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Wastewater were collected from the effluent channel in the vicinity of Mathura oil refinery, U.P. (India) and analysed for physicochemical characteristics, heavy metals as well as organic compounds including PAHs. The interaction of PAHs and heavy metals with various group of microorganisms revealed the viable count of aerobic heterotrophs, asymbiotic nitrogen fixers, actinomycetes and fungi were found to be 2.38 Â 10 6 , 1.89 Â 10 4 , 2.20 Â 10 4 CFU/mL and 8.76 Â 10 3 CFU/mL respectively. We have selected and screened 50 bacterial isolates for their resistance/tolerance to heavy metal and PAHs. Out of 25 multi-metal resistant isolates, 6 were able to tolerate PAHs at the concentration of 5000 μg/mL (50μg/disc) to naphthalene, anthracene, phenanthrene and pyrene. The PAH degradation efficiency of the isolates was assessed using spectrophotometer with 100 μg/mL of phenanthrene and observed different degree of degradation ranging from 34-66% after 96 h of incubation. One of the bacterial isolates KWB3 (identified as Enterobacter ludwigii by 16S rDNA sequencing) exhibited maximum degradation efficiency (66%) was further tested for phenanthrene degrading ability in the presence and absence of a co-substrate (glucose) in a mineral salt medium; and a number of metabolites were produced and detected by GC-MS which revealed the presence of benzocoumarin, phthalic acid, catechol and several low molecular weight compounds. The DNA derived from multi-metal and PAHs tolerant bacteria were PCR amplified using Inc specific primers and positive PCR products were obtained with oriT and trfA2 of the IncP group; indicates that these bacteria have gene-mobilizing capacity.

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Petroleum refinery wastewater combined with domestic sewage were collected from the open channel in the vicinity of Mathura oil refinery, UP (India) and analysed by inductively coupled plasma optical emission spectrometry (ICP-OES) and gas chromatography-mass spectrometry (GC-MS) for elemental analysis and organic pollutants, respectively. Several potentially toxic and non-toxic elements were found to be present in the wastewater samples. GC-MS analysis revealed the presence of several organic contaminants including pesticides. Wastewater samples were extracted using amberlite XAD4/8 resins and liquid-liquid extraction procedures using different organic solvents. The extracts were tested for their cyto-genotoxic potential using bacterial (Salmonella mutagenicity test, E. coli K-12 DNA repair defective mutants, Bacteriophage λ assay) and plant (Vigna mungo phytotoxicity test, Allium cepa chromosomal aberration assay) systems. A significant increase was observed in the number of revertants of TA97a, TA98 and TA100 strains with the test samples and XAD concentrated samples were found to be more mutagenic than liquid-liquid extracts. Colony forming units (CFUs) of DNA repair defective mutants of E. coli K-12 recA, lexA and polA declined significantly as compared to their isogenic wild-type counterparts with the test samples. Significant reduction in plaque forming units (PFUs) of bacteriophage λ was also found on treatment with the solvent extracts. Presence of several toxic pollutants in the wastewater apply prohibitive action on the seed germination process. Germination rate of Vigna mungo seeds as well as radicle and plumule lengths were found to be affected when treated with different concentration of wastewater as compared to control. Present study also indicated concentration dependent reduction in mitotic index of A. cepa i.e., 16.38% at 5% and 9.74% at 100% wastewater and percentage of aberrant cells were highest at 100% effluent. Present findings indicated that mutagenicity/genotoxicity of wastewater is due to the mixture of genotoxins; poses serious hazards to the receiving waterbodies which require continuous monitoring and remedial measures for their improvement.

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Micronutrients are essential minerals required for the development of plants and humans, but they are often lacking in soils and food crops. Despite the fact that soils might contain substantial amount of micronutrients, their bioavailability in rhizosphere could be controlled by the combined effects of several edaphic factors, such as competing cations, anions, organic matter, pH, soil morphology, soil parent materials and biological factors, including plant characteristics as well as interaction of plant roots with microorganisms. Plant growth-promoting microbes belonging to cyanobacteria, bacteria, fungi and mycorrhizae can influence micronutrients availability by the process of solubilization, chelation and oxidation-reduction reactions in soil. Some microorganisms activate the release of root exudates by interacting with the plant roots. Moreover, their amount as well as composition affects the microbial diversity and activity of plant-associated beneficial microorganisms which ultimately affect the nutrient availability. Exuded carboxylates, that is, organic acids, may have role in solubilization of mineral nutrients as well as growth substrates for microbes. Some typical organic acids (such as lactate, citrate, acetate and oxalate) are found in the root exudate, which can convert the micronutrients in the plant-available forms to be transported across the plasma membrane of the root cells. Since soil microbial flora are not nutrient deficient in low-nutrient soil, they may be helpful towards increasing the soil micronutrient availability, plant uptake and also its accumulation in grains, that is, biofortification in a range of crops. This chapter describes the physiological importance of micronutrients in plants as well as improvements of nutrient uptake and utilization by plant systems.

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