No abstract

Macro and micronutrients are vital for the growth and productivity of the plants. Zinc (Zn) is considered to be one of the essential micronutrients for the growth and development of cereals as well as fodder crops. It is also a regulatory cofactor for all those enzymes which are required for the synthesis of chlorophyll, proteins and carbohydrates. The functioning of these enzymes is affected significantly due to Zn deficiency and there will be a retarded growth and productivity of plants. Deficiency of Zn is a universal problem among cereal crops. The concentration of Zn varies from 6-1.2 mg/kg in various soils, whereas its concentration reaches 20-300 ppm in plants. Zn deficiency leads to chlorosis in the leaves of plants. Various reasons affect the availability of Zn in the plants, which include soil type, pH of the soil and availability of other nutrients that work antagonistically for the absorption of Zn. Zn applied as the fertilizer gets converted into unavailable form by making insoluble complexes and thus not available for plants. Hence the best alternative to this issue is the use of Zn solubilising bacteria (ZSB). These ZSB will accumulate in the rhizosphere zone of the plants and will reduce the requirement of the applied Zn fertilizer. It will prevent Zn toxicity in the soil and will enhance the uptake of other macronutrients like phosphorus to the plants.

A transconjugant of Azotobacter chroococcum Mac 27 tagged with lac Z(A. chroococcum Mac27 L) was found to possess high levels of β-galactosidase activity constitutively. Further, the lac Z marker was found to be stably integrated into the chromosome of the A. chroococcum Mac 27 and did not have any adverse effect on growth, nitrogen fixation and excretion of ammonia. A quick method to determine the viable cell number in broth culture and carrier based inoculants has been developed on the basis of β-galactosidase assay. It was found that there was a direct relationship between the number of cell as determined by standard plate count and intensity of colour that developed upon degradation of ONPG due to β-galactosidase activity. The method was found to be sensitive enough to determine 1.7 × 106 CFU mL−1 in broth culture as well as carrier based Azotobacter inoculants. Further, it was observed that when A. chroococcum Mac27 L was inoculated on Brassica campestris, it could be detected in the presence of other bacteria capable of growing on Burks agar medium containing X-gal on the basis of lac Z genetic marker.

Wheat (Triticum aestivum) is a major cereal crop grown worldwide. Most of the world population depends on wheat for their nutrient requirement. Zinc (Zn) is one of the most crucial elements required for the development of wheat plant. It is one of the micronutrients required in many biochemical cycles. It has been found that the concentration of Zn is below the required level in the soil and hence it remains deficient in the crops. To ameliorate the deficit, chemical fertilizers are added in the soil, where as biofertilizers are preferred over chemicals in sustainable agriculture. The paper describes the isolation, screening and molecular characterization of the zinc solubilizing bacteria (ZSB) to improve plant growth. A total of 100 soil samples were collected from the rhizospheric soil of wheat plants. ZSB were isolated by dilution plating on Bunt and Rovira media. The 50 isolates were selected and screened for their Zn solubilization. The zinc tolerance of all the isolates varied from 0.5% to 2% of insoluble Zn. Based on the Zn tolerance ability, 15 bacterial isolates were screened for Phosphate solubilization and further analyzed for the synthesis of IAA, NH3, siderophore production and chitinase activity. The three isolates were selected on the basis of the plant growth promoting characteristics for molecular characterization and were found to be homologous to Bacillus cereus, Pseudomonas aeruginosa and Bacillus tropicus. This study documented the establishment and survival of ZSB in the wheat rhizosphere and enhanced plant productivity, thus indicating the potential of isolates as commercial biofertilizers.

Heavy metal contamination due to natural and anthropogenic sources is a global environmental threat which can produce harmful effects on human health when they are taken up in amounts that cannot be processed by the organism. Technologies involving microbial cells for metal removal and recovery may provide an alternative to conventional methods. In the present study, three cadmium resistant bacteria were isolated from soil collected from industrial area of Faridabad, Haryana, India. Screening of the bacterial isolates for metal resistance against Cd2+, Ni2+, Hg2+, Cu+2 and Pb2+ was done by determining the minimal inhibitory concentration ranging from 10ppm to 250ppm. Moreover these isolates showed a significant ability to remove 70 to 78% of cadmium. These isolates were identified as Bacillus sp.263ZY1 (MA5), Bacterium YC-LK-LKJ45 (MB5) and Bacillus subtilis strain DHXJ07(MC5) on the basis of 16S r-RNA gene sequencing. The ability of these microbes to tolerate high concentration of a range of heavy metals provides a scope of use of these bacterial strains for bioremediation of heavy metal from industrial effluent.