Microbial Mechanisms Controll the Rhizosphere Effect of Ryegrass on Degradation of Polycyclic Aaromatic Hydrocarbons
The phyto-remediation of soil polluted by Polycyclic Aromatic Hydrocarbons (PAHs) depends on plant-microbe interactions in the rhizosphere. The rhizospfere environment promotes soil microbial biomass, activity and diversity. PAH-ring hydroxylating dioxygenase (PAH-RHDα) is the core enzyme in PAHs degradation. The research on PAH-RHDα will provide theoretical base for the responses of microbes to PAHs.
Led by Prof. GONG Zongqiang, Dr. GUO Meixia and coworkers from the Research Group of Soil Pollution Ecology, Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences, conducted a rhizo-box experiment planted with ryegrass in an aged PAH-contaminated agricultural soil for 60 days. Mycobacterium sp. was inoculatedinto the specially constructed rhizo-box.
The removal of PAHs and dynamics of active bacterial community structure in rhizosphere and non-rhizosphere soils during phytoremediation were compared using HPLC and cDNA-based DGGE analysis, respectively.
The rhizosphere effect of ryegrass on the abundance (DNA) and activity (RNA) of total bacteria and PAH-degraders containing functional PAH-RHDα genes were quantified through real-time PCR and reverse transcription-PCR (RT-PCR), respectively.
In addition, cloning and sequencing were used to investigate the diversity of PAH-RHDα genes in the soil.
The results show that the soil contained Gram-positive (GP) and Gram-negative (GN) bacteria that degrade PAHs.The RHDα genes includednidA3, pdoA, nahAc and phnAc.
In the ryegrass rhizosphere, the GP bacteria dominated the PAH degrading bacteria. The growth of ryegrass increased the diversity of functional bacteria in 10 days and the promoting effect was selective. The effect of ryegrass and Mycobacteria promoted PAH degradation in the agricultural soil by altering microbial community structure, increasing bacteria diversity, and stimulating the expression of RHDα genesduring the 60-day inoculation.
The work deepens our understanding of plant-microbial interactions in the bio-remediation of soils, provides theoretic bases for the ryegrass rhizosphere effect on PAHs degradation, and would promote the further development of theory and technology in remediation of soil polluted by PAHs.
The results were published in Soil Biology & Biochemistry entitled "Microbial mechanisms controlling the rhizosphere effect of ryegrass on degradation of polycyclic aromatic hydrocarbons in an aged-contaminated agricultural soil".
The work was funded by NNSAFS and The Key Lab of Pollution Ecology and Environmental Engineering, IAE.
Fig 1. Residual total PAH concentrations in microcosms over a 60-day incubation. control: unplanted soil; M: unplanted soil inoculated with Mycobacterium sp.; R-: nonrhizosphere soil; R+: rhizosphere soil; MR-: non-rhizosphere soil inoculated with Mycobacterium sp.; MR+: rhizosphere soil inoculated with Mycobacterium sp. Different lowercase letters at the same time point show significant difference at P < 0.05 between treatments, ANOVA with LSD test, the same as below. (Image by GUO Meixia).
Publication Name:GUO Meixia et al.