**8. Biodegradation of PAH**

Many bacterial, fungal and algal strains have been shown to degrade a wide variety of PAHs [88]. The most commonly reported bacterial species include *Acinetobacter calcoaceticus, Alcali‐ gens denitrificans, Mycobacterium* sp., *Pseudomonas putida, Pseudomonas fluorescens, Pseudomonas vesicularis, Pseudomonas cepacia, Rhodococcus* sp., *Corynebacterium renale, Moraxella* sp., *Bacillus cereus, Beijerinckia* sp., *Micrococcus* sp., *Pseudomonas paucimobilis* and *Sphingomonas* sp*.* [89]. *Pseudomonas putida* is a good candidate for metabolic engineering and genetic manipulation applications for expression of genes encoding several degradative enzymes [88]. Therefore, a *P. putida* strain was engineered to increase the efficiency of degradation of naphthalene and salicylate [88]. Similarly, another study demonstrated the efficiency of the naphthalene degradation process performed by different microbial strains of the genera *Pseudomonas* and *Burkholderia* in soil model systems [90]. Previous, studies have shown that bacteria can degrade BaP when grown on an alternative carbon source in liquid culture experiments [91]. Sor‐ khoh*et al.* [93] isolated spore forming PAHs degrading bacteria and reported their subsequent genetic studies of their degradation pathways which may lead to the discovery of novel genes involved. Various studies showed the significance of the rhizospheric effect on degradation of organic pollutant molecules [94].

In recent past, Bisht *et al*. [44] reported four bacteria from non-contaminated rhizospere of *P. deltoides* which were able to degrade 80-90% degradation of anthracene and naphthalene within 6 days. The maximum degradation pathways were reported from *Mycobacterium vanbaalenii* because of its exceptional ability to degrade a great variety of low and high molecular weight PAHs oxidatively in soil versatility of this species makes it probable inoculants in the remediation of PAHs contaminated sites [95].

*Calotropis* sp. as a dominant and common desert plants that grows widely in warm and urbanizing regions and has a high capacity for taking heavy metals into its tissues due to their abilities to absorb and tolerate heavy metals [96]. The use of the leaf biomass of *Calotropis procera* can be employed as good bio-sorbent for the removal of Cr (III) from aqueous solutions and as an alternative method of their removal from industrial effluent [97].
