Effects of Fe-oxidizing bacteria (FeOB) on iron plaque formation, As concentrations and speciation in rice (Oryza sativa L.)

Large areas of the paddy fields in South China are contaminated with arsenic (As), which causes serious problems, including high As concentrations in brown rice. Three As-resistant iron-oxidizing bacteria (FeOB) namely, Bacillus sp. T2, Pseudomonas sp. Tangling 14 and Bacillus sp. TF1-3, were isolated and applied to rice grown in different As-contaminated environments to study the effects of FeOB on the As accumulation in rice and clarify the possible mechanisms involved. The results showed that FeOB inoculation significantly decreased the inorganic As concentrations in brown rice grown in pots and paddy fields by 3.7-13.3% and 4.6-12.1%, respectively. FeOB inoculation enhanced the formation of Fe plaque, which sequestered more As on the root surface. Moreover, a significantly lower level of As(III) influx was observed in the rice cultivated with FeOB than in the control. FeOB inoculation also decreased the As concentrations in pore water and the Fe(II)/Fe(III) ratio in rhizosphere soil. The present results suggest that FeOB inoculation decreased the inorganic As concentrations in brown rice by affecting the formation of Fe plaque, As(III) uptake kinetics and rhizosphere soil properties. Based on our results, FeOB inoculation could be considered a useful method to decrease inorganic As concentrations in brown rice grown in As-contaminated paddy fields.