Rhizoremediation prospects of Polyaromatic hydrocarbon degrading rhizobacteria, that facilitate glutathione and glutathione-S-transferase mediated stress response, and enhance growth of rice plants in pyrene contaminated soil.

Rhizoremediation is a strategy where pollutant degrading bacteria are augmented through plant roots using plant-microbe interaction. Therefore, for effective rhizoremediation of pyrene contaminated soil, bacterial strains were experimented for amelioration of stress response in host plant along with biodegradation ability. A total of 28 bacteria, having ability to degrade polycyclic aromatic hydrocarbons were isolated from contaminated sites and checked for their plant growth promoting attributes, such as indole acetic acid (IAA) production, phosphate solubilization, atmospheric nitrogen fixation and siderophore release. Among these isolates, Klebsiella pneumoniae AWD5 was found to degrade 60% of pyrene. While other isolates, i.e. Alcaligenes faecalis BDB4, Pseudomonas fragi DBC, Pseudomonas aeruginosa PDB1, Acinetobactor sp. PDB4 degraded 48.5%, 50.29%, 31.3% and 36% of pyrene, respectively, after 6 days of incubation. K. pneumoniae AWD5 produced 94.2 μg/ml IAA and 3.1 mM/mg/h unit of ACC deaminase, which was best among eighteen indole acetic acid producers and five of the 1-aminocyclopropane-1-carboxylate (ACC) deaminase producing isolates. P. aeruginosa PDB1 resulted in highest phosphate solubilization activity of 875.26 ng/ml of soluble phosphate among seven phosphate solubilizers. The isolates AWD5 and PDB1 both have shown a good amount of siderophore release (56.3% and 84.3% unit). There was 19.1% increase in shoot length of rice seedlings treated with PDB1 in presence of pyrene. Similarly, 26.5% increase in the root length of AWD5 treated rice was recorded in pyrene contaminated soil. Bacterial inoculation also induced and improved the stress response in host plant, in presence of pyrene, as suggested by the superoxide dismutase, glutathione and glutathione-S-transferase activities in rice.