Actinobacteria and maize plants: a promising biological system to remove lindane from soils

ALVAREZ, ANALÍA; POLTI, MARTA ALEJANDRA; BENIMELI, CLAUDIA SUSANA; CUOZZO, SERGIO ANTONIO; FUENTES, MARÍA SOLEDAD; SÁEZ, JULIANA MARÍA; COLIN, VERÓNICA LETICIA; DÁVILA COSTA, JOSÉ SEBASTIÁN; AMOROSO, MARIA JULIA

La Falda, Córdoba

Workshop; II Workshop Latinoamericano sobre PGPR; 2014

Universidad Nacional de Río Cuarto, Universidad Nacional de Quilmes, Universidad de Antioquia

Introduction. Highly toxic organochlorine pesticides (OPs) like lindane have been released into the environment. Although nowadays its use is banned, it continues causing serious environmental and health concerns. Actinobacteria have a great potential for the bioremediation of toxic compounds, while several plants not only promote growth of microbial degraders, but also have pesticide degrading-activities. Objective. To evaluate lindane dissipation by an actinobacteria consortium cultivated with maize plants. Materials and Methods. Four Streptomyces strains previously isolated from soils contaminated with OPs were cultured on pots filled with sterile soil spiked with lindane (2 mg Kg-1). Strains were inoculated in the pots as mixed culture and one maize plant was planted per pot. Treatments (repeated 3 times) were as follows: lindane-plant-consortium; plant-consortium; lindane-consortium and lindane-plant. Appropriates controls were made. Pots were incubated at 30 ºC, and soil samples were taken at 0,7,14 and 21 days for determining microbial growth (CFU g-1), residual lindane (by Gas Chromatography) and for ecotoxicity testing using lettuce seedlings. The vigor index (VI) of lettuce were calculated (VI=average seedlings length x percentage of germination/10). Results. The consortium was able to growth on the three conditions assayed, although differences among CFU g-1 per treatment and per time were registered. At the 7th day, the consortium grew more on the lindane-plant-consortium condition (1.0x106±1.5x105) than in the lindane-consortium condition (2.9x105±2.0x104) (P<0.05). Microbial growth in the plant-consortium condition was intermediate (5.9x105±5.3x104) to the growth registered on polluted soils (P>0.05). On the other hand, at 14 days, microbial growth was quite similar among the treatments (P>0.05). At 21 days, microbial growth reached almost the same value in lindane-plant-consortium (2.0x107±1.8x106) than in lindane-consortium condition (1.9x107±1.2x105). Microbial growth in the consortium-plant condition was slightly lower (1.0x107±4.5x105) than the growth registered on polluted soils (P>0.05). Significant microbial growth was not recorded in the controls. Pesticide dissipation was evidenced in all treatments, although this process was variable among them, along the time. From the 7th day, significant lindane dissipation was registered in lindane-plant-consortium as well as in the lindane-plant condition, reaching at the 14th day, 17.6±2.9% (lindane-plant-consortium) and 39.6±1.3% (lindane-plant) of  lindane removal (P<0.05). At the end of the experiment, highest value ​​of pesticide removal (61.6±1.7%) was obtained in lindane-plant-consortium condition while lindane removal in the lindane-plant condition was 54.5±1.3% (P>0.05). On the other hand,  the bioremediation process in the lindane-consortium treatment (without plant) was evidenced from the beginning of the experiment, reaching 13.7±1.2% of pesticide removal at the 7th day, 34.5±5.7% at 14 days and 37.8±5.6% at 21 days. Lindane removal obtained in this treatment at the end of the experiment, was different at statistical level (P<0.05) to the pesticide dissipation registered at the same time, in planted soils. Significant lindane removal was not recorded in the control soil. The effectiveness of the bioremediation process was evaluated by phytotoxicity test. In most cases, the VI of lettuce seedlings were enhanced with increasing the bioremediation time of soils in which they were cultured. An exception was recorded because the VI of letucce grown on polluted soil treated with the consortium was lower at the 14th day (VI=28.5±3.1) than the VI registered at the 7th day (VI=43.0±13.0) in the same condition. Tested seeds were found to be adversely affected by non-remediated soil (control), since the VI was the lowest (VI=8.53±0). Conclusion. Soils planted with maize and inoculated with an actinobacteria consortium showed the highest dissipation of lindane. However, results of phytotoxicity test may be interpreted as an indication that lindane was transformed into toxic intermediates during microbial degradation. Despite of this, results presented here provides evidences that maize plants may attenuate the transient toxic effects of microbial lindane degradation.