Phytostimulation of atrazine degradation by alfalfa (Medicago sativa, L.) extracts and exudates

CUADRADO, V; MERINI, LJ; GIULIETTI, AM

Rimini

Congreso; 14th International Biotechnology Symposium and Exhibition; 2010

Agricultural soils receive intensive application of different pesticides, which usually cause contamination of soil and water. Atrazine is among the main herbicides applied for maize and other crops, in different parts of the world. Contamination with atrazine is well documented, as well as its toxicity (Fan et al., 2007; Graziano et al., 2006). For this kind of contamination, rhizoremediation appears as an emergent technology that makes use of both plant and microbes capacities for organics degradation (Kuiper et al., 2004). Two different bacterial consortia (6I7 and 7G1), isolated from agricultural soils of Argentinean Humid Pampa region (Cuadrado et al., 2008), demonstrated degradation activity while growing on atrazine as sole C and N source. Plant root and seed extracts and exudates were obtained from alfalfa, and characterized in their chemical composition. Glucose and galactose as monosacharides and different amino acids were detected, especially in seed exudates. However, their concentrations were only a low percentage in relation to the total organic carbon content. Both bacterial consortia were able to grow on seed exudates as sole nutritional source or as additional substrate in the presence of atrazine, showing an increase in biomass yields (7G1 40%; 6I7 58%) and no modification of the degradation rates. On the other hand, after a short-term exposure to root exudates, consortium 6I7 showed a significant increase in growth rate and faster atrazine degradation (5 days), in comparison with the consortium without any exposure to plant material (7 days for complete atrazine removal). This demonstrated the phytostimulation of atrazine degradation caused by compounds present in root exudates, acting as growth enhancers, enzymatic inductors or cometabolites for any member/s of the bacterial consortium. In addition, direct effect of vegetal exudates over atrazine degradation was tested. Seed exudates at 100:1 ratio with atrazine, produced a 27% reduction in herbicide concentration after 52 hs. Detection of hidroxy-atrazine in the medium confirmed the chemical activity ‘per se’ of some compounds present at seed exudates. In conclusion, this work provides proof about direct and indirect stimulation of alfalfa exudates over atrazine degradation