Assessment of microbial communities in mung bean (Vigna radiata) rhizosphere upon exposure to phytotoxic levels of Copper

Pollution of agricultural soils by Cu is of concern as it could bring about alterations in microbial communities, ultimately eliminating certain plant beneficial bacteria thus disturbing soil fertility and plant growth. To understand the response of rhizobacterial communities upon Cu perturbation, mung bean (Vigna radiata) plants were grown in agricultural soil amended with CuSO4 (0-1000mgkg(-1)) under laboratory conditions. Culture-independent and -dependent Denaturing Gradient Gel Electrophoresis (CI-DGGE and CD-DGGE) fingerprinting techniques were employed to monitor rhizobacterial community shifts upon Cu amendment. In group specific PCR-DGGE, a negative impact was seen on -Proteobacteria followed by -Proteobacteria resulting in a concomitant decrease in diversity indices with increased Cu concentration. No significant changes were observed in Firmicutes and Actinomycetes populations. In CD-DGGE rhizobacterial community shift was observed above 500mgkg(-1) (CuSO4), however certain bands were predominantly present in all treatments. Plants showed toxic effects by reduction in growth and elevated Cu accumulation, with root system being affected prominently. From this study it is evident that above 250mgkg(-1), rhizobacterial communities are adversely affected. -Proteobacteria was found to be a sensitive bio-indicator for Cu toxicity and is of particular significance since this group includes majority of plant growth promoting rhizobacteria.