Pseudomonas putida: An Environment Friendly Bacterium 131

(PNP) and dimethyl phosphorothioate but are unable to degrade PNP further. These bacteria were

used to clone ophc2, an organophosphorus hydrolase encoding gene. Cd can be immobilized

by bacteria such as P. aeruginosa KUCd1 and Pseudomonas sp. strain RB (Zhang et al. 2016).

A soil-dwelling bacterium was isolated having the potential of methyl parathion degradation ability.

The bacteria were responsible for producing the enzyme organophosphorus acid anhydrase, which

was responsible for the hydrolysis of methyl parathion into p-nitrophenol. Hydroquinone and 1, 2,

4-benzenetriol were produced eventually as a by-product of further degradation of p-nitrophenol.

At the end Maleyl acetate was produced by cleaving the last ring component, 1, 2, 4-benzenetriol,

which was catalyzed by the enzyme benzenetriol oxygenase (Rani and Lalithakumari 1994).

Pseudomonas sp., isolated from a mixed population of methyl parathion and parathion-degrading

bacteria, can hydrolyze the MP to p-nitrophenol and demands glucose and other carbon sources

for growth (Chaudhry et al. 1988). Flavobacterium sp. isolate from the same mixed population

could convert pnitrophenol to nitrite. It can take up to 48 hr for both bacteria to mineralize methyl

parathion as their only carbon source. Surface expression of metal-binding proteins in host strains is

an effective way to increase heavy metal immobilization. To maximize bioremediation, an EGFP-

expressing X3 bacterium was metabolically engineered to have MP degrading genes as well as a

Cd-immobilization phenotype (Zhang et al. 2016).

8.3.5 1,2,3-trichloropropane (TCP)

TCP is a solvent, a precursor of soil fumigants, a catalyst in the synthesis of dichloropropene or

polyphsulfone liquid polymers (WHO 2003), and a toxic industrial waste classified as a persistent

pollutant (Dvorak et al. 2014). P. putida K2440 was designed to degrade 1,2,3-trichloropropane

(Gong et al. 2017). The microbe was engineered with haloalkane dehalogenase (Kulakova et al.

1997), haloalcohol dehalogenase (van Hylckama et al. 2001) from Rhodococcus rhodochrous

NCIMB 13064 and epoxide hydrolase (Rink et al. 1997) from Agrobacterium radiobacter AD1.

This engineered strain was capable of successfully converting up to 10 mg L^–1 of TCP (Dvorak

et al. 2014). The strain was further improved by deleting the glpR gene, which increased carbon

flux in this pathway, and improved the degradation with expression of Vitreoscilla haemoglobin,

in aerobic conditions. By deleting flagella-related genes, the energy charge and reducing power

were improved (Stark et al. 2015, Kim et al. 2005). The most common biological detoxification

mechanism is oxidative dehalogenation of pollutants, which is limited to oxic environments. As

a result, organohalide degradation is difficult in anoxic conditions (Janssen et al. 2001). P. putida

was engineered to contain several genes that participate in respiration by facultative anaerobes and

aerotolerant bacteria. These genes include the haloalkane dehalogenase activity from Pseudomonas

pavonaceae 170, the acetate kinase (ackA) gene of the facultative anaerobe Escherichia coli, and

the pyruvate decarboxylase (pdc) and alcohol dehydrogenase II (adhB) of Zymomonas mobilis.

Under anoxic circumstances, the recombinant strain proved successful in degrading pollutants such

as 1,3-DCP (Nikel and de Lorenzo 2013). Another method involved the expression of Vitrescilla

haemoglobin (VHb) in P. putida KTUe. This made it possible for the microbe to proliferate more

quickly in environments with a scarcity of oxygen. The capacity of the strain to bind oxygen is

improved by the presence of VHb.

8.3.6 Phenol

Phenol is widely used and is a unfavourably industrial waste produced by petroleum refineries

(NPCS Board of Consultants and Engineers 2000). As it quickly penetrates to the skin and can cause

irritation to the eyes, respiratory tract and can be fatal in chronic exposure. The use is unavoidable

leaving an option of maintaining the permissive limit. The maximum allowed level is 2ppm and

can be maintained below or neutralized to zero level using P. putida. P. putida FNCC-0071 cells

immobilized in alginate beads were used to degrade phenol (Hannaford and Kuek 1999). About

600 ppm of phenol was degraded within 48 hr without affecting viability. Recently, a constant