Screening of multiple metal and antibiotic resistant isolates and their plant growth promoting activity.
Heavy metal contamination has accelerated due to the rapid industrialization world wide. Accumulation of metals in excess can modify the structure of essential protein or can replace an essential element. Bradyrhizobium strains showed tolerance to cadmium, chromium, nickel, lead, zinc and copper. All the isolates showed maximum tolerance towards lead and zinc which was followed by nickel and chromium. These strains also showed tolerance towards most of the antibiotics. Bradyrhizobium strains were also tested for their Plant Growth Promoting (PGP) substances, all isolates produced good amount of indole acetic acid and were positive for ammonia but only three strains were positive for HCN and siderophore (RM1, RM2 and RM8), the rest isolates showed negative result. Based on the above intrinsic abilities of Bradyrhizobium species, these strains can be used for the growth promotion, as well for the detoxification of the heavy metals in metal polluted soils.