Biodégradation de quelques composés organiques volatils et certains pesticides par des actinomycètes provenant d’un sol agricole et de boues activées.

Abstract

From an agricultural soil sample from the region of Ain M'Lila and a sample of activated sludge from the Ibn Ziad-Constantine wastewater treatment plant, we isolated respectively 80 and 18 phenotypically different actinobacteria. The samples in question were the subject of a physic-chemical analysis. Firstly, we conducted a functional study by testing these isolates on a minimum solid medium supplemented with 500 mg/L of different pesticides most commonly used in Algeria, namely the Ortiva and Rodazime fungicides. Insecticides like Karate, Phoenix, Dursban and Cypermethrin. Herbicides in several commercial forms such as Mamba, Zoom, Glyphosate, Herbasate, Roundup, Traxos and Axial to characterize their abilities to use these pesticides as the sole source of carbon and energy. The results showed that the majority of isolates had the ability to degrade these synthetic compounds. Thus, in this thesis work, we have been interested in testing the ability of these isolates to degrade BTEX, which is an important family of volatile organic compounds. They contaminate various ecosystems such as air, surface water, groundwater and soil. These compounds have very toxic effects on humans and animals. Several microorganisms have been tested for their ability to degrade BTEX. Others have unfortunately been neglected despite their interesting metabolic and physiological aptitudes. In the present study, we tested the degradation of these compounds by isolated actinomycetes taken individually or in consortia. The results of growth and degradation kinetics showed that 20 actinobacteria and 2 reconstituted consortia were able to use at least one BTEX compound as the sole source of carbon and energy. Of these, four from activated sludge and one from agricultural soils degraded all these volatile organic compounds in vitro under aerobic conditions at concentrations ranging from 1400 to 1500 mg/L in 72 to 96 h of incubation. The second part of this work aimed to identify active isolates. The physiological study informed us about the remarkable metabolic diversity of the isolates tested. In addition, a taxonomic study was conducted by sequencing 16S rRNA of 25 strains. This identification showed that twenty-one of these isolates belonged to the genus Streptomyces and three to the genus Nocardia. This result is very encouraging and shows that actinomycetes that come from sewage treatment plants and agricultural soils have the ability to biodegrade these organic volatil compounds and pesticides. The isolated strains are excellent candidates for bioremedion of terrestrial and aquatic sites polluted by these xenobiotics.