Influence of cadmium resistant bacteria on promoting plant root elongation and increasing cadmium mobilization in contaminated soil

Abstract

Plant roots and rhizosphere soils collected from cadmium-contaminated areas were screened for bacteria capable of offering resistance to cadmium. Three isolates designated as CR 191, CR20I, and TM6 were found to be highly resistant to cadmium toxicity. Among these, CR 191 and CR20I produced indole-3-acetic acid (IAA) in a 48 hr growth period of 57.20 ± 1.35 and 48.77 ± 1.10 mg/1, respectively; however, TM6 produced a low level of IAA of 14.10 ± 0.97 mg/1. Further, CR 191 and CR20I were identified by 16S rDNA sequence analysis as Enterobacter sp. and TM6 belonged to the genus Arthrobacter sp.. It was also observed that Enterobacter sp. CR 191 and Enterobacter sp. CR20I as IAA-producing bacteria stimulated root elongation of Ocimum gratissimum under cadmium toxic condition. The ability of these cadmium resistant bacteria to increase cadmium mobilization in contaminated soil was studied and it was found that only Arthrobacter sp. TM6 was able to increase cadmium mobilization in soil. The potential of Arthrobacter sp. TM6 to increase soil cadmium mobilization might be related to the production of exopolysaccharide (EPS). In addition, Arthrobacter sp. TM6 produced EPS maximally at the stationary phase (24 hr) of 5.51 ± 0.15 mg/l. These findings suggest that the co-bioaugmentation of IAA-producing cadmium resistant bacteria and Arthrobacter sp. TM6 could be useful in the further development of microbes-assisted phytoextraction techniques for the reclamation of cadmium-contaminated areas. © by PSP.