Microorganisms immobilized within poly(vinyl alcohol) cryogels for the biological remediation of organophosphate pesticides and chemical warfare agents.

摘要

Ratification of the Chemical Weapons Convention has focused public attention on international efforts aimed at the destruction of chemical weapons, including sulfur mustard and its precursor, thiodiglycol (TDG), and organophosphate (OP) neurotoxins, as well as the remediation of sites contaminated with these compounds. In addition, widespread use of OP compounds as pesticides and plant growth regulators and their detrimental effects on the environment and humans necessitate the development of effective, environmentally feasible technologies for the degradation of these toxins. Recent progress in the biodegradation of some of these compounds suggests that biological treatment may be the most environmentally and economically feasible strategy for their destruction and for site remediation. However, bioremediative technologies are slower and often lack efficiency, reliability, and predictability. Thus, there is a strong need for improved technologies to enhance biodegradation efficiency.; To this end, Alcaligenes xylosoxidans subsp. xylosoxidans and genetically engineered Escherichia coli expressing organophosphate hydrolase were cryo-immobilized within poly(vinyl alcohol) to form stable, macro-porous biocatalysts which functioned without the addition of nutrients required for cell growth. These immobilized cell systems were capable of effectively degrading two chemical toxins with distinctively different characteristics: TDG, a hydrophilic, water-miscible precursor of sulfur mustard, was degraded by A. xylosoxidans; and coumaphos, a hydrophobic, water-insoluble OP pesticide used in cattle dip, was degraded by the recombinant E. coli strain.; In these studies, biocatalyst conditions for the cryo-immobilized non-growing cell systems were optimized, and degradation efficiencies in the immobilized cell systems were compared with other systems including freely suspended non-growing cells and continuous culture growing cells. This study demonstrated advantages of the cryo-immobilization technology as an effective method to develop a cost-effective and efficient remediation technology.; Additionally, a dynamic diffusion-reaction model for the immobilized non-growing cell systems was developed. Modeling methods used to optimize the biocatalytic efficiency of freely suspended cells were applied to non-growing microbial cells entrapped within a macro-porous carrier. The dynamic model provided an effective and simple way to evaluate the efficiency of the immobilized non-growing cell systems. It utilized the characteristics of freely suspended cells and did not require extensive experimentation to define catalytic behavior inside the biocatalyst.