Characterization of Biofilm Formed by Phenanthrene-Degrading Bacteria on Rice Root Surfaces for Reduction of PAH Contamination in Rice.

Xiaorong Gao,Yuman Zhou

doi:10.3390/ijerph16112002

Abstract

One effective method in to reduce the uptake of organic contaminants by plants is the development of a root barrier. In this study, the characterization of biofilm structure and function by phenanthrene-degrading Pseudomonas sp. JM2-gfp on rice root surfaces were carried out. Our results showed that root surfaces from three rice species, namely Liaojing401, Koshihikari, and Zhenzhuhong all present hydrophobicity and a high initial adhesion of strain JM2-gfp. Matured robust biofilm formation occurred at 48 h on the root surfaces. The biofilm exhibited cell dense aggregates and biomass embedded in the extracellular polymeric substance (EPS) matrix. EPS composition results showed that the proteins, carbohydrates, lipids and nucleic acids are produced in the biofilm, while the content varied with rice species. Under the initial concentration of phenanthrene 50 mg·L−1, the residual phenanthrene in plant roots from ‘Zhengzhuhong’, ‘Koshihikari’ and ‘Liaojing401’ with biofilm mediated were significantly decreased by 71.9%, 69.3% and 58.7%, respectively, compared to those without biofilm groups after 10 days of exposure. Thus, the biofilm colonized on roots plays an important role of degradation in order to reduce the level of phenanthrene uptake of plants. Thereby, the present work provides significant new insights into lowering the environmental risks of polycyclic aromatic hydrocarbons (PAHs) in crop products from contaminated agriculture soils.

Highlights

With polycyclic aromatic hydrocarbons (PAHs) in agriculture, soil contamination is of great worldwide concern because of their persistent organic lethal nature [1]
The structures may facilitate the formation of biofilm by the phenanthrene-degrading bacteria JM2-gfp as they provide more anchoring points for the adhesion of bacteria
Our results indicated that the hydrophobicity of the root surfaces affected the content of proteins and carbohydrates in the extracellular matrix secreted from phenanthrene-degrading bacteria, with underlying mechanisms left to be further explored

Summary

Introduction

With polycyclic aromatic hydrocarbons (PAHs) in agriculture, soil contamination is of great worldwide concern because of their persistent organic lethal nature [1]. Crops grown in PAH-contaminated soil uptake PAHs (phenanthrene and pyrene) that accumulate in the edible parts, posing a substantial threat to human health. Numerous strains of microorganisms with the capability to degrade PAHs have been successfully isolated [3]. The low bioavailability caused by their poor survival rate in soil has greatly limited the application of degrading-bacteria in the bioremediation of PAHs. Recent studies have highlighted that certain PAH-degrading microorganisms are able to form a biofilm on the surfaces of plant roots, leading to the accumulation of high biomass and its long-term survival for continuous degradation in rhizosphere soil, reducing the absorption of PAHs by roots and ensuring the safety of crop products [4,5]. To our knowledge, in situ PAH-degrading biofilm on the root surfaces has not been observed

Methods

Results

Conclusion