Jinyu Hou

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.

Estimating cadmium availability to the hyperaccumulator Sedum plumbizincicola in a wide range of soil types using a piecewise function

Estimating the bioavailability and predicting the uptake of metals to hyperaccumulators is very important in developing the field application of phytoextraction. A pot experiment was conducted using 108 agricultural soils covering a wide range of soil properties by the cadmium (Cd) hyperaccumulator Sedum plumbizincicola. The contributions of a range of soil properties to Cd uptake were quantified. Soil total, soluble, CaCl2-extractable and diffusive gradients in thin films (DGT)-extractable Cd concentrations (Cdtotal, Cdsoln, CdCaCl2 and CdDGT) were used to estimate Cd bioavailability and predict shoot Cd concentration (Cdshoot) using a piecewise function. Cdtotal and pH were the two major contributors to Cd uptake. Cdshoot showed a logarithmic increase with Cdtotal from 0.30 to 10.0 mg kg-1 but no further increase when Cd levels exceeded 10 mg kg-1. Soil pH had a discernible negative effect on Cd bioavailability from pH 5.5 to 7.5 but a weak influence at pH < 5.5 or pH > 7.5. This indicates that the optimum pH for phytoextraction with S. plumbizincicola was ~5.5 and lower pH produced little increase in shoot Cd uptake. DGT gave the best estimation of Cd bioavailability across all the data. When Cdtotal > 10 mg kg-1, none of the four measures was accurate enough to predict Cdshoot but when pH > 7.5 all the four measures were well correlated with Cdshoot. Piecewise equations in different ranges of Cdtotal or pH significantly improved the prediction of Cdshoot compared with the global equations derived from all the data. Compared with the piecewise equations, when pH > 7.5 Cdshoot was greatly overestimated with the global equation of Cdtotal. Our study provides useful information on the soils in which phytoextraction with S. plumbizincicola is feasible in the field. CAPSULE Cd availability to S. plumbizincicola was estimated by a piecewise function in soils with wide ranges of total Cd concentration and pH.

Modulation of the efficiency of trace metal phytoremediation by Sedum plumbizincicola by microbial community structure and function

AimsRecent research on the rhizosphere microbiome indicates that plants may benefit more from microbial communities than from individual members in a community. The link between soil microbiome and plant performance remains poorly understood during trace metal phytoremediation by hyperaccumulator plants. The effect of different microbiomes on the cadmium (Cd)/zinc (Zn) phytoextraction efficiency of Sedum plumbizincicola was therefore explored.MethodsDifferent microbiomes were set up using γ-irradiation and vancomycin addition and a pot experiment was conducted. The microbial communities were characterized using high-throughput sequencing and their functions were predicted.ResultsPlant Cd and Zn contents in the vancomycin-amended treatment were about 38–46% and 35%–53% respectively lower than those in the other treatments. Bacterial composition and diversity were substantially changed by γ-irradiation and vancomycin addition but plant trace metal accumulation did not change subsequently. The bacterial functional profiles were very different following treatment with vancomycin compared with the other treatments at KEGG orthology hierarchy level 3. Genes related to up-regulated biofilm formation and down-regulated siderophore synthesis may partly contribute together to the low plant trace metal accumulation following vancomycin treatment.ConclusionsSpecific bacterial community function rather than bacterial community diversity and composition may affect trace metal uptake by hyperaccumulator plants.