40
(from Pseudomonas sp. strain NRRL B-12227) with only nine amino acid substitutions in response to atrazine induction. Despite of 98% sequence similarity, they are
functionally different. AtzA is a dechlorinase with no deaminase activity, while
TriA is a deaminase with low dechlorinase activity. TrzN is a zinc-dependent amidohydrolase which is ∼25% identical to atzA (Mulbry et al. 2002). TrzN is a dimer
containing a single Zn
2+
bound in each active site. Both AtzB and AtzC
(N-isopropylammelide aminohydrolase) have a zinc metal centre in the active site.
Shapir et al. (2002) reported that molecular weight of AtzC holoenzyme is 174,000
and has a subunit size of 44,938 kDa. The activity of metal-depleted AtzC can be
restored with Zn(II), Fe(II), Co(II), Mn(II), and Ni(II) salts. AtzD enzyme is a member of a family of ring-opening amidases. Apart from those enzymes discussed earlier, some other enzymes are reported to involve in the mineralisation of atrazine in
few organisms. These include Rhodococcus sp. N186/21 cytochrome P450 (Nagy
et al. 1995). Smith et al. (2005) reported that Nocardia converted hydroxyatrazine
to N-ethylammelide via an unidentified gene product.
S-Triazine-Degrading Genes
Triazine-degrading genes may be located on large plasmids or on the bacterial chromosome (Devers et al. 2007). The atzABCDEF gene composition was found only
in few bacterial strains including Pseudomonas sp. ADP and Agrobacterium sp.
NEA-D and is located on a unique plasmid of 110 kb for ADP (pADP1 plasmid)
and 137 kb for NEA-D. Atrazine mineralisation was well studied using Pseudomonas
sp. ADP. AtzABC genes are dispersed in an unstable region and flanked by insertion
elements with high homology to the known transposable DNA elements, IS1071
and IS801. The rearrangements result in the stochastic loss of one, two, or all three
atz genes. In the absence of atrazine selection pressure, atzB can be easily lost as in
Aminobacter ciceronei strain C147 formerly Pseudaminobacter sp. (Topp et al.
2000). The genes encoding atzDEF are clustered in the atzDEF operon, which is
located in a stable region of pADP-1. Adaptation of soil microflora to atrazine degradation or mineralization may rely on horizontal gene transfer and repeated exposure. Atrazine mineralization greatly depends on regulatory phenomena in response
to nitrogen limitation and transcriptional activation by LysR-transcriptional regulators. Devers et al. (2007) reported the presence of TrzN gene in Gram-negative
bacteria such as Sinorhizobium sp. and Polaromonas sp.
Recombinants and Formulations
Genetically engineered microorganisms overexpressing catabolic genes considerably
amplify the degradation in heavily atrazine-contaminated soils. Strong et al. (2000)
employed transgenic AtzA-expressing E. coli to remove residual atrazine contamination in situ of soil contaminated with 29 g L
−1
atrazine. Benson et al. (2018) observed
superior biodegradation of atrazine by recombinant E. coli- expressing atrazine
K. Rajendran et al.
(from Pseudomonas sp. strain NRRL B-12227) with only nine amino acid substitutions in response to atrazine induction. Despite of 98% sequence similarity, they are
functionally different. AtzA is a dechlorinase with no deaminase activity, while
TriA is a deaminase with low dechlorinase activity. TrzN is a zinc-dependent amidohydrolase which is ∼25% identical to atzA (Mulbry et al. 2002). TrzN is a dimer
containing a single Zn
2+
bound in each active site. Both AtzB and AtzC
(N-isopropylammelide aminohydrolase) have a zinc metal centre in the active site.
Shapir et al. (2002) reported that molecular weight of AtzC holoenzyme is 174,000
and has a subunit size of 44,938 kDa. The activity of metal-depleted AtzC can be
restored with Zn(II), Fe(II), Co(II), Mn(II), and Ni(II) salts. AtzD enzyme is a member of a family of ring-opening amidases. Apart from those enzymes discussed earlier, some other enzymes are reported to involve in the mineralisation of atrazine in
few organisms. These include Rhodococcus sp. N186/21 cytochrome P450 (Nagy
et al. 1995). Smith et al. (2005) reported that Nocardia converted hydroxyatrazine
to N-ethylammelide via an unidentified gene product.
S-Triazine-Degrading Genes
Triazine-degrading genes may be located on large plasmids or on the bacterial chromosome (Devers et al. 2007). The atzABCDEF gene composition was found only
in few bacterial strains including Pseudomonas sp. ADP and Agrobacterium sp.
NEA-D and is located on a unique plasmid of 110 kb for ADP (pADP1 plasmid)
and 137 kb for NEA-D. Atrazine mineralisation was well studied using Pseudomonas
sp. ADP. AtzABC genes are dispersed in an unstable region and flanked by insertion
elements with high homology to the known transposable DNA elements, IS1071
and IS801. The rearrangements result in the stochastic loss of one, two, or all three
atz genes. In the absence of atrazine selection pressure, atzB can be easily lost as in
Aminobacter ciceronei strain C147 formerly Pseudaminobacter sp. (Topp et al.
2000). The genes encoding atzDEF are clustered in the atzDEF operon, which is
located in a stable region of pADP-1. Adaptation of soil microflora to atrazine degradation or mineralization may rely on horizontal gene transfer and repeated exposure. Atrazine mineralization greatly depends on regulatory phenomena in response
to nitrogen limitation and transcriptional activation by LysR-transcriptional regulators. Devers et al. (2007) reported the presence of TrzN gene in Gram-negative
bacteria such as Sinorhizobium sp. and Polaromonas sp.
Recombinants and Formulations
Genetically engineered microorganisms overexpressing catabolic genes considerably
amplify the degradation in heavily atrazine-contaminated soils. Strong et al. (2000)
employed transgenic AtzA-expressing E. coli to remove residual atrazine contamination in situ of soil contaminated with 29 g L
−1
atrazine. Benson et al. (2018) observed
superior biodegradation of atrazine by recombinant E. coli- expressing atrazine
K. Rajendran et al.