Copper accumulation by Eichhornia crassipes and role of rhyzospheric bacteria

MELIGNANI, E.; DE CABO, L.; FORTUNATO, MS; GALLEGO, A.; KOROL, S.

Tucumán

Congreso; VII Congreso Argentino de Microbiología General; 2011

Asociación Argentina de Microbiología

The high levels of heavy metals in lower basin of Matanza-Riachuelo river would affect soil and water quality which consequently hampers plant growth. The recent management government plan includes revegetation with native plants. Water hyacinth (Eichhornia crassipes (Mart.)) grows in heavily polluted water bodies like Matanza-Riachuelo river and accumulates metal ions. Rhizospheric microbes can increase the tolerance of their host plants against heavy metal stress. The aims of this research are a) to assess the removal efficiency and copper tolerance of E. crassipes harvested in Riachuelo b) to evaluate copper tolerance of its rhizospheric bacteria. Harvested water hyacinths were grown outdoors in Hoagland nutrient solution for 50 days. Three treatments with this solution and different added copper concentration were performed: Control (0.1mg Cu l-1), T1 (15 mg Cu l-1) and T2 (25 mg Cu l-1). Water hyacinths of uniform size, previously rinsed with de-ionized water were placed in plastic containers of 2.8 cm2, were grown in a greenhouse, at room temperature between 19-23 °C, 11:13 photoperiod and pH: 4.12-5.14. Harvested at 7 days, total chlorophyll was determined in leaves. Final dry weight was determined in above and belowground parts and copper concentrations in water and plant tissues. Roots were separated in sterile vials for bacterial count. Bacterial count was performed by spreading on the surface of minimal medium supplemented with 100 mg l-1 of copper. Morphologically different colonies were selected to study the copper tolerance. The level of tolerance was evaluated by streaking on the surface of minimal medium supplemented with 200 mg l-1, 500 mg l-1, 1000 mg l-1 and 2000 mg l-1 of copper. Plants absorbed copper mainly in the roots according to supply (Control: 0.082; T1: 13.5 and T2: 23.8 mg Cu g−1 dry weight). Translocation rate was low and copper concentrations in the belowground parts were: Control: 0.016, T1: 0.056 and T2: 0.133 mg Cu g−1 dry weight. Productivity declines corresponding to the increase in copper concentration (Control: 0.57 g/pot. day and T2: 0.25 g/pot. day). Total chlorophyll concentration was: Control: 0.037 mg/cm2 and T2: 0.004 mg/cm2. The number of bacteria cell resistant to 100 mg l-1 of copper ranged between 9.2 x 105 - 1.4 x 106 CFU g-1 in the control and 6.4 x 106 - 1.1 x 107 CFU g-1 in T1, while T2 values were between 6.6 x 106 and 1.6 x 107 CFU g.-1 The 81.8% of the selected bacteria tolerated up to 2000 mg l-1 of copper. E. crassipes was capable of removing copper during incubation period with some symptoms of toxicity (chlorophyll and productivity decreasing). In T1 and T2, the numbers of bacteria resistant to 100 mg l-1 Cu were higher than control and were highly tolerant to copper. However, rhizospheric microorganisms did not seem to improve the uptake and plant toxicity symptoms.