Comparison of mono-rhamnolipids and di-rhamnolipids on microbial enhanced oil recovery (MEOR) applications

Rhamnolipids (RMLs) have more effectiveness for specific uses according to their homologue proportions. Thus, the novelty of this work was to compare mono-RMLs and di-RMLs physicochemical properties on microbial enhanced oil recovery (MEOR) applications. For this, RML produced by three strains of Pseudomonas aeruginosa containing different homologues proportion were used: a mainly mono-RMLs producer (mono-RMLs); a mainly di-RMLs producer (di-RMLs), and the other one that produces relatively balanced amounts of mono-RML and di-RML homologues (mono/di-RML). For mono-RML, the most abundant molecules were Rha-C₁₀C₁₀ (m/z 503.3), for di-RML were RhaRha-C₁₀C₁₀ (m/z 649.4) and for Mono/di-RML were Rha-C₁₀C₁₀ (m/z 503.3) and RhaRha-C₁₀C₁₀ (m/z 649.4). All RMLs types presented robustness under high temperature and variation of salinity and pH, and high ability for oil displacement, foam stability, wettability reversal and were classified as safe for environment according to the European Union Directive No. 67/548/EEC. For all these properties, it was observed a highlight for mono-RML. Mono-RML presented the lowest surface tension (26.40 mN/m), interfacial tension (1.14 mN/m), and critical micellar concentration (CMC 27.04 mg/L), the highest emulsification index (EI₂₄ 100%) and the best wettability reversal (100% with 25 ppm). In addition, mono-RML showed the best acute toxicity value (454 mg/L), making its application potential even more attractive. Based on the results, it was concluded that all RMLs homologues studied have potential for MEOR applications. However, results showed that mono-RML stood out and have the best mechanism of oil incorporation in micelles due their most effective surface-active physicochemical features.     

水淹对三峡库区岸生植物秋华柳(Salix variegata Franch.)存活和恢复生长的影响

植物在水淹后的存活和恢复生长状况可以衡量其对水淹的耐受能力,为了解三峡库区岸生植物秋华柳(Salix variegata Franch.)的水淹耐受能力,研究了长期水淹条件下秋华柳植株的存活和恢复生长状况.实验设置了3个水淹深度:对照,水淹根部(植株置于水中,仅地下部分被淹没)和水淹2m(植株置于水中,顶部距水面2m),6个水淹时间:20d,40d,60d,90d,120d和180d.研究结果表明:(1)水淹对秋华柳植株存活率的影响较小.水淹根部处理的植株在水淹180d后,存活率仍为100%,水淹2m处理的植株在水淹120d后,存活率也为100%,直到180d后,存活率才下降为0.(2)水淹后,秋华柳植株仍然可以进行恢复生长,表现出很强的恢复生长能力,但因水淹处理的不同,其恢复生长存在差异.随着水淹时间的延长,秋华柳植株出水后到开始恢复生长之前所需的时间增加,但所有水淹处理的植株在水淹结束后一周内都可以开始恢复生长.在相同水淹时间处理下,水淹处理的秋华柳植株在恢复生长期间的相对生长速率都高于对照植株,水淹40d,60d,90d后,水淹2m的秋华柳植株分别比对照植株高57.8%,143.4%,130.4%.水淹结束时,秋华柳地上部分生物量随水淹深度的不同而不同,水淹根部处理的植株几乎与对照植株无显著差异,水淹2m处理的植株都低于对照植株.水淹结束后,不同处理的秋华柳植株生长2个月后的地上部分生物量与其在水淹结束时不同处理植株地上部分生物量的变化趋势相似.本研究表明,秋华柳在长时间的水淹后具有很高的存活率,并可以进行很好的恢复生长,表现出较强的水淹耐受能力,可以考虑将其应用于三峡库区消落区的植被构建.     

Impact of an indigenous microbial enhanced oil recovery field trial on microbial community structure in a high pour-point oil reservoir

Based on preliminary investigation of microbial populations in a high pour-point oil reservoir, an indigenous microbial enhanced oil recovery (MEOR) field trial was carried out. The purpose of the study is to reveal the impact of the indigenous MEOR process on microbial community structure in the oil reservoir using 16Sr DNA clone library technique. The detailed monitoring results showed significant response of microbial communities during the field trial and large discrepancies of stimulated microorganisms in the laboratory and in the natural oil reservoir. More specifically, after nutrients injection, the original dominant populations of Petrobacter and Alishewanella in the production wells almost disappeared. The expected desirable population of Pseudomonas aeruginosa, determined by enrichment experiments in laboratory, was stimulated successfully in two wells of the five monitored wells. Unexpectedly, another potential population of Pseudomonas pseudoalcaligenes which were not detected in the enrichment culture in laboratory was stimulated in the other three monitored production wells. In this study, monitoring of microbial community displayed a comprehensive alteration of microbial populations during the field trial to remedy the deficiency of culture-dependent monitoring methods. The results would help to develop and apply more MEOR processes.     

Monitoring exogenous and indigenous bacteria by PCR-DGGE technology during the process of microbial enhanced oil recovery

A field experiment was performed to monitor changes in exogenous bacteria and to investigate the diversity of indigenous bacteria during a field trial of microbial enhanced oil recovery (MEOR). Two wells (26-195 and 27-221) were injected with three exogenous strains and then closed to allow for microbial growth and metabolism. After a waiting period, the pumps were restarted and the samples were collected. The bacterial populations of these samples were analyzed by denaturing gradient gel electrophoresis (DGGE) with PCR-amplified 16S rRNA fragments. DGGE profiles indicated that the exogenous strains were retrieved in the production water samples and indigenous strains could also be detected. After the pumps were restarted, average oil yield increased to 1.58 and 4.52 tons per day in wells 26-195 and 27-221, respectively, compared with almost no oil output before the injection of exogenous bacteria. Exogenous bacteria and indigenous bacteria contributed together to the increased oil output. Sequence analysis of the DGGE bands revealed that Proteobacteria were a major component of the predominant bacteria in both wells. Changes in the bacteria population in the reservoirs during MEOR process were monitored by molecular analysis of the 16S rRNA gene sequence. DGGE analysis was a successful approach to investigate the changes in microorganisms used for enhancing oil recovery. The feasibility of MEOR technology in the petroleum industry was also demonstrated.     

Microbial response to reinjection of produced water in an oil reservoir

The microbial response to produced water reinjection (PWRI) in a North Sea oil field was investigated by a combination of cultivation and culture-independent molecular phylogenetic techniques. Special emphasise was put on the relationship between sulphate-reducing bacteria (SRB) and nitrate-reducing bacteria (NRB), and results were used to evaluate the possibility of nitrate treatment as a souring management tool during PWRI. Samples were collected by reversing the flow of the injection water, which provided samples from around the injection area. The backflowed samples were compared to produced water from the same platform and to backflowed samples from a biocide-treated seawater injector, which was the previous injection water treatment of the PWRI well. Results showed that reinjection of produced water promoted growth of thermophilic SRB. Thermophilic fatty acid oxidising NRB and potential nitrate-reducing sulphide-oxidising bacteria were also found. The finding of thermophilic NRB makes nitrate treatment during PWRI possible, although higher nitrate concentration will be necessary to compensate for the increased SRB activity.     

Optimization of the anaerobic treatment of a waste stream from an enhanced oil recovery process

The aim of this work was to optimize the anaerobic treatment of a waste stream from an enhanced oil recovery (EOR) process. The treatment of a simulated waste water containing about 150 mg chemical oxygen demand (COD)/L of total petroleum hydrocarbons (TPH) and the saturation level of CO₂ was evaluated. A two-step anaerobic system was undertaken in the mesophilic temperature range (30-40 °C). The method of evolutionary operation EVOP factorial design was used to optimize pH, temperature and organic loading rate with the target parameters of CO₂ reduction and CH₄ production in the first reactor and TPH removal in the second reactor. The results showed 98% methanogenic removal of CO₂ and CH₄ yield of 0.38 L/gCOD in the first reactor and 83% TPH removal in the second reactor. In addition to enhancing CO₂ and TPH removal and CH₄ production, application of this method showed the degree of importance of the operational variables and their interactive effects for the two reactors in series.     

Microbiological and production characteristics of the Dagang high-temperature heavy oil reservoir (block no. 1) during trials of the biotechnology for enhanced oil recovery

Microbiological and biogeochemical data on the Kongdian bed (block no. 1) of the Dagang high-temperature oilfield during trials of the biotechnology for enhanced oil recovery are reported. Oil-bearing horizons of block no. 1 are characterized by high temperature (56.9–58.4°C), complex geological conditions, and heavy oil (density 0.966–0.969 g/cm³). The biotechnology implied injecting oxygen as an air-water mixture or H₂O₂ together with aqueous solution of nitrogen and phosphorus mineral salts through injection wells in order to activate the oilfield microbial community. In the course of trials, an increase in abundance of aerobic and anaerobic microorganisms was revealed, as well as increased methanogenesis rate in formation water. Microbial oxidation of heavy oil resulted in increased concentration of mineral carbonates dissolved in formation water, changes in the stable carbon isotopic composition δ¹³C/Σ(CO₂ + HCO₃ ^- + CO₃ ^2-), formation of biosurfactants, and decreased interfacial tension of formation water. Application of the biotechnology at the Kongdian bed (block no. 1) resulted in additional recovery of 6331 t oil. Oil viscosity in the zone of production wells located at the North block of the Kongdian bed decreased by 11%. A total of 46152 t additional oil was recovered at three experimental sites of the Dagang oilfield (North block and block no. 1 of the Kongdian bed and the Gangxi bed), which is an indication of high efficiency of the technology for activation of the oilfield microflora for heavy oil replacement from high-temperature oilfields.     

Microbiological and production characteristics of the high-temperature Kongdian petroleum reservoir revealed during field trial of biotechnology for the enhancement of oil recovery

Microbiological technology for the enhancement of oil recovery based on the activation of the stratal microflora was tested in the high-temperature horizons of the Kongdian bed (60°C) of the Dagang oil-field (China). This biotechnology consists in the pumping of a water-air mixture and nitrogen and phosphorus mineral salts into the oil stratum through injection wells in order to stimulate the activity of the stratal microflora which produce oil-releasing metabolites. Monitoring of the physicochemical, microbiological, and production characteristics of the trial site has revealed large changes in the ecosystem as a result of the application of biotechnology. The cell numbers of thermophilic hydrocarbon-oxidizing, fermentative, sulfate-reducing, and methanogenic microorganisms increased 10–10000-fold. The rates of methanogenesis and sulfate reduction increased in the near-bottom zone of the injection wells and of some production wells. The microbial oil transformation was accompanied by the accumulation of bicarbonate ions, volatile fatty acids, and biosurfactants in the formation waters, as well as of CH₄ and CO₂ both in the gas phase and in the oil. Microbial metabolites promoted the additional recovery of oil. As a result of the application of biotechnology, the water content in the production liquid from the trial site decreased, and the oil content increased. This allowed the recovery of more than 14000 tons of additional oil over 3.5 years.     

IFT proteins accumulate during cell division and localize to the cleavage furrow in Chlamydomonas

Intraflagellar transport (IFT) proteins are well established as conserved mediators of flagellum/cilium assembly and disassembly. However, data has begun to accumulate in support of IFT protein involvement in other processes elsewhere in the cell. Here, we used synchronous cultures of Chlamydomonas to investigate the temporal patterns of accumulation and localization of IFT proteins during the cell cycle. Their mRNAs showed periodic expression that peaked during S and M phase (S/M). Unlike most proteins that are synthesized continuously during G1 phase, IFT27 and IFT46 levels were found to increase only during S/M phase. During cell division, IFT27, IFT46, IFT72, and IFT139 re-localized from the flagella and basal bodies to the cleavage furrow. IFT27 was further shown to be associated with membrane vesicles in this region. This localization pattern suggests a role for IFT in cell division.     

Water status indicators of lemon trees in response to flooding and recovery

Potted 2-year-old lemon trees [Citrus limon (L.) Burm. fil, cv. Verna] grafted on sour orange (C. aurantium L.) rootstock were subjected to flooding for 3 d. Control plants were irrigated daily to field capacity. Continuously (sap flow, trunk diameter fluctuations) and discretely (predawn and midday leaf water potential, leaf conductance) measured plant-based water status indicators were compared. The sensitivity of the maximum daily trunk shrinkage signal intensity to flooding and its behaviour during the recovery period demonstrated that this indicator is more feasible than the others for use in automatic irrigation. The responses to flooding of continuously and discretely measured plant-based water status indicators were very similar to those observed in response to drought stress indicating that it necessary to use soil water measurement automatic sensors to detect the cause of the stress. The results underlined the robustness of the compensation heat-pulse technique for estimating instantaneous and daily transpiration rates on flooding stress and recovery.     

An investigation into some physical and biotic effects of flooding on reservoir mud previously subjected to a period of aerial exposure

A series of laboratory experiments were carried out in order to investigate the effects of selected physical and biotic processes on the substratum of a recently flooded gently sloping marginal zone of Plover Cove Reservoir, Hong Kong. The physical effects of disturbance of the sediments promoted the redistribution of organic matter, as shown by differences in the percentage of organic matter in the supernatant and residue resulting when reservoir mud was stirred. It is suggested that such a process would promote the transfer of allochthonous organic carbon from the marginal zone (the area of input of such material) to the rest of the water body. Substrate characteristics were also influenced by the activities of two species of benthic gastropod,Sinotaia quadrata andMelanoides tuberculata. These animals increased the rate of production of particles from soaked blocks of parent mud when compared with experimental treatments in the absence of snails. Additionally both species enhanced the production of aggregates from fine sediments with a particle size of less than 125 µm. The magnitudes of both processes were statistically significant. Laboratory observations showed thatM. tuberculata had a significantly faster rate of aggregate and fine particulate production thanS. quadrata and it is possible that the former species may have the capacity to modify the substrate characteristics of the newly flooded marginal zone of Plover Cove.Department of Zoology, The University of Hong Kong     

Design of an ex vivo culture system to investigate the effects of shear stress on cardiovascular tissue

Mechanical forces are known to affect the biomechanical properties of native and engineered cardiovascular tissue. In particular, shear stress that results from the relative motion of heart valve leaflets with respect to the blood flow is one important component of their mechanical environment in vivo. Although different types of bioreactors have been designed to subject cells to shear stress, devices to expose biological tissue are few. In an effort to address this issue, the aim of this study was to design an ex vivo tissue culture system to characterize the biological response of heart valve leaflets subjected to a well-defined steady or time-varying shear stress environment. The novel apparatus was designed based on a cone-and-plate viscometer. The device characteristics were defined to limit the secondary flow effects inherent to this particular geometry. The determination of the operating conditions producing the desired shear stress profile was streamlined using a computational fluid dynamic (CFD) model validated with laser Doppler velocimetry. The novel ex vivo tissue culture system was validated in terms of its capability to reproduce a desired cone rotation and to maintain sterile conditions. The CFD results demonstrated that a cone angle of 0.5 deg, a cone radius of 40 mm, and a gap of 0.2 mm between the cone apex and the plate could limit radial secondary flow effects. The novel cone-and-plate permits to expose nine tissue specimens to an identical shear stress waveform. The whole setup is capable of accommodating four cone-and-plate systems, thus concomitantly subjecting 36 tissue samples to desired shear stress condition. The innovative design enables the tissue specimens to be flush mounted in the plate in order to limit flow perturbations caused by the tissue thickness. The device is capable of producing shear stress rates of up to 650 dyn cm(-2) s(-1) (i.e., maximum shear stress rate experienced by the ventricular surface of an aortic valve leaflet) and was shown to maintain tissue under sterile conditions for 120 h. The novel ex vivo tissue culture system constitutes a valuable tool toward elucidating heart valve mechanobiology. Ultimately, this knowledge will permit the production of functional tissue engineered heart valves, and a better understanding of heart valve biology and disease progression.     

Contrasting effects of habitat reduction,conversion and alteration on neutral and non neutral biological communities

While habitat transformation driven by human activities is the main driver of current biodiversity changes, there is still no framework to explore and forecast the effects of different types of habitat changes on the richness and composition of biological communities. To tackle this issue, we modeled the dynamics of a regional meta‐community, composed either of ecologically equivalent species (neutral model) or of generalist and specialist species (specialization model), and explored the impact of the overall reduction, patch conversion or alteration of an original habitat into one or several other habitats of different total carrying capacity on the community metrics at equilibrium. Our simulations reveal strong interactions between the community model considered (neutral or specialization model) and the type of habitat change. Under neutrality, the impact of habitat changes on richness can be approached by a power law species–individual relationship (SIR), which may at constant density be simplified into the widely used power law species–area relationship (SAR), independent of the type of change. However, in the presence of generalist and specialist species, we found that 1) while habitat reduction in area also leads to approximately power law SIRs and SARs, 2) patch conversion and alteration have more complex effects on regional species richness, and 3) habitat alteration elicits the functional homogenization of communities, involving a decrease of their average level of specialization.     

A pilot study to investigate the alteration of gut microbial profile in Dip2a knockout mice

International Microbiology - Accumulating evidence has pointed out that the gut-brain axis plays important roles in the etiology of autism spectrum disorder (ASD). Gut dysbiosis was reported in...     

Use of microelectrodes to investigate the effects of 2-chlorophenol on microbial activities in biofilms

In order to assess the applicability of using microelectrodes as a tool for inhibition tests, temporal and spatial inhibitory effects of 2-chlorophenol (2-CP) on O(2) respiration and nitrification activities in municipal wastewater biofilms were investigated using microelectrodes for O(2) and NH(4)(+). The time-course microelectrode measurements demonstrated that 2-CP inhibited O(2) respiration and nitrification activities within 6-18 min. The microbial activities were inhibited only in the upper 400 microm of the biofilms by 2-CP, and the bacteria present in the deeper parts of the biofilms were still active, probably due to limited penetration of 2-CP. These results could reasonably explain the difference in inhibitory ratios of the O(2) respiration and nitrification activities in the biofilms. O(2) respiration activity was incompletely inhibited, which was attributed to the presence of O(2) respiration activities in the deeper parts of the biofilm. In contrast, nitrification activity was significantly inhibited because ammonia-oxidizing bacteria were present in the upper parts of the biofilm. These results indicate that the microelectrodes with a very quick response time and a high spatial resolution are useful tools to study temporal and spatial inhibitory effects of inhibitors on in situ microbial activities in biofilms.     

水淹干扰对水库水滨带植物群落稳定性与种间关系的影响

受城市化与人类活动等因素影响而退化的水滨带植被的恢复与重建是近年来生态环境的热点问题。植物群落的种间关系直接影响植被的演替与恢复。以南水北调中线一期工程通水前的丹江口水库原有水滨带植被为研究对象,对年均多于9个月（海拔142 m以下）、6-9个月（海拔142-147 m）、3-6个月（海拔147-151 m）和少于3个月（海拔151-157 m）的4种不同强度水淹干扰的水滨带植物群落的稳定性和种间关系进行分析,探讨不同水淹干扰强度对水库水滨带植物群落稳定性及种间关系的影响。采用M.Godron稳定性测定法对植物群落稳定性进行分析,通过方差比率（VR）、χ²检验、联结系数（AC）以及Spearman秩相关检验对不同水淹干扰强度下的植物群落优势种进行种间关联分析。结果表明：（1）水库水滨带植物群落稳定性从高到低依次为水淹时长3-6个月、水淹时长6-9个月、水淹时长少于3个月和水淹时长多于9个月。中度水淹干扰下的植物群落稳定性要好于重度和轻度水淹干扰的植物群落;（2）不同水淹干扰强度下水滨带植物群落总体性关联表现为显著正相关。随着水淹时间增加,群落中正联结种对占总对数的比例呈下降趋势,负联结种对比例呈增加趋势,正负联结比值降低,群落内种间联结强度逐渐降低,说明水淹干扰强度增加会导致水滨带植物群落种群间相互依存关系减弱或竞争关系加剧。在此基础上,探讨不同水淹干扰强度下物种的空间分布和生态习性,并提出针对不同水淹干扰强度的水滨带植被恢复的物种选择建议。     

Effect of exogenous inoculants on enhancing oil recovery and indigenous bacterial community dynamics in long-term field pilot of low permeability reservoir

Pseudomonas aeruginosa DN1 strain and Bacillus subtilis QHQ110 strain were chosen as rhamnolipid and lipopeptide producer respectively, to evaluate the efficiency of exogenous inoculants on enhancing oil recovery (EOR) and to explore the relationship between injected bacteria and indigenous bacterial community dynamics in long-term filed pilot of Hujianshan low permeability water-flooded reservoir for 26 months. Core-flooding tests showed that the oil displacement efficiency increased by 18.46% with addition of exogenous consortia. Bacterial community dynamics using quantitative PCR and high-throughput sequencing revealed that the exogenous inoculants survived and could live together with indigenous bacterial populations. They gradually became the dominant community after the initial activation, while their comparative advantage weakened continually after 3 months of the first injection. The bacterial populations did not exert an observable change in the process of the second injection of exogenous inoculants. On account of facilitating oil emulsification and accelerating bacterial growth with oil as the carbon source by the injection of exogenous consortia, γ-proteobacteria was finally the prominent bacterial community at class level varying from 25.55 to 32.67%, and the dominant bacterial populations were increased by 2–3 orders of magnitude during the whole processes. The content of organic acids and rhamnolipids in reservoir were promoted with the change of bacterial community diversity, respectively. Cumulative oil increments reached 26,190 barrels for 13 months after the first injection, and 55,947 barrels of oil had been accumulated in all of A20 wells block through two rounds of bacterial consortia injection. The performance of EOR has a cumulative improvement by the injection of exogenous inoculants without observable inhibitory effect on the indigenous bacterial populations, demonstrating the application potential in low permeability water-flooded reservoirs.