Characterization of lead-resistant and ACC deaminase-producing endophytic bacteria and their potential in promoting lead accumulation of rape

Forty-nine lead (Pb)-resistant endophytic bacteria were isolated from metal-tolerant Commelina communis plants grown on lead and zinc mine tailing, of which, seven 1-aminocyclopropane-1-carboxylate (ACC) deaminase-producing endophytic bacteria were initially obtained and characterized with respect to heavy metal resistance and production of ACC deaminase, indole-3-acetic acid (IAA) as well as siderophores. Two isolates (Q2BJ2 and Q2BG1) showing higher ACC deaminase activity were evaluated for promoting plant growth and Pb uptake of rape grown in quartz sand containing 0 and 100 mg kg−1 of Pb in pot experiments. The seven Pb-resistant and ACC deaminase-producing endophytic bacterial isolates were found to exhibit different multiple heavy metal resistance characteristics and to show different levels of ACC deaminase activity (ranging from 12.8 μM α-KB mg−1 h−1 to 121 μM α-KB mg−1 h−1). Among the seven isolates, six isolates produced indole acetic acid, whilst five isolates produced siderophores. In experiments involving rape plants grown in quartz sand containing 100 mg kg−1 of Pb, inoculation with the isolates resulted in the increased dry weights of above-ground tissues (ranging from 39% to 71%) and roots (ranging from 35% to 123%) compared to the uninoculated control. Increases in above-ground tissue Pb contents of rape cultivated in 100 mg kg−1 of Pb-contaminated substrates varied from 58% to 62% in inoculated-rape plants compared to the uninoculated control.