Pseudomonas putida: An Environment Friendly Bacterium 133

contaminated soil (Kumar et al. 2012). After nitosoguanidine treatment, phenotypically favourable

strains were chosen for protoplast fusion (Dai et al. 2005, Singleton et al. 2009, Dai and Copley

2004, Gong et al. 2009). As a result, the SF-IOC11-16A strain created by genome shuffling was

efficient in degradation of PAHs (Kumar et al. 2012).

8.3.11 Naphthalene

Naphthalene degradation is associated with Pseudomonas putida PpG7 (Dunn and Gunsalus 1973),

P. paucimobilis Q1 (Kuhm et al. 1991) and P. putida ND69 (Song et al. 2018). In 48 hr, the latter

can degrade up to 98% of 2mg L^–1 naphthalene. Jia Yan et al. (2008) observed the degradation of

naphthalene in Pseudomonas N7 in 2008; the degradation rate reached 95.66%. The naphthalene

degrading gene in P. putida ND6 is found on pND 6-1, a 102 kb plasmid. pND 6-1 has a G + C content

of 57%, which includes the oriV, the region related to plasmid replication and stable inheritance, and

the naphthalene degradation gene region. For naphthalene degradation, there are 23 coding domains

(Li et al. 2004). The genes involved are nahG, which codes for salicylic acid hydroxylase, and nahR,

that codes for NahR, a transcriptional regulatory protein of the LysR family. The gene nahY encodes

a naphthalene chemotactic protein, while the gene nahV encodes a salicylaldehyde dehydrogenase

(Song et al. 2018).

8.3.12 Toluene

The strain P. putida DOT-T1E is rifampin resistant. It can withstand supersaturating toluene

concentrations (Ramos-Gonza’lez et al. 2003). Toluene is used as a carbon and energy source (Ramos

et al. 1995). The mechanism is the tod-pathway, which converts toluene into 3-methylcathecol, is

then used in the Krebs cycle (Mosqueda et al. 1999). P. mendocina KR1 metabolizes toluene to

p-cresol via the T4MO pathway using the tmo gene product (Whited and Gibson 1991). Pcu genes

further oxidize this to 4-hydroxybenzoate. 4-HBA is a precursor to paraben and methylparaben,

which are used in the production of liquid glass and antimicrobial agents (Huang et al. 1992, Soni

et al. 2002). Toluene is also converted into 4-HBA by P. putida DOT-T1E. To prevent toluene and

4-HBA from being misrouted, the tod and beta-ketoadipate pathways were turned off to maximize

product formation (Ramos-Gonza’lez et al. 2003).

8.4 Biosynthesis of Value-added Products

P. Putida is not only proven to demineralize the xenobiotic compounds like pesticides, but also

been explored to synthesize value-added products. These products are synthesized mostly using

waste material that may not be degraded by common bacteria. Some products are synthesized as

intrinsic property and others after introducing heterologous genes from various microorganisms.

Use of P. putida for synthesis of all the compounds discussed below by P. putida is one of the best

eco-friendly options.

8.4.1 Production of Ethylene

Ethylene is a vital petroleum-derived raw material in the chemical industry (Kniel et al. 1980).

However, as petroleum reserves deplete, alternatives should be found. Pseudomonas syringae and

Penicillium digitatum, for example, produce ethylene from 2-oxoglutarate. There are two methods

for producing ethylene. The first uses 2-oxo-4-methylthiobutriyric acid (KMBA) as a precursor,

while the second uses 2-ketoglurate (Chagué et al. 2002). The ethylene-forming enzyme (EFE) is

responsible for ethylene production. This gene was cloned from endogenous plasmids of P. syringae

pv. glycinea. Through double crossover recombination, efe gene was integrated into the P. putida

K2440 16S rDNA sites of P. putida KT2440 (Watanabe et al. 1998). It contains seven identical

copies of 16S rDNA, so efe gene can be integrated multiple times without causing any harm; and

the ethylene production can be increased even further. P. putida was given pMEFE1, a plasmid with