Screening And Growth Characteristics Of Strains Resistant To Heavy Metal Stress

Sustainable and environmentally friendly technologies are needed to provide more food for the world’s population,which is expanding quickly.A different approach to preventing soil contamination and maintaining agriculture for a sustainable economy is to employ Plant Growth Promoting Bacteria as a multifunctional biofertilizer or bio stimulant.Plant productivity can be increased by enhancing soil nutrient status with natural resources like PGPR.In present study,beneficial rhizobacteria were isolated from wheat(Pisum sativum)rhizosphere samples taken from three different places of district Dir lower Pakistan.30 isolates out of 60 were screened for plant growth promoting traits,antibacterial potential,ability to tolerate abiotic stress condition and check the growth rate of these isolates at wide range of p H and temperature.The main study results are presented as follows:(1)It was found that all Plant growth promoting rhizobacteria(PGPR)were recognized as promising phosphate solubilizers,B9,S5 and B4 showed best Phosphate solubilizing bacteria(PSB)activity.12 out of 30 bacterial isolates were able to fix atmospheric nitrogen,among them B9,W3 and B4 showed best result.All bacterial isolates were able for IAA production,the best result showed by S9 and B4.All bacterial isolates,with the exception of W2 and W6,produced catalase.4 isolates had negative results for oxidase activity,while 8 showed positive results.5 bacterial strains were positive and 7 strains tested negative for urease.(2)Among 30 strains,7 strains inhibited the growth of Ralstona solanacerum and 5strains were resistant to Xanthomonas citri.W1(32 mm)showed the greatest zone of inhibition against Ralstonia solanacearum.Similarly,B2(20.16 mm)showed the maximum inhibition zone against Xanthomonas citri.Lead(2.03)has the highest growth rate(OD)for heavy metal tolerance,followed by nickel(1.65)and cadmium(1.39).After4 h of incubation,p H 6(0.22),then p H8(0.21),showed the highest growth rate.In a similar way,after 24 h of incubation,p H7(1.42)showed the highest growth rate,followed by p H6(1.39).(3)Additionally,the growth of these bacterial isolates at various temperatures was examined.After 4 h of incubation,the growth rate reached its peak at 50℃(0.32)and was thereafter recorded at 20℃(0.30).In a similar manner,after 24 h of incubation,the highest growth rates were seen at 30℃(1.36),followed by 50℃(1.35).(4)Overall results revealed that the tested PGPR showed resistance to toxic heavy metals,Ralstonia solanacearum and Xanthomonas citri,and was able to grow in a variety of p H and temperature conditions.