Effect of citric acid and rhizosphere bacteria on metal plaque formation and metal accumulation in reeds in synthetic acid mine drainage solution

• Assessed interactions among citric acid, rhizosphere bacteria and metal uptake in reed.
• Iron oxidizing bacteria (Fe(II)OB) enhanced the formation of Fe plaque.
• Fe plaque did not inhibit Fe, Al and Mn uptake in reeds.
• Citric acid inhibited Fe(II)OB growth and decreased metal plaque formation.
• Citric acid increased the metal accumulation in reeds.

Many of regions in the world have been affected by acid mine drainage (AMD). The study assessed the effect of rhizosphere bacteria and citric acid (CA) on the metal plaque formation and heavy metal uptake in Phragmites australis cultured in synthetic AMD solution. Mn and Al plaque were not formed, but Fe plaque which was mediated by rhizosphere iron oxidizing bacteria (Fe(II)OB) was observed on the root system of reeds. Fe plaque did not significantly influence the uptake of Fe, Al and Mn into tissues of reeds. CA significantly (p<0.01) inhibited the growth of Fe(II)OB and decreased the formation of Fe plaque. CA also significantly improved (p<0.05) the accumulation of Fe, Mn and Al in all the tissues of reeds. Roots and rhizomes were the main organs to store metals. The roots contained 0.08±0.01 mg/g Mn, 2.39±0.26 mg/g Fe and 0.19±0.02 mg/g Al, while the shoots accumulated 0.04±0.00 mg/g Mn, 0.20±0.01 mg/g Fe, 0.11±0.00 mg/g Al in reeds cultured in solution amended with 2.101 g/l CA and without inoculation of rhizosphere bacteria.