Abstract
This is the first investigation of the diversity and distribution of 16S rRNA and phenol monooxygenase (PHE) genes in endophytic and rhizosphere bacteria of plants at sites contaminated with different levels of PAHs. Ten PAHs at concentrations from 34.22 to 55.29 and 45.79 to 97.81 mg·kg−1 were measured in rhizosphere soils of Alopecurus aequalis Sobol and Oxalis corniculata L., respectively. The diversity of 16S rRNA and PHE genes in rhizosphere soils or plants changed with varying PAH pollution levels, as shown based on PCR-DGGE data. Generally, higher Shannon-Weiner indexes were found in mild or moderate contaminated areas. A total of 82 different bacterial 16S rRNA gene sequences belonging to five phyla; namely, Acfinobacteria, Proteobacteria, Chloroflexi, Cyanophyta, and Bacteroidetes, were obtained from rhizosphere soils. For the 57 identified PHE gene sequences, 18 were excised from rhizosphere bacteria and 39 from endophytic bacteria. The copy numbers of 16S rRNA and PHE genes in rhizosphere and endophytic bacteria varied from 3.83 × 103 to 2.28 × 106 and 4.17 × 102 to 1.99 × 105, respectively. The copy numbers of PHE genes in rhizosphere bacteria were significantly higher than in endophytic bacteria. Results increase our understanding of the diversity of rhizosphere and endophytic bacteria from plants grown in PAH-contaminated sites.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are a class of typical organic pollutants comprised of two or more benzene rings[1]
Pritchina et al.[22] used a terminal restriction fragment length polymorphism (TRFLP) technique to investigate the rhizosphere bacterial communities of four types of plant grown in the presence of different PAH-contaminated soils; the results showed that the level of PAH pollution had a more significant influence on the rhizosphere bacterial community structure than did the type of host plant
NAP and PHA were the primary PAHs in the rhizosphere soils of both A. aequalis and O. corniculata, accounting for 76.51 to 76.97% and 65.35 to 86.87% of the total concentrations, respectively
Summary
Polycyclic aromatic hydrocarbons (PAHs) are a class of typical organic pollutants comprised of two or more benzene rings[1]. Rhizospheric and endophytic bacteria have PAH biodegradation potential and are widely distributed in the organs and rhizosphere of plants growing in PAH-polluted sites[6,7,8,9]. Investigating the ecological structure and diversity of these endophytic bacteria and PAH-degrading genes in contaminated sites is important for their application in biological remediation. 45.79 ± 5.49c distribution and community structure of endophytic bacteria in plants from PAH-contaminated sites[13], but we did not explore PAH-degrading genes at such sites. Investigations of PAH-degrading genes as well as the diversity and distribution of rhizospheric and endophytic bacteria in PAH-contaminated sites is important; this is a prerequisite for use of PAH-degradable bacteria to eliminate soil PAH contamination and reduce plant PAH risk
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