Lindane removal by Streptomyces sp. strains immobilized in agar and PVA-alginate

Abstract

γ-Hexachlorocyclohexane (γ-HCH) or lindane is a chlorinated pesticide, which initially played important roles in the control of pests and disease vectors. Nowadays it is well established that it is a toxic, carcinogenic and persistent compound which not only accumulates in animals and plants tissues, but also persist in the environment for long periods. There has been much work on γ-HCH biodegradation. Bacteria and consortia of bacteria capable of degrading lindane under aerobic and anaerobic conditions have been described. Immobilization techniques are gaining importance in bioremediation because of their advantages such as protection of the cells against the pesticide toxicity, reuse of the cells and the facility to recover them from the system. The aim of this work was to evaluate the ability of streptomycetes strains immobilized in agar cubes and polyvinyl alcohol-alginate beads to remove lindane in a liquid system. For this purpose, four streptomycetes strains (Streptomyces sp. A2, A5, A11 and M7) previously selected because of their ability to degrade γ -HCH in pure and mixed cultures, were pre-cultivated in TSB medium for 72 h. Biomass pellets were individually entrapped using: a) 3% agar cubes and b) PVA-alginate beads. 5 g of cubes or beads were put into an Erlenmeyer containing 100 mL liquid minimal medium (MM) supplemented with lindane (1.66 mg L-1) as carbon source. After 96 h of incubation, the cells were collected to determine microbial growth by estimating the colony forming units (CFU g-1) and supernatant samples were taken to determine residual lindane concentration by gas chromatography. The four studied strains were able to grow in MM supplemented with lindane as sole carbon source. All of them showed lower growth values when they were immobilized in PVA-alginate beads than in agar cubes. Maximal growth (1.35 x 10 8 CFU g-1) was obtained by Streptomyces sp. A11 immobilized in agar cubes. However γ-HCH removal was more efficient when actinobacteria were immobilized in PVA-alginate beads, showing Streptomyces sp. M7 the greatest lindane removal ability, while no lindane removal was observed with the agar-entrapped bacterial strain, Streptomyces sp. A11. The results showed that PVA-alginate can be used as potential actinobacteria immobilization matrix for lindane bioremediation.