Effect of root exudates of maize plants on lindane removal by Streptomyces strains

YAÑEZ, LM; A ALVAREZ; BENIMELI C.S.; AMOROSO M.J.

Puerto Vallarta

Simposio; 16th International Symposium on the Biology of Actinomycetes; 2011

Lindane [γ-hexachlorocyclohexane (γ-HCH)] is a cyclic chlorinated insecticide, which has been used worldwide for crop protection. Because of its high toxicity it has caused serious environmental problems so, it is imperative to develop methods to remove γ-HCH. One of the strategies adopted is bioremediation using Actinobacteria. On the other hand, root exudates are products released by plants with significant levels of carbon. These plant products not only promote growth of microbial degraders in the rhizosphere but also have degrading-activities. In this context, the objective of this study was to evaluate the effect of root exudates (RE) of maize on γ-HCH removal by indigenous Streptomyces strains. RE were collected from plants that growing in Hoagland solution. Lyophilized exudates were diluted in water, sterilized by filtration (0.22 µ) and stored. Streptomyces sp. M7, A5 and A11 were cultured in minimal medium (MM) supplemented with exudates and/or glucose (1 g L-1) and spiked with γ-HCH (1.66 mg L-1). Cultures were incubated at 30ºC at 150 rpm for seven days. Similar experiments were carried out in MM without carbon sources as controls. Regarding composition, carbohydrate and total protein content of exudates were 0.88 ± 0.02 (g L-1) and 193.5 ± 16.0 (µg ml-1), respectively. All strains were able to growth on MM supplemented with exudates as sole carbon source (Table). The highest values of removed pesticide were registered when Streptomyces sp. A5 was cultured in presence of exudates and lindane (55.0 %) and when these were spiked with γ-HCH, without microorganism (42.6 %). It could be possible that root exudates of maize enhanced removal of γ-HCH by stimulation of γ-HCH-degrading activity either the actinobacteria or the plant product. In contrast, Streptomyces sp. A11 did not remove γ-HCH in presence of exudates suggesting that γ-HCH-degrading activity was repressed after incubation on this condition. Treatment Strain Growth [dry weight (g L-1 ± SE)] γ-HCH removed (% ± SE ) A5 M7 A11 A5 M7 A11 γ-HCH + exudates 1.02 ± 0.3 0.5 ± 0.09 0.7 ± 0.08 55.0 ± 7.7 35.7 ± 6.0 0 Exudates 0.8 ± 0.1 0.4 ± 0.06 0.6 ± 0.01    γ-HCH 0.5 ± 0.1 0.1 ± 0.02 0.8 ± 0.1 32.8 ± 1.4 45.3 ± 4.1 15.6 ± 0.4 γ-HCH + Glu 0.7 ± 0.1 0.3 ± 0.02 0.7 ± 0.04 8.5 ± 6.9 10.4 ± 0.7 23.1 ± 11.2 Glucose 0.7 ± 0.01 0.6 ± 0.03 0.8 ± 0.23    γ-HCH + exudates    42.6 ± 1.4 42.6 ± 1.4 42.6 ± 1.34