Distribution Characteristics of Bacterial Communities and Hydrocarbon Degradation Dynamics During the Remediation of Petroleum-Contaminated Soil by Enhancing Moisture Content.

Microorganisms are the driver of petroleum hydrocarbon degradation in soil micro-ecological systems. However, the distribution characteristics of microbial communities and hydrocarbon degradation dynamics during the remediation of petroleum-contaminated soil by enhancing moisture content are not clear. In this study, polymerase chain reaction and high-throughput sequencing of soil microbial DNA were applied to investigate the compositions of microorganisms and alpha diversity in the oil-polluted soil, and the hydrocarbon removal also being analyzed using ultrasonic extraction and gravimetric method in a laboratory simulated ex-situ experiment. Results showed the distribution of petroleum hydrocarbon degrading microorganisms in the petroleum-contaminated loessal soil mainly was Proteobacteria phylum (96.26%)-Gamma-proteobacteria class (90.03%)-Pseudomonadales order (89.98%)-Pseudomonadaceae family (89.96%)-Pseudomonas sp. (87.22%). After 15% moisture content treatment, Actinobacteria, Proteobacteria, and Firmicutes still were the predominant phyla, but their relative abundances changed greatly. Also Bacillus sp. and Promicromonospora sp. became the predominant genera. Maintaining 15% moisture content increased the relative abundance of Firmicutes phylum and Bacillus sp. As the moisture-treated time increases, the uniformity and the richness of the soil bacterial community were decreased and increased respectively; the relative abundance of Pseudomonas sp. increased. Petroleum hydrocarbon degradation by enhancing soil moisture accorded with the pseudo-first-order reaction kinetic model (correlation coefficient of 0.81; half-life of 56 weeks). The richness of Firmicutes phylum and Bacillus sp. may be a main reason for promoting the removal of 18% petroleum hydrocarbons responded to 15% moisture treatment. Our results provided some beneficial microbiological information of oil-contaminated soil and will promote the exploration of remediation by changing soil moisture content for increasing petroleum hydrocarbon degradation efficiency.

Effect of bioaugmentation and biostimulation on hydrocarbon degradation and microbial community composition in petroleum-contaminated loessal soil.

This study assessed the benefits of biostimulation with nitrogen and phosphorous (BS) versus bioaugmentation with native petroleum degrading flora (BA) in terms of petroleum hydrocarbon removal and microbial community structure shift in petroleum-polluted loessal soil. After 12 weeks of remediation, the TPH degradation efficiencies were 28.3% and 13.9% in BS and BA treated soils, respectively. Biostimulation was more effective than bioaugmentation for petroleum hydrocarbon degradation. Soil microbial community composition changed while microbial diversity decreased greatly by bioaugmentation treatment. The inoculum could survive, grow up quickly and become the predominant microorganisms after one week of inoculation. In the biostimulation treatment, microbial community composition is more evenness and richness than in the bioaugmented remediation. The strong positive correlations of the nitrogen and phosphorus with the petroleum hydrocarbon suggest the importance of nutrients for petroleum biodegradation in the contaminated loessal soil. The results indicate that the stabilization and variety of the microbial community structure are essential for the petroleum biodegradation performance. Further engineering is suggested to improve the evenness and richness of the soil microbial community since an abundance of nitrogen and phosphorus nutrients ensures the degraders' activity in the petroleum polluted soil.

[Microbial Community Structure Shift During Bioremediation of Petroleum Contaminated Soil Using High Throughput Sequencing].

The shift in microbial community structure during the bioremediation of oil-polluted soil was analyzed by high-throughput sequencing. The results demonstrated obvious changes in the soil microbial community structure and diversity during bioremediation. The species richness and evenness of the microbial community decreased substantially due to the bioaugmentation treatment. Proteobacteria became the predominant phylum, with a relative increase in abundance from 37.44% to 87.44%. Pseudomonas was the most dominant genus, which increased in abundance from 2.99% to 76.37%. In the biostimulation treated soil, the relative abundance of Proteobacteria decreased from 37.44% to 10.90%, while the phylum Firmicutes increased from 9.16% to 35.32%. At the genus level, the relative abundances of Exiguobacterium and Promicromonospora decreased from 8.49% and 18.96% to 2.19% and 14.97%, respectively. Nocardioides and Bacillus became the dominant genera and increased from 5.56% and 0.29% to 28.95% and 22.70%, respectively. The results indicated that bioaugmentation substantially influenced the soil microbial diversity and community structure. Additionally, the biostimulation treatment maintained the balance in the soil microbial community structure. The stabilization of bacteria community structure is beneficial to petroleum biodegradation in the soil.

Bacterial community shift and hydrocarbon transformation during bioremediation of short-term petroleum-contaminated soil.

A laboratory study was conducted to evaluate the impact of bioaugmentation plus biostimulation (BR, added both nutrients and bacterial consortia), and natural attenuation (NA) on hydrocarbon degradation efficiency and microflora characterization during remediation of a freshly contaminated soil. After 112 days of remediation, the initial level of total petroleum hydrocarbon (TPH) (61,000 mg/kg soil) was reduced by 4.5% and 5.0% in the NA and BR treatments, respectively. Bioremediation did not significantly enhance TPH biodegradation compared to natural attenuation. The degradation of the aliphatic fraction was the most active with the degradation rate of 30.3 and 28.7 mg/kg/day by the NA and BR treatments, respectively. Soil microbial activities and counts in soil were generally greater for bioremediation than for natural attenuation. MiSeq sequencing indicated that the diversity and structure of microbial communities were affected greatly by bioremediation. In response to bioremediation treatment, Promicromonospora, Pseudomonas, Microcella, Mycobacterium, Alkanibacter, and Altererythrobacter became dominant genera in the soil. The result indicated that combining bioaugmentation with biostimulation did not improve TPH degradation, but soil microbial activities and structure of microbial communities are sensitive to bioremediation in short-term and heavily oil-contaminated soil.

[Impacts of Bioremediation on Microbial Communities and Different Forms of Nitrogen in Petroleum Contaminated Soil].

A laboratory study was conducted to investigate the impacts of bioremediation on microbial communities and various nitrogen shifts in petroleum contaminated soil by using GC-MS and Illumia MiSeq technique. Results showed the concentrations of alkane reduced from 25987.8 mg·kg-1 to 12788.6 mg·kg-1, and the concentrations of polycyclic aromatic hydrocarbons (PAHs) decreased from 5322.9 mg·kg-1 to 2917.2 mg·kg-1. Illumia MiSeq results showed that soil microbial communities shifted significantly after remediation, and the relative abundance of some phylum of hydrocarbon degraders (Firmicutes, Bacterodetes), and some genus of degraders (Dietzia, Acinetobacter) increased. Besides, the contents of total nitrogen and ammonia nitrogen increased firstly and then decreased during remediation. However, the contents of nitrate nitrogen decreased at the early stage, and then kept stable in the later stage of remediation. It can be concluded that bioremediation effectively promoted petroleum hydrocarbon degradation, and the different fractional hydrocarbon degradation was related to the relative abundance of hydrocarbon degraders and available nitrogen contents.

[Remediation of Petroleum-Contaminated Soil Using a Bioaugmented Compost Technique].

Bioaugmented compost was created by inoculating petroleum-degrading bacteria into mature compost. The petroleum hydrocarbon degradation efficiencies were investigated by applying this enhanced compost to petroleum-contaminated soil under low temperatures. The results showed that the degrading bacteria can be enriched in the mature compost. After 30 d of remediation, the removal efficiency of TPH, alkanes, and PAHs in the soil was 27.0%, 19.6%, and 10.0%, compared to natural attenuation (CK), which was 4.5%, 9.5%, and 2.3%, respectively. In response to remediation, the relative abundance of Proteobacteria and Actinobacteria phyla decreased from 53.4% and 25.9% to 48.9% and 14.1%, respectively, and Bacteroidetes phylum increased from 5.0% to 24.5%. At the genus level, the relative abundance of Acinetobacter and Pseudomonas increased from 0.02% and 3.4% to 15.2% and 4.6%, respectively. The results indicated that the bioaugmented compost may efficiently facilitate and speed up the bioremediation of petroleum-contaminated soil under low-temperature conditions. Soil microbial diversity and structure of microbial communities are sensitive to the remediation.

Bioremediation of hydrocarbon degradation in a petroleum-contaminated soil and microbial population and activity determination.

Bioremediation of hydrocarbon degradation in petroleum-polluted soil is carried out by various microorganisms. However, little information is available for the relationships between hydrocarbon degradation rates in petroleum-contaminated soil and microbial population and activity in laboratory assay. In a microcosm study, degradation rate and efficiency of total petroleum hydrocarbons (TPH), alkanes, and polycyclic aromatic hydrocarbons (PAH) in a petroleum-contaminated soil were determined using an infrared photometer oil content analyzer and a gas chromatography mass spectrometry (GC-MS). Also, the populations of TPH, alkane, and PAH degraders were enumerated by a modified most probable number (MPN) procedure, and the hydrocarbon degrading activities of these degraders were determined by the Biolog (MT2) MicroPlates assay. Results showed linear correlations between the TPH and alkane degradation rates and the population and activity increases of TPH and alkane degraders, but no correlation was observed between the PAH degradation rates and the PAH population and activity increases. Petroleum hydrocarbon degrading microbial population measured by MPN was significantly correlated with metabolic activity in the Biolog assay. The results suggest that the MPN procedure and the Biolog assay are efficient methods for assessing the rates of TPH and alkane, but not PAH, bioremediation in oil-contaminated soil in laboratory.