Effect of characteristics of phenanthrene-degrading bacteria Pseudomonas sp. JM2-gfp on biofilm formation and its colonization on plant root surface

Abstract:

[Background] Polycyclic aromatic hydrocarbons (PAHs) accumulated in agricultural soils are threatening human health and ecosystem via food chain. The strategy to impede PAHs entrance by biofilm formation of degrading bacteria on the root surface is economically feasible. Bacteria cell properties are the key factors determining its adhesion and initial formation of the biofilm. [Objective] Our study aims to investigate the biofilm formation process and identify the features of a phenanthrene degrading bacterium Pseudomonas sp. JM2-gfp influencing on the cell adhesion and the biofilm formation, to observe its colonization on the wheat root surface, and finally to provide references for building a control barrier in the soil-rhizosphere system.[Methods] Methods of petri dish culture observation, crystal violet stain, and contact angle assay were used to determine the cell characteristics of JM2-gfp. Hydroponic culture of plant was used to generate the biofilm formation. The structural features of the biofilm were observed and analyzed by a confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM). [Results] The strain Pseudomonas sp. JM2-gfp has a flagella structure and hydrophobic cell wall, as well as strong motility, initial adhesion, self-aggregation ability. It showed good biofilm-forming abilities and phenanthrene-degrading performance. Compared with planktonic bacteria, our biofilms can degrade phenanthrene within 48 hours by 2.5 times. The film formation process presented obvious periodic changes, and the amount of the biofilm reached the maximum at the second day. The thickness of the biofilm within 2 days was about 32.8 μm, and a variety of extracellular polymeric substances (EPS) were secreted on the biofilm, containing carbohydrate at the concentration of 74.68 μg/mL and protein 211.9 μg/mL, respectively. After 4 days of co-cultivation of wheat roots and JM2-gfp, a stable biofilm was formed by JM2-gfp on the root surface, and further colonized the roots, stems and leaf tissues. [Conclusion] The phenanthrene degrading bacterium Pseudomonas sp. JM2-gfp can form stable biofilms and enhance its degradation abilities. The formation of biofilm on the root surface provides an alternative approach in future applications to prevent organic pollutants entering into the crops.