Copper accumulation by Eichhornia crassipes and role of rhyzospheric bacteria

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

San Miguel de Tucumán

Congreso; VII Congreso Argentino de Microbiología General "SAMIGE del Bicentenario"; 2011

SAMIGE -Sociedad Argentina de Microbiología General

The elevated 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 ion. Rhizospheric microbes can increase the tolerance of their host plants against heavy metal stress. The aim of this research is to assess the copper removal efficiency and tolerance of water hyacinth harvested in Riachuelo and tolerance of its rhizospheric bacteria. Harvested water hyacinths were grown in Hoagland nutrient solution for 50 days outdoors. Three treatments with this solution and different added copper 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 °, and 11:13 photoperiod 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 later counting of mesophilic aerobic bacteria tolerant to copper. Morphologically different colonies were selected to study the tolerance to copper. The counts were performed by surface plating in Petri dishes, using minimal medium supplemented with 100 mg / L of copper. The level of tolerance to copper was studied by sowing in Petri dishes with minimal medium supplemented with 200 mg / L, 500 mg / L, 1000 mg / L and 2000 mg / L of copper. The plants absorbed copper mainly in the roots in proportion to the supply (Control: 0.082; T1: 13.5 and T2: 23.8 mg Cu g−1 dry weight). The translocation rate was low and copper concentrations in the belowground parts were: in Control: 0.016, T1: 0.056 and en T2: 0.133mg Cu g−1 dry weight. Productivity declines corresponding to the increase in the concentration of copper  (Control: 0.57 g/pot. day and T2: 0.25 g/pot. day). Also, total chlorophyll concentration was in T2: 0.004 mg/cm2 and 0.037 mg/cm2 in Control. The counts of mesophilic aerobic bacteria resistant to 100 mg / L of copper in the control ranged between 9.2 x 105 cfu / g and 1.4 x 106 cfu / g, at T1 ranged from 6.4 x 106 cfu / g and 1.1 x 107 cfu / g while T2 values ​​were between 6.6 x 106 and 1.6 x 107 cfu / g. The 81.8% of the selected bacteria tolerated 2000 mg / L of metal. 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 mesophilic aerobic bacteria resistant to 100 mgCu / L were higher than control and were highly tolerant to copper. However, rhizospheric microorganisms did not seem to improve the uptake and toxicity symptoms in plants.