Abstract
Microbial degradation plays an essential role in the removal of hydrophobic organic compounds (HOCs) dispersed in soil and sediment, and its performance is greatly affected by mineral particles which regulate HOCs bioavailability by interfacial adsorption. Likewise, bacteria cells attach to the surfaces of mineral particles as well but how bacterial attachment affects biodegradation is largely unknown. Here we report inhibitory effects of goethite and humic acid (HA)-goethite complex addition on microbial degradation of methyl parathion (MP). Using attenuated total reflectance-Fourier transform infrared spectroscopy, we observed that the adhesion of bacterial cells responsible for MP degradation on goethite occurred and the adhesive strength increased over time. We then replaced goethite with phosphate-adsorbed goethite to weaken the goethite-bacteria association and the inhibition of MP biodegradation was alleviated. These results suggested the formation of goethite-bacteria association hinder MP biodegradation. Meanwhile, our results showed that HA coating prevented bacterial attachment on goethite particles along with a drastically increased MP adsorption by goethite. The combined effect would lead to decreased mass fluxes of MP to bacterial cells and could represent another mechanism responsible for the decreased degradation rate observed in the current study.
Highlights
The occurrence and fate of hydrophobic organic compounds (HOCs) such as polycyclic aromatic hydrocarbons and hydrophobic organic pesticides in the environment have received increasing attention because they are potentially toxic, carcinogenic, and persistent to degradation
The properties of bacterial cells and goethite/humic acid (HA)-goethite complex were measured with respect to zeta potential, hydrodynamic diameter, and N2 sorption (Table 1)
The maximum amount of methyl parathion (MP) adsorbed on the HAgoethite complex was 6.7 times higher than that on goethite
Summary
The occurrence and fate of hydrophobic organic compounds (HOCs) such as polycyclic aromatic hydrocarbons and hydrophobic organic pesticides in the environment have received increasing attention because they are potentially toxic, carcinogenic, and persistent to degradation. The presence of sediment particles was found to boost the biodegradation of chrysene and benzo[α]pyrene (Xia and Wang, 2008), and the presence of HA which adsorbed phenanthrene led to an instant increase in its biodegradation rate (Smith et al, 2009). These contradictory results highlighted the complexity of combined studies with solid particles and HOCs, but the role of solid particles in the degradation of HOCs by microorganisms remains uncertain
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