ability to grow in mineral medium containing
hydrocarbons as the only source of carbon and energy.
The hydrocarbon-degrading strains belonged to different
genera previously reported as oil-degrading species. Proteobacteria group represented nearly 83% of isolated
strains followed by Actinobacteria (13%) and Bacteroidetes (4%). Proteobacteria group is commonly found in
microbial communities exposed to hydrocarbon pollution
(McKew et al. 2007). Among the 23 strains selected,
Alcanivorax and Marinobacter were the most frequently
isolated. Bacteria closely related to Alcanivorax became
dominant in petroleum-contaminated seawater and are
considered as major actors in the bioremediation of oilcontaminated marine environments (Kasai et al. 2002;
Catania et al. 2015). These marine bacteria are well
known to use petroleum hydrocarbons as carbon and
energy source, and have been employed for bioremediation in polluted marine and coastal systems (Cappello
and Yakimov 2010). The dominance of these two genera
was also observed in the contaminated sediment of
Dalian Xingang Port (China) indicating the quick
response of Alcanivorax and Marinobacter to the hydrocarbons (Chen et al. 2017). Alcanivorax can use alkanes
as a sole carbon source (Harayama et al. 2004), and there
is evidence demonstrating that Marinobacter is responsible for the degradation of benzene, toluene, ethylbenzene,
xylene (BTEX) (Vila et al. 2010). Alkanes are the major
constituents of crude oil and the excellent ability of
Alcanivorax to degrade branched alkanes is one of the
factors that allow this strain to predominate in oil-contaminated seawater (Hara et al. 2003). Hydrocarbonoclastic bacteria such as Alcanivorax and Marinobacter are well
known for their ability to degrade hydrocarbons alone
with a high rate (Cappello et al. 2016) but a single species can metabolize only a limited range of hydrocarbon
substrates because it does not have all the enzymatic
machinery to degrade a pollutant until its complete mineralization (Mahjoubi et al. 2013). For this reason, a consortium of many different bacterial species, with broad
enzymatic capacities, is usually involved in oil degradation (R€ oling et al. 2002; De Pasquale et al. 2012). The
presence of Alcanivorax and Marinobacter in natural environments or enrichment by laboratory is generally combined with the presence of other bacterial strains (Santisi
et al. 2015). In this survey, other genera such as Pseudomonas, Erythrobacter, Gordonia, Halomonas and
Labrenzia were isolated. These strains cannot be classified
as hydrocarbonoclastic bacteria but are generalist hydrocarbon degraders. Erythrobacter and Labrenzia were determined as degraders of aromatic hydrocarbons (AlAwadhi et al. 2012; Gao et al. 2015), while Gordonia is
frequently reported to utilize aliphatic or aromatic compounds as growth substrate (Goodfellow and Maldonado
2006; Lo Piccolo et al. 2011).
Other Gram-positive strains belonging to micrococcaceae and brevibacteriaceae were isolated and are often
described in the literature as being isolated from hydrocarbon-contaminated environments (Chaillan et al. 2004;
Malik and Ahmed 2012). Even if the role of Gram-positive bacteria in hydrocarbon biodegradation is less
known, these organisms proved to be potential candidates
Journal of Applied Microbiology 126, 780--795 © 2018 The Society for Applied Microbiology
791
N. Djahnit et al.
The use of oil-degrading bacteria as an alternative for environmental remediation (bioremediation)
activity.
Discussion
Crude oil contamination of ecosystems is a global environmental problem which oil-producing countries face
due to crude oil exploitation, refining, transportation,
storage as well as accidents. Numerous efforts have been
made to isolate indigenous oil-degrading bacteria in contaminated sediment and seawater in the Mediterranean
Sea especially in the northern side, while the southern
side remains poorly studied. Algeria is one of the top
three oil producers in Africa and its coasts have been
heavily contaminated over the past years, threatening
local ecosystems and human health. This study aims to
discern for the first time the intrinsic bioremediation
potential of a contaminated area (Sidi Fredj port) located
along the centre coast of Algeria (South Mediterranean
Sea)
Analysis of sediment samples from Sidi Fredj Port, by
the bioluminescence inhibition assay revealed that all sediment samples represented an acute toxicity. Sediment
from Station 3 was the most toxic. This may be due to
the presence of a fuel pump near station 3. There is a significant association between acute toxicity and the degree
of contamination with hydrocarbons (Schiewe et al.
1985). The bacterial diversity in seawater and sediment
samples collected from Sidi Fredj Port was performed by
the culture-independent technique DGGE. Results
showed that there is a higher diversity and variability in
seawater samples than in sediment samples (Catania et al.
2015). At the same time, seawater samples revealed higher
diversity of culturable hydrocarbon-degrading bacteria.
The most diverse seawater sample hosted higher total
bacterial diversity, higher abundance of bacteria and the
highest degree of bioluminescence inhibition from sediment samples of the same station.
The intrinsic biodegradability of the hydrocarbons and
the distribution in the environment of competent degrading micro-organisms are crucial information for the
implementation of bioremediation processes. In the present study, the search for micro-organisms with the
potential to use petroleum hydrocarbons was based on
their ability to grow in mineral medium containing
hydrocarbons as the only source of carbon and energy.
The hydrocarbon-degrading strains belonged to different
genera previously reported as oil-degrading species. Proteobacteria group represented nearly 83% of isolated
strains followed by Actinobacteria (13%) and Bacteroidetes (4%). Proteobacteria group is commonly found in
microbial communities exposed to hydrocarbon pollution
(McKew et al. 2007). Among the 23 strains selected,
Alcanivorax and Marinobacter were the most frequently
isolated. Bacteria closely related to Alcanivorax became
dominant in petroleum-contaminated seawater and are
considered as major actors in the bioremediation of oilcontaminated marine environments (Kasai et al. 2002;
Catania et al. 2015). These marine bacteria are well
known to use petroleum hydrocarbons as carbon and
energy source, and have been employed for bioremediation in polluted marine and coastal systems (Cappello
and Yakimov 2010). The dominance of these two genera
was also observed in the contaminated sediment of
Dalian Xingang Port (China) indicating the quick
response of Alcanivorax and Marinobacter to the hydrocarbons (Chen et al. 2017). Alcanivorax can use alkanes
as a sole carbon source (Harayama et al. 2004), and there
is evidence demonstrating that Marinobacter is responsible for the degradation of benzene, toluene, ethylbenzene,
xylene (BTEX) (Vila et al. 2010). Alkanes are the major
constituents of crude oil and the excellent ability of
Alcanivorax to degrade branched alkanes is one of the
factors that allow this strain to predominate in oil-contaminated seawater (Hara et al. 2003). Hydrocarbonoclastic bacteria such as Alcanivorax and Marinobacter are well
known for their ability to degrade hydrocarbons alone
with a high rate (Cappello et al. 2016) but a single species can metabolize only a limited range of hydrocarbon
substrates because it does not have all the enzymatic
machinery to degrade a pollutant until its complete mineralization (Mahjoubi et al. 2013). For this reason, a consortium of many different bacterial species, with broad
enzymatic capacities, is usually involved in oil degradation (R€ oling et al. 2002; De Pasquale et al. 2012). The
presence of Alcanivorax and Marinobacter in natural environments or enrichment by laboratory is generally combined with the presence of other bacterial strains (Santisi
et al. 2015). In this survey, other genera such as Pseudomonas, Erythrobacter, Gordonia, Halomonas and
Labrenzia were isolated. These strains cannot be classified
as hydrocarbonoclastic bacteria but are generalist hydrocarbon degraders. Erythrobacter and Labrenzia were determined as degraders of aromatic hydrocarbons (AlAwadhi et al. 2012; Gao et al. 2015), while Gordonia is
frequently reported to utilize aliphatic or aromatic compounds as growth substrate (Goodfellow and Maldonado
2006; Lo Piccolo et al. 2011).
Other Gram-positive strains belonging to micrococcaceae and brevibacteriaceae were isolated and are often
described in the literature as being isolated from hydrocarbon-contaminated environments (Chaillan et al. 2004;
Malik and Ahmed 2012). Even if the role of Gram-positive bacteria in hydrocarbon biodegradation is less
known, these organisms proved to be potential candidates
Journal of Applied Microbiology 126, 780--795 © 2018 The Society for Applied Microbiology
791
N. Djahnit et al.
The use of oil-degrading bacteria as an alternative for environmental remediation (bioremediation)