Geobacillus strains that have potential value in microbial enhanced oil recovery

Investigating the mechanism of interfacial tension reduction through the combination of low-salinity water and bacteria

In the enhanced oil recovery (EOR) process, interfacial tension (IFT) has become a crucial factor because of its impact on the recovery of residual oil. The use of surfactants and biosurfactants can reduce IFT and enhance oil recovery by decreasing it. Asphaltene in crude oil has the structural ability to act as a surface-active material. In microbial-enhanced oil recovery (MEOR), biosurfactant production, even in small amounts, is a significant mechanism that reduces IFT. This study aimed to investigate fluid/fluid interaction by combining low biosurfactant values and low-salinity water using NaCl, MgCl2, and CaCl2 salts at concentrations of 0, 1000, and 5000 ppm, along with Geobacillus stearothermophilus. By evaluating the IFT, this study investigated different percentages of 0, 1, and 5 wt.% of varying asphaltene with aqueous bulk containing low-salinity water and its combination with bacteria. The results indicated G. Stearothermophilus led to the formation of biosurfactants, resulting in a reduction in IFT for both acidic and basic asphaltene. Moreover, the interaction between asphaltene and G. Stearothermophilus with higher asphaltene percentages showed a decrease in IFT under both acidic and basic conditions. Additionally, the study found that the interaction between acidic asphaltene and G. stearothermophilus, in the presence of CaCl2, NaCl, and MgCl2 salts, resulted in a higher formation of biosurfactants and intrinsic surfactants at the interface of the two phases, in contrast to the interaction involving basic asphaltene. These findings emphasize the dependence of the interactions between asphaltene and G. Stearothermophilus, salt, and bacteria on the specific type and concentration of asphaltene.

The bioremediation of the typical persistent organic pollutants (POPs) by microalgae-bacteria consortia: A systematic review

With industrialisation and the rapidly growing agricultural demand, many organic compounds have been leaked into the environment, causing serious damage to the biosphere. Persistent organic pollutants (POPs) are a type of toxic chemicals that are resistant to degradation through normal chemical, biological or photolytic approaches. With their stable chemical structures, POPs can be accumulated in the environment, and transported through wind and water, causing global environmental issues. Many researches have been conducted to remediate POPs contamination using various kinds of biological methods, and significant results have been seen. Microalgae-bacteria consortium is a newly developed concept for biological technology in contamination treatment, with the synergetic effects between microalgae and bacteria, their potential for pollutants degradation can be further released. In this review, two types of POPs (polychlorinated biphenyls and polycyclic aromatic hydrocarbons) are selected as the targeted pollutants to give a systematic analysis of the biodegradation through microalgae and bacteria, including the species selection, the identification of dominant enzymes, as well as the real application performance of the consortia. In the end, some outlooks and suggestions are given to further guide the development of applying microalgae-bacteria consortia in remediating POPs contamination. In general, the coculturing of microalgae and bacteria is a novel and efficient way to fulfil the advanced treatment of POPs in soil or liquid phase, and both monooxygenase and dioxygenase belonging to oxygenase play a vital role in the biodegradation of PCBs and PAHs. This review provides a general guide in the future investigation of biological treatment of POPs.

Structural Diversity of the Lipopeptide Biosurfactant Produced by a Newly Isolated Strain, Geobacillus thermodenitrifcans ME63

The genus Geobacillus is active in degradation of hydrocarbons in thermophilic and facultative environments since it was first reported in 1920. Here, we report a new strain, Geobacillus thermodenitrificans ME63, isolated from an oilfield with the ability of producing the biosurfactant. The composition, chemical structure, and surface activity of the biosurfactant produced by G. thermodenitrificans ME63 were investigated by using a combination of the high-performance liquid chromatography, time-of-flight ion mass spectrometry, and surface tensiometer. The biosurfactant produced by strain ME63 was identified as surfactin with six variants, which is one of the representative family of lipopeptide biosurfactants. The amino acid residue sequence in the peptide of this surfactin is N-Glu → Leu → Leu → Val → Leu → Asp → Leu-C. The critical micelle concentration (CMC) of the surfactin is 55 mg L^-1, and the surface tension at CMC is 35.9 mN m^-1, which is promising in bioremediation and oil recovery industries. The surface activity and emulsification properties of biosurfactants produced by G. thermodenitrificans ME63 showed excellent resistance to temperature changes, salinity changes, and pH changes.

Medium-chain alkane biodegradation and its link to some unifying attributes of alkB genes diversity

Hydrocarbon footprints in the environment, via biosynthesis, natural seepage, anthropogenic activities and accidents, affect the ecosystem and induce a shift in the healthy biogeochemical equilibrium that drives needed ecological services. In addition, these imbalances cause human diseases and reduce animal and microorganism diversity. Microbial bioremediation, which capitalizes on functional genes, is a sustainable mitigation option for cleaning hydrocarbon-impacted environments. This review focuses on the bacterial alkB functional gene, which codes for a non-heme di‑iron monooxygenase (AlkB) with a di‑iron active site that catalyzes C₈-C₁₆ medium-chain alkane metabolism. These enzymes are ubiquitous and share common attributes such as being controlled by global transcriptional regulators, being a component of most super hydrocarbon degraders, and their distributions linked to horizontal gene transfer (HGT) events. The phylogenetic approach used in the HGT detection suggests that AlkB tree topology clusters bacteria functionally and that a preferential gradient dictates gene distribution. The alkB gene also acts as a biomarker for bioremediation, although it is found in pristine environments and absent in some hydrocarbon degraders. For instance, a quantitative molecular method has failed to link alkB copy number to contamination concentration levels. This limitation may be due to AlkB homologues, which have other functions besides n-alkane assimilation. Thus, this review, which focuses on Pseudomonas putida GPo1 alkB, shows that AlkB proteins are diverse but have some unifying trends around hydrocarbon-degrading bacteria; it is erroneous to rely on alkB detection alone as a monitoring parameter for hydrocarbon degradation, alkB gene distribution are preferentially distributed among bacteria, and the plausible explanation for AlkB affiliation to broad-spectrum metabolism of hydrocarbons in super-degraders hitherto reported. Overall, this review provides a broad perspective of the ecology of alkB-carrying bacteria and their directed biodegradation pathways.

Genetic and functional characterization of multiple thermophilic organosulfur-removal systems reveals desulfurization potentials for waste residue oil cleaning

Heavy oil and petroleum refining residues usually contain high concentrations of recalcitrant hazardous organosulfur compounds, causing long-term serious global environmental pollution during leakage and combustion. Research conducted here identified a unique thermophilic bacterium Parageobacillus thermoglucosidasius W-36 with the notable ability of waste residue oil desulfurization, utilization and tolerance of multiplex hazardous organosulfur pollutants. Genome information mining revealed multiple desulfurization systems in three organosulfur-utilizing gene clusters. Enzymatic characterization, phylogenetic relationships, transcriptional performance and structural prediction indicated four novel key monooxygenases for diverse organosulfur removal. Importantly, all monooxygenases shared obvious commonalities in the predicted tertiary structure backbone and catalytic characteristics of C-S bond cleavage, implying the potential of genetic engineering for broad-spectrum hazardous organosulfur removal. Therefore, this work demonstrated the important application potential of thermophilic bacteria as a promising alternative biodesulfurization way for waste residue oil cleaning.

Bacterial diversity and competitors for degradation of hazardous oil refining waste under selective pressures of temperature and oxygen

Oil refining waste (ORW) contains complex, hazardous, and refractory components, causing more severe long-term environmental pollution than petroleum. Here, ORW was used to simulate the accelerated domestication of bacteria from oily sludges and polymer-flooding wastewater, and the effects of key factors, oxygen and temperature, on the ORW degradation were evaluated. Bacterial communities acclimated respectively in 30/60 °C, aerobic/anaerobic conditions showed differentiated degradation rates of ORW, ranging from 5% to 34%. High-throughput amplicon sequencing and ORW component analysis revealed significant correlation between bacterial diversity/biomass and degradation efficiency/substrate preference. Under mesophilic and oxygen-rich condition, the high biomass and abundant biodiversity with diverse genes and pathways for petroleum hydrocarbons degradation, effectively promoted the rapid and multi-component degradation of ORW. While under harsh conditions, a few dominant genera still contributed to ORW degradation, although the biodiversity was severely restricted. The typical dominant facultative anaerobes Bacillus (up to 99.8% abundance anaerobically) and Geobacillus (up to 99.9% abundance aerobically and anaerobically) showed oxygen-independent sustainable degradation ability and broad-spectrum of temperature adaptability, making them promising and competitive bioremediation candidates for future application. Our findings provide important strategies for practical bioremediation of varied environments polluted by hazardous ORW.

Bacterial biofilm and extracellular polymeric substances in the moving bed biofilm reactor for wastewater treatment: A review

Among the several biofilm-based bioreactors, moving bed biofilm reactors (MBBR) have been extensively used for wastewater treatment due to low operational costs, technical feasibility, and stability. Biofilm forming strains, e.g., Stenotrophomonas maltophila DQ01, achieved 94.21% simultaneous nitrification and denitrification (SND) and 94.43% removal of total nitrogen (TN) at a cycle time of 7 h, and a biofilm consortium consisting of Chryseobacteriumsp. andRhodobactersp. achieved 86.8% removal of total organic carbon (TOC) at hydraulic retention time (HRT) of 24 h using lab-scale MBBR. Modifications in the surface properties of the biocarrier materials achieved 99.5 ± 1.1% chemical oxygen demand (COD) and 93.6 ± 2.3% NH₄⁺-N removal, significantly higher than the conventional commercial carrier. This review article summarizes the application of MBBR technology for wastewater treatment. The importance of bacterial biofilm and extracellular polymeric substances (EPS), anammox-n-DAMO coupled processes, and carrier surface modifications in MBBR technology have also been discussed.

Multi-parameter optimization maximizes the performance of genetically engineered Geobacillus for degradation of high-concentration nitroalkanes in wastewater

Nitroalkanes are important toxic pollutants for which there is no effective removal method at present. Although genetic engineering bacteria have been developed as a promising bioremediation strategy for years, their actual performance is far lower than expected. In this study, important factors affecting the application of engineered Geobacillus for nitroalkanes degradation were comprehensively optimized. The deep-reconstructed engineered strains significantly raised the expression and activity level of catalytic enzymes, but failed to fully enhance the degradation efficiency. However, further debugging of a variety of key parameters effectively improved the performance of the engineering strains. The increased cell membrane permeability, trace supplementation of vital nutritional factors, synergy of multifunctional enzyme engineered bacteria, switch of oxygen-supply mode, and moderate initial biomass all effectively boosted the degradation efficiency. Finally, a low-cost and highly effective bioreactor test for high-concentration nitroalkanes degradation proved the multi-parameter optimization mode helps to maximize the performance of genetically engineered bacteria.

Bioemulsification and Microbial Community Reconstruction in Thermally Processed Crude Oil

Utilization of low-cost, environmental-friendly microbial enhanced oil recovery (MEOR) techniques in thermal recovery-processed oil reservoirs is potentially feasible. However, how exogenous microbes facilitate crude oil recovery in this deep biosphere, especially under mesophilic conditions, is scarcely investigated. In this study, a thermal treatment and a thermal recurrence were processed on crude oil collected from Daqing Oilfield, and then a 30-day incubation of the pretreated crude oil at 37 °C was operated with the addition of two locally isolated hydrocarbon-degrading bacteria, Amycolicicoccus subflavus DQS3-9A1^T and Dietzia sp. DQ12-45-1b, respectively. The pH, surface tension, hydrocarbon profiles, culture-dependent cell densities and taxonomies, and whole and active microbial community compositions were determined. It was found that both A. subflavus DQS3-9A1^T and Dietzia sp. DQ12-45-1b successfully induced culture acidification, crude oil bioemulsification, and residual oil sub-fraction alteration, no matter whether the crude oil was thermally pretreated or not. Endogenous bacteria which could proliferate on double heated crude oil were very few. Compared with A. subflavus, Dietzia sp. was substantially more effective at inducing the proliferation of varied species in one-time heated crude oil. Meanwhile, the effects of Dietzia sp. on crude oil bioemulsification and hydrocarbon profile alteration were not significantly influenced by the ploidy increasing of NaCl contents (from 5 g/L to 50 g/L), but the reconstructed bacterial communities became very simple, in which the Dietzia genus was predominant. Our study provides useful information to understand MEOR trials on thermally processed oil reservoirs, and proves that this strategy could be operated by using the locally available hydrocarbon-degrading microbes in mesophilic conditions with different salinity degrees.

Genetically engineered thermotolerant facultative anaerobes for high-efficient degradation of multiple hazardous nitroalkanes

Nitroalkanes are important industrial raw materials but also toxic pollutants, which are difficult to degrade once released into the environment. In this study, to significantly improve the degradation-efficiency of multiple nitroalkanes, a facultative anaerobe was genetically engineered, possible influencing factors and simulated application experiments of bioreactor were tested and evaluated. Among all engineered recombinants, the most effective strains NG-S1 (anaerobic) and NG-S2 (aerobic) displayed 2-fold and 2.8-fold final degradation rates higher than the wild type, respectively. Exogenous components, particularly those that enhance coenzyme synthesis, helped to increase the degradation rate, as the level of coenzymes affected full function of overexpressed nitroalkane oxidase. Importantly, simulated mixed-nitroalkane-wastewater bioreactor experiments proved excellent and sustainable degradation performance of the engineered strains for potential industrial applications. Collectively, these findings provide a promising thermophilic biological engineering platform and a new perspective for high-efficient and continuous environmental bioremediation of hazardous pollutants under aerobic and anaerobic conditions.

Biodegradation of aliphatic and polycyclic aromatic hydrocarbons by the thermophilic bioemulsifier-producing Aeribacillus pallidus strain SL-1

The utilization of thermophilic hydrocarbon-degrading microorganisms is a suitable strategy for improving biodegradation of petroleum hydrocarbons and PAHs, as well as enhancing oil recovery from high-temperature reservoirs. In this study, the thermophilic strain Aeribacillus pallidus SL-1 was evaluated for the biodegradation of crude oil and PAHs at 60 °C. Strain SL-1 was found to preferentially degrade short-chain n-alkanes (<C17) and aromatic hydrocarbons from crude oil. The highest degradation rate of 84% was obtained with 1000 mg/l naphthalene as sole carbon source. Additionally, the strain was able to degrade 80% of phenanthrene (200 mg/l) and 50% of pyrene (50 mg/l) within 5 days at 60 °C. The SL-bioemulsifier produced by strain SL-1 was identified as a glycoprotein with stable emulsifying activity over a wide range of environmental conditions. Chemical composition studies exhibited that the SL-bioemulsifier consisted of polysaccharides (65.6%) and proteins (13.1%), among them, proteins were the major emulsifying functional substrates. Furthermore, the SL-bioemulsifier was able to enhance the solubility of PAHs. Thus, the bioemulsifier-producing strain SL-1 has great potential for applications in high-temperature bioremediation.