12.66–40.54% after 168 h. Besides, Kabra et al. (2014) studied the ability of green
microalgae Chlamydomonas mexicana to degrade atrazine and found that
microalgae accumulate atrazine in cells and then degrading it effectively, reaching
a degradation rate of 14–36%. Another popular herbicide 2,4-dichlorophenoxyacetic
acid (2,4-D) is used in many crops around the world in various crops such as wheat,
rice, corn, sorghum, and sugarcane. World Health Organization has classified this
herbicide as a carcinogen agent of level II toxicity. However, some microbial
species, such as Acinetobacter spp., Serratia marcescens, Stenotrophomonas
maltophilia, Flavobacterium spp., and Penicillium spp., have been reported to be
rapidly consistent with the presence of 2,4-D, with subsequent degradation under
in vitro conditions (Silva et al. 2011).
Polycyclic aromatic hydrocarbons (PAH), a class of hazardous chemicals
containing two or more fused benzene rings in various structural configurations,
are listed as priority pollutants by the U.S. Environmental Protection Agency due to
their carcinogenic, mutagenic, and toxic effects (Poonthrigpun et al. 2006). Ahmad
et al. (1997) characterized Rhizobium meliloti strains in soils contaminated with
aromatic/chloroaromatic hydrocarbons. The rhizobial population was composed of
many phenotypic and genetically diverse strains, and all rhizobial cells are effective
in symbiotic N 2 fixation. Another group of ubiquitous PAHs in the environment
includes acenaphthylene and phenanthrene. Acenaphthylene can be completely
degraded by Rhizobium spp. strain CU-A1 in 3 days by the metabolic pathway of
naphthalene-1,8-dicarboxylic acid (Poonthrigpun et al. 2006). On the other hand,
Sinorhizobium spp. C4 was found to use phenanthrene as a single carbon source, and
16 intermediate metabolites involved in this degradation pathway were identified
(Keum et al. 2006). Some toxic aromatic acids as well as hydrodynamic biosynthetic
intermediates (i.e., quinate and shikimate) commonly found in plants and in the
rhizosphere contribute to the growth of different rhizobial species (Parke et al. 1985).
Many free-living rhizobial strains of the genus Agrobacterium, Bradyrizobium,
Rhizobium, and Sinorhizobium have demonstrated the utilization of PAHs, PCBs,
aromatic heterocycles (i.e., pyridine), or other toxic organic compounds
(Poonthrigpun et al. 2006; Tu et al. 2011).
Polychlorinated biphenyls (PCBs) are another class of POPs that differ in the
number of chlorine atoms attached to their biphenyl rings (Passatore et al. 2014). Tu
et al. (2011) demonstrated that Sinorhizobium meliloti strain ACCC17519 degraded
more than 70% of 2,4,4
0 -TCB (PCB28) compared to other rhizobial strains. Aromatic toxin produced by the sources of mimosine, Leucaena sp. is toxic to both
bacteria and eukaryotic cells (Awaya et al. 2005). Some Leucaena-nodulating
Rhizobium strains have been reported to utilize mimosine as a source of carbon
and nitrogen (Soedarjo et al. 1995; Soedarjo and Borthakur 1998), indicating the
catalytic ability of rhizobia to use aromatic compounds. Strains of R. meliloti could
utilize 2,4,4
0 -TCB (PCB28) as a sole carbon and energy source under aerobic
conditions, and HOPDA has been identified as a major intermediate during the
biotransformation of 2,4,4-TCB by S. meliloti (Xu et al. 2010; Tu et al. 2011).
Chlorpyrifos is one of the most widely used insecticides to control mosquitoes
(larvae and adults), flies, and various soil, leaf crop, and household pests. Klebsiella
38
A. Sehrawat et al.
microalgae Chlamydomonas mexicana to degrade atrazine and found that
microalgae accumulate atrazine in cells and then degrading it effectively, reaching
a degradation rate of 14–36%. Another popular herbicide 2,4-dichlorophenoxyacetic
acid (2,4-D) is used in many crops around the world in various crops such as wheat,
rice, corn, sorghum, and sugarcane. World Health Organization has classified this
herbicide as a carcinogen agent of level II toxicity. However, some microbial
species, such as Acinetobacter spp., Serratia marcescens, Stenotrophomonas
maltophilia, Flavobacterium spp., and Penicillium spp., have been reported to be
rapidly consistent with the presence of 2,4-D, with subsequent degradation under
in vitro conditions (Silva et al. 2011).
Polycyclic aromatic hydrocarbons (PAH), a class of hazardous chemicals
containing two or more fused benzene rings in various structural configurations,
are listed as priority pollutants by the U.S. Environmental Protection Agency due to
their carcinogenic, mutagenic, and toxic effects (Poonthrigpun et al. 2006). Ahmad
et al. (1997) characterized Rhizobium meliloti strains in soils contaminated with
aromatic/chloroaromatic hydrocarbons. The rhizobial population was composed of
many phenotypic and genetically diverse strains, and all rhizobial cells are effective
in symbiotic N 2 fixation. Another group of ubiquitous PAHs in the environment
includes acenaphthylene and phenanthrene. Acenaphthylene can be completely
degraded by Rhizobium spp. strain CU-A1 in 3 days by the metabolic pathway of
naphthalene-1,8-dicarboxylic acid (Poonthrigpun et al. 2006). On the other hand,
Sinorhizobium spp. C4 was found to use phenanthrene as a single carbon source, and
16 intermediate metabolites involved in this degradation pathway were identified
(Keum et al. 2006). Some toxic aromatic acids as well as hydrodynamic biosynthetic
intermediates (i.e., quinate and shikimate) commonly found in plants and in the
rhizosphere contribute to the growth of different rhizobial species (Parke et al. 1985).
Many free-living rhizobial strains of the genus Agrobacterium, Bradyrizobium,
Rhizobium, and Sinorhizobium have demonstrated the utilization of PAHs, PCBs,
aromatic heterocycles (i.e., pyridine), or other toxic organic compounds
(Poonthrigpun et al. 2006; Tu et al. 2011).
Polychlorinated biphenyls (PCBs) are another class of POPs that differ in the
number of chlorine atoms attached to their biphenyl rings (Passatore et al. 2014). Tu
et al. (2011) demonstrated that Sinorhizobium meliloti strain ACCC17519 degraded
more than 70% of 2,4,4
0 -TCB (PCB28) compared to other rhizobial strains. Aromatic toxin produced by the sources of mimosine, Leucaena sp. is toxic to both
bacteria and eukaryotic cells (Awaya et al. 2005). Some Leucaena-nodulating
Rhizobium strains have been reported to utilize mimosine as a source of carbon
and nitrogen (Soedarjo et al. 1995; Soedarjo and Borthakur 1998), indicating the
catalytic ability of rhizobia to use aromatic compounds. Strains of R. meliloti could
utilize 2,4,4
0 -TCB (PCB28) as a sole carbon and energy source under aerobic
conditions, and HOPDA has been identified as a major intermediate during the
biotransformation of 2,4,4-TCB by S. meliloti (Xu et al. 2010; Tu et al. 2011).
Chlorpyrifos is one of the most widely used insecticides to control mosquitoes
(larvae and adults), flies, and various soil, leaf crop, and household pests. Klebsiella
38
A. Sehrawat et al.