affected in different degrees by pesticides. The most affected
biological process of using pesticides is the symbiotic
nitrogen fixation process. Quantitative effects of Temik
(insecticide and nematocide), Orthocide (fungicide), or
Treflan (herbicide) were tested on soil microorganisms. The
effect of any pesticide on counts of Azotobacter, N-fixing
Clostridia, and ammonifiers was subsequently depressive.
However, the autotrophic nitrifying bacteria, especially
ammonium oxidizers, seemed to be more sensitive, and their
counts in treated soil were sharply depressed (Makawi et al.,
1979). Zaid et al. (2014) found that Terbutryn, Propyzamide,
and Propyzamide had no significant effect on nitrogen-fixing
bacteria, except in the case of carbetamide, which increased
the total number of nodules per plant. Actinomycetes were
reduced by all herbicides treatments, but the total number of
soil fungi increased by using Propyzamide and Metribuzin.
In other cases, Elssaidi and Mohamed (2015) found that
Rhizobium bacteria that isolated from fenugreek, R. meliloti,
was the most affected and sensitive species for pesticides.
Additionally, not all the rates of pesticides application were
effective, and, in the short term, no harmful effects were
observed. However, bioaccumulation, in the long term, may
lead to chronic toxicity. Another study revealed that the use
of pesticides led to a decrease in numbers of Nitrosomonas,
Nitrobacter, and cellulose-decomposing bacteria at the recommended concentrations and dose. Also, there was a
highly significant interaction between the type of insecticide
and its concentration (Al Hammadi 2015). Using fungicide
(Benomyl 50%) and insecticide (Abamectin) had a different
effect on the growth of nitrogen fixing bacteria Azotobacter
and Burkholderia, depending on the concentrations and
incubation periods. Azotobacter and Burkholderia, with the
dilution of 10
−4
, were more tolerant of pesticides as compared with other dilutions of 10
−5 and 10
−6 (Ben Mahmoud
and Ferjani 2017).
The bottom line of these studies is that pesticides can
have an inhibitory or stimulating effect on microorganisms
in soils, and the period of retardation or stimulation is different according to the chemical composition, the concentration of the pesticides, and the physiological properties of
micro-organisms.
7.6 Bioremediation of Crude Oil
Interest in bioremediation field has increased in recent years,
and many studies have shown that microorganisms have the
potential to be used for the clean-up of sites contaminated by
crude oil. Hesnawi and Mogadami (2013) revealed that
mesophilic bacteria was more beneficial for biodegradation
than thermophilic. The observed total petroleum hydrocarbons (TPHs) removal was 79.8 and 62.4% at mesophilic and
thermophilic temperatures, respectively.
A scale study by Shaieb et al. (2015) indicated that four
bacterial isolates from the Libyan desert were identified as
Cellulosimicrobium cellulans, Brevibacterium liquefaciens,
Enterococcus saccharolyticus, and Brevibacterium mcbrellneri. The concentration of the TPHs in the cultures of the
selected isolates was decreased to 18.86, 26.16 and 39.04%
for the first three genera, respectively. The bacteria isolates
have the potential to be used in the bioremediation of crude
oil. El Mahdi et al. (2015) revealed that 20 crude oildegrading bacterial strains were isolated from
oil-contaminated sites at Al Hariga Oil Terminal and
Nafoora Oil Field. Two isolates were identified by 16S
rDNA gene sequence analysis to be Pseudomonas aeruginosa NAF1 and Kocuria pastrius SAR3. P. aeruginosa
NAF1 exhibited 70 and 76% crude oil degradation. Likewise, K. pastrius SAR3 expressed 68 and 70% crude oil
degradation in batches supplemented with 0.2% corn steep
liquor (CSL) and solid waste date (SWD) within 28 days.
The degradation efficiency of P. aeruginosa NAF1 also
increased to reach 91 and 97% using 0.5% (w/v) (CSL) and
(SWD), respectively.
The oil industry generates massive amounts of crude oil
tank bottom sludge (COTBS), a complex mixture of hydrocarbons. COTBS contains a significant amount of recoverable oil (42.08%). Hydrocarbonclastic bacteria were isolated
from COTBS and characterized in terms of their hydrocarbonoclastic potential. Three bacterial isolates (Pseudomonas
sp., Pseudomonas xanthomarina, and Arthrobacter
nitroguajacolicus) were used in microcosm slurry phase
bioremediation trials. After 30 days, the degradation rate
ranged from 97.8 to 99.4%, where the total TPH concentration was reduced from 30,703 to (170–664) mg kg
−1 . In
addition, the complete biodegradation of the carcinogenic
and mutagenic fractions occurred. The research suggests that
this sustainable remediation technology can be used as a
substitute for the currently used physical and chemical
treatment methods applied in Libya (Mansur 2015).
In another study, Mansur et al. (2015) attempt to develop
a slurry phase bioremediation protocol. Two hydrocarbonoclastic bacterial isolates, Pseudomonas spp. and Pseudomonas xanthomarina, were used in three different
strategies, namely: bioaugmentation (BA), biostimulation
(BS), and biostimulation-bioaugmentation (BS-BA), to
assess their ability to reduce the TPHs in COBTS contaminated soil. The results indicated that the BS–BA treatments
showed the highest reduction (96–97%, from 30,703 to
(860–1020) mg kg
−1 ), followed by the BS treatment (92–
93% reduction).
BS–BA treatments are used to assess their ability to
reduce the TPHs in COBTS contaminated soil. The results
indicated that the BS-BA treatments showed the highest
reduction (96–97%, from 30,703 to (860–1020) mg kg
−1 ),
followed by the BS treatment (92–93% reduction).
7 Soil Microbiology and Biotechnology
115
biological process of using pesticides is the symbiotic
nitrogen fixation process. Quantitative effects of Temik
(insecticide and nematocide), Orthocide (fungicide), or
Treflan (herbicide) were tested on soil microorganisms. The
effect of any pesticide on counts of Azotobacter, N-fixing
Clostridia, and ammonifiers was subsequently depressive.
However, the autotrophic nitrifying bacteria, especially
ammonium oxidizers, seemed to be more sensitive, and their
counts in treated soil were sharply depressed (Makawi et al.,
1979). Zaid et al. (2014) found that Terbutryn, Propyzamide,
and Propyzamide had no significant effect on nitrogen-fixing
bacteria, except in the case of carbetamide, which increased
the total number of nodules per plant. Actinomycetes were
reduced by all herbicides treatments, but the total number of
soil fungi increased by using Propyzamide and Metribuzin.
In other cases, Elssaidi and Mohamed (2015) found that
Rhizobium bacteria that isolated from fenugreek, R. meliloti,
was the most affected and sensitive species for pesticides.
Additionally, not all the rates of pesticides application were
effective, and, in the short term, no harmful effects were
observed. However, bioaccumulation, in the long term, may
lead to chronic toxicity. Another study revealed that the use
of pesticides led to a decrease in numbers of Nitrosomonas,
Nitrobacter, and cellulose-decomposing bacteria at the recommended concentrations and dose. Also, there was a
highly significant interaction between the type of insecticide
and its concentration (Al Hammadi 2015). Using fungicide
(Benomyl 50%) and insecticide (Abamectin) had a different
effect on the growth of nitrogen fixing bacteria Azotobacter
and Burkholderia, depending on the concentrations and
incubation periods. Azotobacter and Burkholderia, with the
dilution of 10
−4
, were more tolerant of pesticides as compared with other dilutions of 10
−5 and 10
−6 (Ben Mahmoud
and Ferjani 2017).
The bottom line of these studies is that pesticides can
have an inhibitory or stimulating effect on microorganisms
in soils, and the period of retardation or stimulation is different according to the chemical composition, the concentration of the pesticides, and the physiological properties of
micro-organisms.
7.6 Bioremediation of Crude Oil
Interest in bioremediation field has increased in recent years,
and many studies have shown that microorganisms have the
potential to be used for the clean-up of sites contaminated by
crude oil. Hesnawi and Mogadami (2013) revealed that
mesophilic bacteria was more beneficial for biodegradation
than thermophilic. The observed total petroleum hydrocarbons (TPHs) removal was 79.8 and 62.4% at mesophilic and
thermophilic temperatures, respectively.
A scale study by Shaieb et al. (2015) indicated that four
bacterial isolates from the Libyan desert were identified as
Cellulosimicrobium cellulans, Brevibacterium liquefaciens,
Enterococcus saccharolyticus, and Brevibacterium mcbrellneri. The concentration of the TPHs in the cultures of the
selected isolates was decreased to 18.86, 26.16 and 39.04%
for the first three genera, respectively. The bacteria isolates
have the potential to be used in the bioremediation of crude
oil. El Mahdi et al. (2015) revealed that 20 crude oildegrading bacterial strains were isolated from
oil-contaminated sites at Al Hariga Oil Terminal and
Nafoora Oil Field. Two isolates were identified by 16S
rDNA gene sequence analysis to be Pseudomonas aeruginosa NAF1 and Kocuria pastrius SAR3. P. aeruginosa
NAF1 exhibited 70 and 76% crude oil degradation. Likewise, K. pastrius SAR3 expressed 68 and 70% crude oil
degradation in batches supplemented with 0.2% corn steep
liquor (CSL) and solid waste date (SWD) within 28 days.
The degradation efficiency of P. aeruginosa NAF1 also
increased to reach 91 and 97% using 0.5% (w/v) (CSL) and
(SWD), respectively.
The oil industry generates massive amounts of crude oil
tank bottom sludge (COTBS), a complex mixture of hydrocarbons. COTBS contains a significant amount of recoverable oil (42.08%). Hydrocarbonclastic bacteria were isolated
from COTBS and characterized in terms of their hydrocarbonoclastic potential. Three bacterial isolates (Pseudomonas
sp., Pseudomonas xanthomarina, and Arthrobacter
nitroguajacolicus) were used in microcosm slurry phase
bioremediation trials. After 30 days, the degradation rate
ranged from 97.8 to 99.4%, where the total TPH concentration was reduced from 30,703 to (170–664) mg kg
−1 . In
addition, the complete biodegradation of the carcinogenic
and mutagenic fractions occurred. The research suggests that
this sustainable remediation technology can be used as a
substitute for the currently used physical and chemical
treatment methods applied in Libya (Mansur 2015).
In another study, Mansur et al. (2015) attempt to develop
a slurry phase bioremediation protocol. Two hydrocarbonoclastic bacterial isolates, Pseudomonas spp. and Pseudomonas xanthomarina, were used in three different
strategies, namely: bioaugmentation (BA), biostimulation
(BS), and biostimulation-bioaugmentation (BS-BA), to
assess their ability to reduce the TPHs in COBTS contaminated soil. The results indicated that the BS–BA treatments
showed the highest reduction (96–97%, from 30,703 to
(860–1020) mg kg
−1 ), followed by the BS treatment (92–
93% reduction).
BS–BA treatments are used to assess their ability to
reduce the TPHs in COBTS contaminated soil. The results
indicated that the BS-BA treatments showed the highest
reduction (96–97%, from 30,703 to (860–1020) mg kg
−1 ),
followed by the BS treatment (92–93% reduction).
7 Soil Microbiology and Biotechnology
115