Abstract
E. coli cells overexpressing the enzyme atrazine chlorohydrolase were coated using layer-by-layer self-assembly. The polymeric coating was designed to improve the surface properties of the cells and create positively charged, ecologically safe, bio-hybrid capsules that can efficiently degrade the herbicide atrazine in soils. The physio-chemical properties of the bacteria/polymer interface were studied as a function of the polymeric composition of the shell and its thickness. Characterization of cell viability, enzyme activity, morphology, and size of the bio-capsules was done using fluorescence spectroscopy, BET and zeta potential measurements and electron microscopy imaging. Out of several polyelectrolytes, the combination of polydiallyldimethylammonium chloride and polysodium 4-styrenesulfonate improved the surface properties and activity of the cells to the greatest extent. The resulting bio-hybrid capsules were stable, well-dispersed, with a net positive charge and a large surface area compared to the uncoated bacteria. These non-viable, bio-hybrid capsules also exhibited a kinetic advantage in comparison with uncoated cells. When added to soils, they exhibited continuous activity over a six-week period and atrazine concentrations declined by 84%. Thus, the concept of layer-by-layer coated bacteria is a promising avenue for the design of new and sustainable bioremediation and biocatalytic platforms.
Highlights
In situ bioremediation through bioaugmentation with an inoculum of a pure or mixed culture could be highly efficient and environmentally safe remediation method [1], the introduction of non-indigenous species into soil could pose ecological stress, and the use of genetically modified organisms (GMOs) is often regulatorily restricted [2,3].Catalytic agents for field bioremediation must be stable, anchored to soil particles to avoid being leached out and active under various physical and chemical environmental conditions
LbL assembly was applied to atrazine-degrading bacteria to enhance biodegradation, while creating positively charged, high surface area and non-viable bioparticles, that can be well retained in soils
ATZ degrading bacteria were chosen as a model for active and efficient herbicidebiodegrading agents
Summary
In situ bioremediation through bioaugmentation with an inoculum of a pure or mixed culture could be highly efficient and environmentally safe remediation method [1], the introduction of non-indigenous species into soil could pose ecological stress, and the use of genetically modified organisms (GMOs) is often regulatorily restricted [2,3]. LbL techniques is highly attractive for improving bioremediation platforms, as it provides a well-controlled microenvironment for GMOs and mitigates the ecological risks posed by the addition of non-indigenous microbial population into contaminated sites [21]. It protects the remediating agents within from extreme soil conditions and natural predation, which can hinder bacterial growth or limit the enzymes’ robustness. LbL assembly was applied to atrazine (herbicide)-degrading bacteria to enhance biodegradation, while creating positively charged, high surface area and non-viable bioparticles, that can be well retained in soils. AtzA.on alternating, oppositely charged polyFigure illustration of the biohybrid LbL electrolytes, coating bacteria overexpressing the enzyme AtzA
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