Qingling Wang

PGPR enhanced phytoremediation of petroleum contaminated soil and rhizosphere microbial community response

The aim of this study was to investigate petroleum phytoremediation enhancement by plant growth promoting bacteria (PGPR), specifically the correlation between petroleum hydrocarbon fractions and bacterial community structure affected by remediation and PGPR inocula. Aged petroleum contaminated soil was remediated by tall fescue (Testuca arundinacea L.) inoculated with two PGPR strains. Hydrocarbon degradation was measured by GC-MS (Gas-chromatography Mass-spectrometer) based on carbon fraction numbers (C8-C34). Changes in bacterial community structure were analyzed by high-throughput pyrosequencing of 16s rRNA. PGPR inoculation increased tall fescue biomass and petroleum hydrocarbons were removed in all the treatments. Maximum hydrocarbon removal, particular high molecular weight (C21-C34) aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs), was observed in tall fescue inoculated with PGPR. The relative abundance of phyla γ-proteobacteria and Bacteroidetes increased after different treatments compared with controls. Moreover, a bacterial guild mainly comprising the genera Lysobacter, Pseudoxanthomonas, Planctomyces, Nocardioides, Hydrogenophaga, Ohtaekwangia was found to be positively correlated with C21-C34 petroleum hydrocarbons fractions removal by RDA analysis, implying that petroleum degradation was unrelated to bacterial community diversity but positively correlated with specific petroleum degraders and biosurfactant producers.

Isolation and characterization of plant growth-promoting rhizobacteria and their effects on phytoremediation of petroleum-contaminated saline-alkali soil

This study aimed to isolate promising halotolerant and alkalotolerant plant growth-promoting rhizobacteria and to study their effects on the growth of tall fescue and phytodegradation efficiency in a petroleum-contaminated saline-alkaline soil. A total of 115 PGPR strains were isolated from the rhizosphere of tall fescue grown in petroleum-contaminated saline-alkaline soils. Of these, 5 strains indicating 1-aminocyclopropane-l-carboxylic acid deaminase activity>1.0M α-KB mg(-1)h(-1) were selected for further studies. The isolate D5A presented the highest plant-growth-promoting activity and was identified as Klebsiella sp. It grew well on the Luria-Bertani medium containing 9% NaCl and at a pH range of 4-10. A pot experiment was then conducted to study the effect of isolates on phytoremediation. The results showed that inoculation of D5A promoted tall fescue growth and enhanced remediation efficiency in petroleum-contaminated saline-alkaline soil.

Whole genome analysis of halotolerant and alkalotolerant plant growth-promoting rhizobacterium Klebsiella sp. D5A.

This research undertook the systematic analysis of the Klebsiella sp. D5A genome and identification of genes that contribute to plant growth-promoting (PGP) traits, especially genes related to salt tolerance and wide pH adaptability. The genome sequence of isolate D5A was obtained using an Illumina HiSeq 2000 sequencing system with average coverages of 174.7× and 200.1× using the paired-end and mate-pair sequencing, respectively. Predicted and annotated gene sequences were analyzed for similarity with the Kyoto Encyclopedia of Genes and Genomes (KEGG) enzyme database followed by assignment of each gene into the KEGG pathway charts. The results show that the Klebsiella sp. D5A genome has a total of 5,540,009 bp with 57.15% G + C content. PGP conferring genes such as indole-3-acetic acid (IAA) biosynthesis, phosphate solubilization, siderophore production, acetoin and 2,3-butanediol synthesis, and N2 fixation were determined. Moreover, genes putatively responsible for resistance to high salinity including glycine-betaine synthesis, trehalose synthesis and a number of osmoregulation receptors and transport systems were also observed in the D5A genome together with numerous genes that contribute to pH homeostasis. These genes reveal the genetic adaptation of D5A to versatile environmental conditions and the effectiveness of the isolate to serve as a plant growth stimulator.

Collection and analysis of root exudates of Festuca arundinacea L. and their role in facilitating the phytoremediation of petroleum-contaminated soil

Background and aimsThe objectives of this study were to elucidate the mechanisms of interaction between root exudates of tall fescue and functional bacteria associated with petroleum degradation and whether components of the exudates can enhance petroleum removal from soil.MethodsRoot exudates of tall fescue were collected through a continuous root exudate trapping system and identified by GC-MS. Chemotaxis, swarming, and in vitro assay were conducted to assess the effects of the organic acids of root exudates on Klebsiella sp. D5A (plant growth promoting rhizobacterium), Pseudomonas sp. SB (biosurfactant producing bacterium), and Streptomyces sp. KT (petroleum-degrading bacterium). A pot experiment with organic acid amendment was conducted to study the effects of these components of root exudates on petroleum remediation. Microbial physiological metabolisms affected by organic acids were tested using Biolog Eco plates.ResultsPalmitic acid was found to be most effective in promoting D5A colonization on tall fescue. ρ-Hydroxybenzoic and palmitic acids significantly stimulated the growth of strains D5A, SB, and KT. Furthermore, palmitic acid amendment significantly enhanced petroleum removal in pot experiment.ConclusionsPalmitic acid was the critical organic acid to facilitate petroleum removal during phytoremediation. These findings provide insight into the mechanisms by which tall fescue enhances the degradation of petroleum.

Changes in the abundance and structure of bacterial communities under long-term fertilization treatments in a peanut monocropping system

Background and aimsPeanut yield and quality are seriously compromised by continuous monoculturing in the red soil region of southern China. Monoculturing can cause soil degradation and an increase in soil-borne diseases. This research aimed to investigate the influence of long-term peanut monocropping and different fertilization treatments on peanut growth, soil physical and chemical properties and soil microbial community.MethodsA long-term fertilization experiment established in 1996 was utilized to examine the effect of various fertilization treatments including chemical and organic fertilizers treatments. Deep 16S rRNA gene pyrosequencing highlighted changes in the abundance and structure of bacterial communities, especially of the pathogenic and beneficial bacterial communities in long term chemical fertilizer treatment in comparison to the organic manure treatment.ResultsChemical fertilizer treatment causes a shift in bacterial community structure and decrease in diversity under the long-term monocropping in comparison to organic fertilizer. The abundance of the bacterial pathogen Ralstonia solanacearum, a causative agent of peanut wilt, was found to be associated with a loss of community diversity and loss of the peanut yield.ConclusionsThe organic fertilizers more effectively increase microbial diversity in the soil and changed the community structure. Long-term use of the chemical fertilizer leads to a decrease in microbial diversity of the soil and an increase in R. solanacearum with associated increase of peanut wilt. The potential decrease in diversity and competition between the bacterial community and the pathogen may be a contributing factor to increased disease during long-term chemical fertilizer use.

Response of soil enzymes and microbial communities to root extracts of the alien Alternanthera philoxeroides

ABSTRACT Alternanthera philoxeroides is an alien invasive species, which can cause substantial damage to the local ecosystem by secreting allelochemicals. The objective of the present study was to appraise the effects of root extracts of the invasive plant Alternanthera philoxeroides on soil enzyme and native microbial community. Urease activity was measured using the phenol sodium hypochlorite colorimetric method, sucrase activity was determined by 3, 5-dinitrosalicylic acid colorimetric method, catalase activity was determined using the KMnO4 titration method and alkaline phosphatase activity was determined by the disodium phenyl phosphate colorimetric method. The soil microbial community was investigated by pyrosequencing of the 16S rRNA gene. Results showed that the alkaline phosphatase, sucrase and urease activities were all significantly lower than that of the control treatment. The structure of the soil microbial community in the treatments with root extracts addition clearly differed from that of the control treatment. The result showed that the relative abundance of microorganism decreased including Burkhholderia, Gp6, Gp1 and Gp4 in the applied treatments at genus level as compared to control treatment. Hence, we inferred that A. philoxeroides could inhibit the growth of native plant species through toxic effects on soil enzyme activities and the microbial community.