Phosphotriesterase-Like Lactonase Immobilized on Zeolites for Pesticides Degradation

Pesticides were and are extensively used in agriculture for controlling the spread of unwanted insects or weeds. The extensive use of pesticides causes serious environmental concerns; in fact, only 5% or less of the applied pesticides reach the target organisms which resulted in contamination of soil and water. Their continuous use brought an accumulation of pesticides and their residues in environment, endangering the populations by their varied toxicity [1]. Among the various groups of pesticides, organophosphates (OPs) are one of the most widely used types [2]. The current methods for the OPs compounds detoxification are harmful and determine serious environmental consequences. Therefore, the use of enzymes for the detection and decontamination of organophosphate agents has received considerable attention [2, 3]. Many enzymes catalyze the hydrolysis of the OPs among which the phosphotriesterases (PTE; EC 3.1.8.1) [4, 5] and PTE-like lactonases (PLL) [6]. Some of them are commercially available and were employed to purify OP-contaminated water. However, the main problem associated with the use of these enzymes is their low stability in solution [7].Usually, the enzymes are immobilized on inorganic or organic supports for improving their stability [8-10]. In addition, immobilization process facilitates the enzyme re-use and also leads to an easier separation of the enzyme from the reaction mixture, provides the control of the reaction time and reduces the enzyme loss in the product stream [11]. Among the various inorganic supports, zeolites have attracted significant attention for enzyme immobilization having remarkable properties: high surface area for high enzyme loadings, high chemical and mechanical stability [12]. Zeolites (alumino-silicate materials with well-defined pore size at molecular scale) are cost effective and non-toxic with respect to the health issues [13]. Considering these characteristics, they are suitable candidates for different applications such as water purification and softening, separation processes and sensors [14, 15] and for immobilization of enzymes [11, 16-18].

The topic of this work is the development of environmental-friendly materials for the treatment of waste water and for the remediation of contaminated sites. In particular, the study was focused on the covalent immobilization of a mutated version of the PLL from SsoPox namely SsoPox W263F on the zeolite surface using the glutaraldehyde as cross linker. The immobilized enzyme was used for performing preliminary studies on the organophosphate pesticide (paraoxon ethyl) degradation.