Population dynamics within a microbial consortium during growth on diesel fuel in saline environments

Microbial alchemists: unveiling the hidden potentials of halophilic organisms for soil restoration

Salinity, resulting from various contaminants, is a major concern to global crop cultivation. Soil salinity results in increased osmotic stress, oxidative stress, specific ion toxicity, nutrient deficiency in plants, groundwater contamination, and negative impacts on biogeochemical cycles. Leaching, the prevailing remediation method, is expensive, energy-intensive, demands more fresh water, and also causes nutrient loss which leads to infertile cropland and eutrophication of water bodies. Moreover, in soils co-contaminated with persistent organic pollutants, heavy metals, and textile dyes, leaching techniques may not be effective. It promotes the adoption of microbial remediation as an effective and eco-friendly method. Common microbes such as Pseudomonas, Trichoderma, and Bacillus often struggle to survive in high-saline conditions due to osmotic stress, ion imbalance, and protein denaturation. Halophiles, capable of withstanding high-saline conditions, exhibit a remarkable ability to utilize a broad spectrum of organic pollutants as carbon sources and restore the polluted environment. Furthermore, halophiles can enhance plant growth under stress conditions and produce vital bio-enzymes. Halophilic microorganisms can contribute to increasing soil microbial diversity, pollutant degradation, stabilizing soil structure, participating in nutrient dynamics, bio-geochemical cycles, enhancing soil fertility, and crop growth. This review provides an in-depth analysis of pollutant degradation, salt-tolerating mechanisms, and plant-soil-microbe interaction and offers a holistic perspective on their potential for soil restoration.

Different Responses of Bacteria and Archaea to Environmental Variables in Brines of the Mahai Potash Mine, Qinghai-Tibet Plateau

Salt mines feature both autochthonous and allochthonous microbial communities introduced by industrialization. It is important to generate the information on the diversity of the microbial communities present in the salt mines and how they are shaped by the environment representing ecological diversification. Brine from Mahai potash mine (Qianghai, China), an extreme hypersaline environment, is used to produce potash salts for hundreds of millions of people. However, halophiles preserved in this niche during deposition are still unknown. In this study, using high-throughput 16S rRNA gene amplicon sequencing and estimation of physicochemical variables, we examined brine samples collected from locations with the gradient of industrial activity intensity and discrete hydrochemical compositions in the Mahai potash mine. Our findings revealed a highly diverse bacterial community, mainly composed of Pseudomonadota in the hypersaline brines from the industrial area, whereas in the natural brine collected from the upstream Mahai salt lake, most of the 16S rRNA gene reads were assigned to Bacteroidota. Halobacteria and halophilic methanogens dominated archaeal populations. Furthermore, we discovered that in the Mahai potash mining area, bacterial communities tended to respond to anthropogenic influences. In contrast, archaeal diversity and compositions were primarily shaped by the chemical properties of the hypersaline brines. Conspicuously, distinct methanogenic communities were discovered in sets of samples with varying ionic compositions, indicating their strong sensitivity to the brine hydrochemical alterations. Our findings provide the first taxonomic snapshot of microbial communities from the Mahai potash mine and reveal the different responses of bacteria and archaea to environmental variations in this high-altitude aquatic ecosystem.

Bioelectrochemical degradation of petroleum hydrocarbons: A critical review and future perspectives

As typical pollutants, petroleum hydrocarbons that are widely present in various environmental media such as soil, water, sediments, and air, seriously endanger living organisms and human health. In the meantime, as a green environmental technology that integrates pollutant removal and resource recovery, bioelectrochemical systems (BESs) have been extensively applied to the removal of petroleum hydrocarbons from the environment. This review introduces working principles of BESs, following which it discusses the different reactor structures, application progresses, and key optimization factors when treating water, sewage sludges, sediments, and soil. Furthermore, bibliometrics was first used in this field to analyze the evolution of knowledge structure and forecast future hot topics. The research focus has shifted from the early generation of bioelectric energy to exploring mechanisms of soil remediation and microbial metabolisms, which will be closely integrated in the future. Finally, the future prospects of this field are proposed. This review focuses on the research status of bioelectrochemical degradation of petroleum hydrocarbons and provides a scientific reference for subsequent research.

Prospects in the bioremediation of petroleum hydrocarbon contaminants from hypersaline environments: A review

Hypersaline environments are underappreciated and are frequently exposed to pollution from petroleum hydrocarbons. Unlike other environs, the high salinity conditions present are a deterrent to various remediation techniques. There is also production of hypersaline waters from oil-polluted ecosystems which contain toxic hydrophobic pollutants that are threat to public health, environmental protection, and sustainability. Currently, innovative advances are being proposed for the remediation of oil-contaminated hypersaline regions. Such advancements include the exploration and stimulation of native microbial communities capable of utilizing and degrading petroleum hydrocarbons. However, prevailing salinity in these environments is unfavourable for the growth of non-halophylic microorganisms, thus limiting effective bioremediation options. An in-depth understanding of the potentials of various remediation technologies of hydrocarbon-polluted hypersaline environments is lacking. Thus, we present an overview of petroleum hydrocarbon pollution in hypersaline ecosystems and discuss the challenges and prospects associated with several technologies that may be employed in remediation of hydrocarbon pollution in the presence of delimiting high salinities. The application of biological remediation technologies including the utilization of halophilic and halotolerant microorganisms is also discussed.

Diversity of prokaryotic microorganisms in alkaline saline soil of the Qarhan Salt Lake area in the Qinghai-Tibet Plateau

The composition of microbial communities varies considerably across ecological environments, particularly in extreme environments, where unique microorganisms are typically used as the indicators of environmental conditions. However, the ecological reasons for the differences in microbial communities remain largely unknown. Herein, we analyzed taxonomic and functional community profiles via high-throughput sequencing to determine the alkaline saline soil bacterial and archaeal communities in the Qarhan Salt Lake area in the Qinghai-Tibet Plateau. The results showed that Betaproteobacteria (Proteobacteria) and Halobacteria (Euryarchaeota) were the most abundant in the soils of this area, which are common in high salinity environments. Accordingly, microbes that can adapt to local extremes typically have unique metabolic pathways and functions, such as chemoheterotrophy, aerobic chemoheterotrophy, nitrogen fixation, ureolysis, nitrate reduction, fermentation, dark hydrogen oxidation, and methanogenesis. Methanogenesis pathways include hydrogenotrophic methanogenesis, CO2 reduction with H2, and formate methanogenesis. Thus, prokaryotic microorganisms in high salinity environments are indispensable in nitrogen and carbon cycling via particular metabolic pathways.

A rapid change in microbial communities of the shale gas drilling fluid from 3548 m depth to the above-ground storage tank

Despite the growing body of studies on the various fracturing phrases, the research on the differences between subterranean and surface microorganisms at shale gas drilling sites is still limited. Generally, shale gas development and the production process are divided into drilling and fracturing. The distribution of microbial communities in the latter has been paid some attention, but a deficit remains in terms of our understanding of the microbial community in the former, especially for the phase of drilling flowback and drilling flowback surface. In this study, four drilling flowback fluids (DFFs) (H230-flowback drilling cuttings, H23G-flowback drilling mud, H240-flowback drilling sediment, and H21F-flowback drilling water) from the outlet of subterranean pipeline to the inlet of storage tank were successively collected from H2 shale gas field during its initial drilling in Sichuan, China. Natural mountain water (H10W) used as the injection water of H2 was also sampled. Illumina MiSeq 16S rRNA gene sequencing revealed a total of 8 phyla, 17 classes, 36 orders, 62 families, and 98 genera that were recovered from these samples with uneven distribution. The majority of the obtained sequences belonged to the phyla Proteobacteria (75.36%), Bacteroidetes (10.75%), and Firmicutes (5.64%), with significant differences found in DFFs and injection water. The richness of microorganisms gradually increased with the increasing flowback flowing distance (H230 < H23G < H240 < H21F < H10W), which was employed to reveal a rapid change in microbiota that was evident in samples along the flow path aboveground from a depth of 3548 m. The findings of this study could expand our understanding of the ecological role of microorganisms during the shale gas drilling phase. Furthermore, the study highlights the temporal-spatial trajectory of microbial communities from subterranean environments to the surface in a short period of 30 days.

Remediation of saline-sodic soil by plant microbial desalination cell

Saline-sodic soil is widely distributed around the world and has induced severe impacts on ecosystems and agriculture. Plant microbial desalination cell (PMDC) and soil microbial desalination cell (SMDC) were constructed to migrate excessive salt in the soil in this study. Compared with SMDC, PMDCs generated higher voltage ranging from 150 mV to 410 mV (500Ω) and the maximum power density reached 34 mW/m². Higher desalinization efficiency was obtained by PMDCs, the soil conductivity reduced from initial 2.4 mS/cm to 0.4 ± 0.1 mS/cm and pH decreased from initial 10.4 to 8.2 ± 0.1. Soils desalination in PMDCs was achieved through multiple pathways, including ion migration in PMDCs driven by electrokinetic process, plant absorption and bioremediation by plant roots and anode microorganism activity. Geobacter was the dominant electrogenic bacteria at the PMDC anode. The electrochemical and desalinating performance of PMDCs was enhanced by plants and provided a new method for remediation of saline-sodic soil.

Diversity and metagenome analysis of a hydrocarbon-degrading bacterial consortium from asphalt lakes located in Wietze, Germany

The pollution of terrestrial and aquatic environments by petroleum contaminants, especially diesel fuel, is a persistent environmental threat requiring cost-effective and environmentally sensitive remediation approaches. Bioremediation is one such approach, but is dependent on the availability of microorganisms with the necessary metabolic abilities and environmental adaptability. The aim of this study was to examine the microbial community in a petroleum contaminated site, and isolate organisms potentially able to degrade hydrocarbons. Through successive enrichment of soil microorganisms from samples of an historic petroleum contaminated site in Wietze, Germany, we isolated a bacterial consortium using diesel fuel hydrocarbons as sole carbon and energy source. The 16S rRNA gene analysis revealed the dominance of Alphaproteobacteria. We further reconstructed a total of 18 genomes from both the original soil sample and the isolated consortium. The analysis of both the metagenome of the consortium and the reconstructed metagenome-assembled genomes show that the most abundant bacterial genus in the consortium, Acidocella, possess many of the genes required for the degradation of diesel fuel aromatic hydrocarbons, which are often the most toxic component. This can explain why this genus proliferated in all the enrichment cultures. Therefore, this study reveals that the microbial consortium isolated in this study and its dominant genus, Acidocella, could potentially serve as an effective inoculum for the bioremediation of sites polluted with diesel fuel or other organic contaminants.

Exogenous application of signaling molecules to enhance the resistance of legume-rhizobium symbiosis in Pb/Cd-contaminated soils

Being signaling molecules, nitric oxide (NO) and hydrogen sulfide (H₂S) can mediate a wide range of physiological processes caused by plant metal toxicity. Moreover, legume-rhizobium symbiosis has gained increasing attention in mitigating heavy metal stress. However, systematic regulatory mechanisms used for the exogenous application of signaling molecules to alter the resistance of legume-rhizobium symbiosis under metal stress are currently unknown. In this study, we examined the exogenous effects of sodium nitroprusside (SNP) as an NO donor additive and sodium hydrosulfide (NaHS) as a H₂S donor additive on the phytotoxicity and soil quality of alfalfa (Medicago sativa)-rhizobium symbiosis in lead/cadmium (Pb/Cd)-contaminated soils. Results showed that rhizobia inoculation markedly promoted alfalfa growth by increasing chlorophyll content, fresh weight, and plant height and biomass. Compared to the inoculated rhizobia treatment alone, the addition of NO and H₂S significantly reduced the bioaccumulation of Pb and Cd in alfalfa-rhizobium symbiosis, respectively, thus avoiding the phytotoxicity caused by the excessive presence of metals. The addition of signaling molecules also alleviated metal-induced phytotoxicity by increasing antioxidant enzyme activity and inhibiting the level of lipid peroxidation and reactive oxygen species (ROS) in legume-rhizobium symbiosis. Also, signaling molecules improved soil nutrient cycling, increased soil enzyme activities, and promoted rhizosphere bacterial community diversity. Both partial least squares path modeling (PLS-PM) and variation partitioning analysis (VPA) identified that using signaling molecules can improve plant growth by regulating major controlling variables (i.e., soil enzymes, soil nutrients, and microbial diversity/plant oxidative damage) in legume-rhizobium symbiosis. This study offers integrated insight that confirms that the exogenous application of signaling molecules can enhance the resistance of legume-rhizobium symbiosis under metal toxicity by regulating the biochemical response of the plant-soil system, thereby minimizing potential health risks.

Co-inoculation effect of plant-growth-promoting rhizobacteria and rhizobium on EDDS assisted phytoremediation of Cu contaminated soils

Chelants application can increase the bioavailability of metals, subsequently limiting plant growth and reducing the efficiency of phytoremediation. Plant growth-promoting rhizobacteria (PGPRs) and rhizobium have substantial potential to improve plant growth and plant tolerance to metal stress. We evaluated the effects of co-inoculation with a PGPR strain (Paenibacillus mucilaginosus) and a Cu-resistant rhizobium strain (Sinorhizobium meliloti) on the efficiency of biodegradable chelant (S,S-ethylenediaminedisuccinic acid; EDDS) assisted phytoremediation of a Cu contaminated soil using alfalfa. The highest total Cu extraction by alfalfa was observed in the EDDS-treated soil upon co-inoculation with the PGPR and rhizobium strains, which was 1.2 times higher than that without co-inoculation. Partial least squares path modeling identified plant oxidative damage and soil microbial biomass as the key variables influencing Cu uptake by alfalfa roots. Co-inoculation significantly reduced the oxidative damage to alfalfa by mitigating the accumulation of malondialdehyde and reactive oxygen species, and improving the antioxidation capacity of the plant in the presence of EDDS. EDDS application decreased microbial diversity in the rhizosphere, whereas co-inoculation increased microbial biomass carbon and nitrogen, and microbial community diversity. Increased relative abundances of Actinobacteria and Bacillus and the presence of Firmicutes taxa as potential biomarkers demonstrated that co-inoculation increased soil nutrient content, and improved plant growth. Co-inoculation with PGPR and rhizobium can be useful for altering plant-soil biochemical responses during EDDS-enhanced phytoremediation to alleviate phytotoxicity of heavy metals and improve soil biochemical activities. This study provides an effective strategy for improving phytoremediation efficiency and soil quality during chelant assisted phytoremediation of metal-contaminated soils.

Sphingomonas: from diversity and genomics to functional role in environmental remediation and plant growth

The species belonging to the Sphingomonas genus possess multifaceted functions ranging from remediation of environmental contaminations to producing highly beneficial phytohormones, such as sphingan and gellan gum. Recent studies have shown an intriguing role of Sphingomonas species in the degradation of organometallic compounds. However, the actual biotechnological potential of this genus requires further assessment. Some of the species from the genus have also been noted to improve plant-growth during stress conditions such as drought, salinity, and heavy metals in agricultural soil. This role has been attributed to their potential to produce plant growth hormones e.g. gibberellins and indole acetic acid. However, the current literature is scattered, and some of the important areas, such as taxonomy, phylogenetics, genome mapping, and cellular transport systems, are still being overlooked in terms of elucidation of the mechanisms behind stress-tolerance and bioremediation. In this review, we elucidated the prospective role and function of this genus for improved utilization during environmental biotechnology.

Petroleum Hydrocarbon Contamination in Terrestrial Ecosystems-Fate and Microbial Responses

Petroleum hydrocarbons represent the most frequent environmental contaminant. The introduction of petroleum hydrocarbons into a pristine environment immediately changes the nature of that environment, resulting in reduced ecosystem functionality. Natural attenuation represents the single, most important biological process which removes petroleum hydrocarbons from the environment. It is a process where microorganisms present at the site degrade the organic contaminants without the input of external bioremediation enhancers (i.e., electron donors, electron acceptors, other microorganisms or nutrients). So successful is this natural attenuation process that in environmental biotechnology, bioremediation has developed steadily over the past 50 years based on this natural biodegradation process. Bioremediation is recognized as the most environmentally friendly remediation approach for the removal of petroleum hydrocarbons from an environment as it does not require intensive chemical, mechanical, and costly interventions. However, it is under-utilized as a commercial remediation strategy due to incomplete hydrocarbon catabolism and lengthy remediation times when compared with rival technologies. This review aims to describe the fate of petroleum hydrocarbons in the environment and discuss their interactions with abiotic and biotic components of the environment under both aerobic and anaerobic conditions. Furthermore, the mechanisms for dealing with petroleum hydrocarbon contamination in the environment will be examined. When petroleum hydrocarbons contaminate land, they start to interact with its surrounding, including physical (dispersion), physiochemical (evaporation, dissolution, sorption), chemical (photo-oxidation, auto-oxidation), and biological (plant and microbial catabolism of hydrocarbons) interactions. As microorganism (including bacteria and fungi) play an important role in the degradation of petroleum hydrocarbons, investigations into the microbial communities within contaminated soils is essential for any bioremediation project. This review highlights the fate of petroleum hydrocarbons in tertial environments, as well as the contributions of different microbial consortia for optimum petroleum hydrocarbon bioremediation potential. The impact of high-throughput metagenomic sequencing in determining the underlying degradation mechanisms is also discussed. This knowledge will aid the development of more efficient, cost-effective commercial bioremediation technologies.

Bacteria-assisted phytoremediation of fuel oil and lead co-contaminated soil in the salt-stressed condition by chromolaena odorata and Micrococcus luteus

Bioremediation of lead-petroleum co-contaminated soil under salt-stressed condition has been investigated. In this study, the co-contaminated soil (780 mg kg^-1 Pb and 27,000 mg kg^-1 TPHs) under the high salinity (EC 7.79 ds m^-1) was used as a model soil to be remediated by Chromolaena odorata inoculated with Micrococcus luteus. The results showed that salt stress caused a marked reduction in dry biomass and stem height, and high accumulation of proline. The presence of salt did not affect the total amount of chlorophyll in plant tissues. No toxicity symptoms were evident from plant morphology after three months of exposure. Drastic differences in the accumulation patterns of Pb in C. odorata grown on saline and non-saline soils were observed and indicated that salinity negatively affected Pb uptake and accumulation. A high rate of degradation of TPHs was observed in non-saline soils with or without bacterial inoculation. Salinity stress showed no significant different in the proportion of TPH degradation with added or non-added M. luteus. The tolerance of C. odorata and M. luteus to moderate concentrations of Pb and fuel oil made them very good candidates for the use in bacteria-assisted phytoremediation of lead-fuel oil co-contaminated soils under the mild saline soils.

Diesel uptake by an indigenous microbial consortium isolated from sediments of the Southern Gulf of Mexico: Emulsion characterisation

In this study a microbial consortium, dominated by members of the genera Marinobacter and Alcanivorax (Gammaproteobacteria) isolated from marine sediments of Southern Gulf of Mexico, was assessed to grow in a bubble column bioreactor using 13 g L^-1 of diesel (aliphatic and aromatic hydrocarbons mix including nonane and hexadecane) as the sole carbon source. The consortium was able to produce 3.3 g L^-1 of biomass, measured as suspended solids. Microbial growth was detectable, even substrate depletion, after 8 days of cultivation. The emulsifier activity and its influence on the droplet size were also evaluated: it was observed that droplet diameter decreases as emulsifier activity increases. The bubble column bioreactor system proposed in this research could be used as a biotechnological process for the remediation of a contaminated body in important petrochemical regions, for example, Veracruz, México, where some points of sea and fresh-water bodies were analysed to find nonane and hexadecane in all sample water. It is important due to a lack of information, regarding hydrocarbon pollution in this port area, is filled.

Diversity and Niche of Archaea in Bioremediation

Bioremediation is the use of microorganisms for the degradation or removal of contaminants. Most bioremediation research has focused on processes performed by the domain Bacteria; however, Archaea are known to play important roles in many situations. In extreme conditions, such as halophilic or acidophilic environments, Archaea are well suited for bioremediation. In other conditions, Archaea collaboratively work alongside Bacteria during biodegradation. In this review, the various roles that Archaea have in bioremediation is covered, including halophilic hydrocarbon degradation, acidophilic hydrocarbon degradation, hydrocarbon degradation in nonextreme environments such as soils and oceans, metal remediation, acid mine drainage, and dehalogenation. Research needs are addressed in these areas. Beyond bioremediation, these processes are important for wastewater treatment (particularly industrial wastewater treatment) and help in the understanding of the natural microbial ecology of several Archaea genera.

Hydrocarbon Degradation and Bacterial Community Responses During Remediation of Sediment Artificially Contaminated with Heavy Oil

　Natural biodegradation of heavy oil in the marine environment can be accelerated by the addition of nutrients or seeding of pre-selected microorganisms. In this study, a microcosm experiment was conducted to investigate the effects of inorganic nutrient supplementation (biostimulation) and bacterial consortium amendment (bioaugmentation) on the natural degradative processes of artificially contaminated sediment. Our results revealed that the addition of nutrients had greater effect on remediation than the addition of bacterial cells. Supplementation of inorganic nutrients promoted and sustained the growth of oil-degrading and heterotrophic bacteria throughout the experimental period. Highest reduction in the total petroleum hydrocarbons, and of their components, n-alkanes, polycylic aromatic hydrocarbons (PAHs) and alkyl PAHs, were obtained in the biostimulated microcosms. Changes in the bacterial community were monitored by the PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) method targeting the 16S rDNA gene. Results revealed different responses of the bacterial community to the addition of heavy oil and remediation agents. Shifts in the bacterial communities in the seawater were more dynamic than in the sediment. Results of this study showed that addition of remediation agents significantly enhanced the natural biodegradation of heavy oil in a sediment-seawater microcosm trial.

Biotechnological potential of microbial consortia and future perspectives

Design of a microbial consortium is a newly emerging field that enables researchers to extend the frontiers of biotechnology from a pure culture to mixed cultures. A microbial consortium enables microbes to use a broad range of carbon sources. It provides microbes with robustness in response to environmental stress factors. Microbes in a consortium can perform complex functions that are impossible for a single organism. With advancement of technology, it is now possible to understand microbial interaction mechanism and construct consortia. Microbial consortia can be classified in terms of their construction, modes of interaction, and functions. Here we discuss different trends in the study of microbial functions and interactions, including single-cell genomics (SCG), microfluidics, fluorescent imaging, and membrane separation. Community profile studies using polymerase chain-reaction denaturing gradient gel electrophoresis (PCR-DGGE), amplified ribosomal DNA restriction analysis (ARDRA), and terminal restriction fragment-length polymorphism (T-RFLP) are also reviewed. We also provide a few examples of their possible applications in areas of biopolymers, bioenergy, biochemicals, and bioremediation.

Bioremediation of oil-based drill cuttings by a halophilic consortium isolated from oil-contaminated saline soil

Oil-based drill cuttings are hazardous wastes containing complex hydrocarbons, heavy metals, and brine. Their remediation is a crucial step before release to the environment. In this work, we enriched a halophilic consortium, from oil-polluted saline soil, which is capable of degrading diesel as the main pollutant of oil-based drill cuttings. The degradation ability of the consortium was evaluated in microcosms using two different diluting agents (fine sand and biologically active soil). During the bioremediation process, the bacterial community dynamics of the microcosms was surveyed using PCR amplification of a fragment of 16S rRNA gene followed by denaturing gradient gel electrophoresis (DGGE). The diesel degradation rates were monitored by total petroleum hydrocarbon (TPH) measurement and the total count of heterotrophic and diesel-degrading bacteria. After 3 months, the microcosm containing fine sand and drill cuttings with the ratio of 1:1 (initial TPH of 36,000 mg/kg) showed the highest TPH removal (40%) and its dominant bacterial isolates belonged to the genera Dietzia, Arthrobacter, and Halomonas. DGGE results also confirmed the role of these genera in drill cuttings remediation. DGGE analysis of the bacterial diversity showed that Propionibacterium, Salinimicrobium, Marinobacter, and Dietzia are dominant in active soil microcosm; whereas Bacillus, Salinibacillus, and Marinobacter are abundant in sand microcosm. Our results suggest that the bioaugmentation strategy would be more successful if the diluting agent does not contain a complex microbial community.

Halophiles: biology, adaptation, and their role in decontamination of hypersaline environments

The unique cellular enzymatic machinery of halophilic microbes allows them to thrive in extreme saline environments. That these microorganisms can prosper in hypersaline environments has been correlated with the elevated acidic amino acid content in their proteins, which increase the negative protein surface potential. Because these microorganisms effectively use hydrocarbons as their sole carbon and energy sources, they may prove to be valuable bioremediation agents for the treatment of saline effluents and hypersaline waters contaminated with toxic compounds that are resistant to degradation. This review highlights the various strategies adopted by halophiles to compensate for their saline surroundings and includes descriptions of recent studies that have used these microorganisms for bioremediation of environments contaminated by petroleum hydrocarbons. The known halotolerant dehalogenase-producing microbes, their dehalogenation mechanisms, and how their proteins are stabilized is also reviewed. In view of their robustness in saline environments, efforts to document their full potential regarding remediation of contaminated hypersaline ecosystems merits further exploration.

Enhanced removal of petroleum hydrocarbons using a bioelectrochemical remediation system with pre-cultured anodes

Bioelectrochemical remediation (BER) systems such as microbial fuel cells (MFCs) have recently emerged as a green technology for the effective remediation of petroleum hydrocarbon contaminants (PH) coupled with simultaneous energy recovery. Recent research has shown that biofilms previously enriched for substrate degrading bacteria resulted in excellent performance in terms of substrate removal and electricity generation but the effects on hydrocarbon contaminant degradation were not examined. Here we investigate the differences between enriched biofilm anodes and freshly inoculated new anodes in diesel fed single chamber mediatorless microbial fuel cells (DMFC) using various techniques for the enhancement of PH contaminant remediation with concomitant electricity generation. An anodophilic microbial consortium previously selected for over a year through continuous culturing with a diesel concentration of about 800mgl(-1) and which now showed complete removal of this concentration of diesel within 30days was compared to that of a freshly inoculated new anode MFC (showing 83.4% removal of diesel) with a simultaneous power generation of 90.81mW/m(2) and 15.04mW/m(2) respectively. The behaviour of pre-cultured anodes at a higher concentration of PH (8000mgl(-1)) was also investigated. Scanning electron microscopy observation revealed a thick biofilm covering the pre-cultured anodic electrode but not the anode from the freshly inoculated MFC. High resolution imaging showed the presence of thin 60nm diametre pilus-like projections emanating from the cells. Anodic microbial community profiling confirmed that the selection for diesel degrading exoelectrogenic bacteria had occurred. Identification of a biodegradative gene (alkB) provided strong evidence of the catabolic pathway used for diesel degradation in the DMFCs.

Conversion of Uric Acid into Ammonium in Oil-Degrading Marine Microbial Communities: a Possible Role of Halomonads

Uric acid is a promising hydrophobic nitrogen source for biostimulation of microbial activities in oil-impacted marine environments. This study investigated metabolic processes and microbial community changes in a series of microcosms using sediment from the Mediterranean and the Red Sea amended with ammonium and uric acid. Respiration, emulsification, ammonium and protein concentration measurements suggested a rapid production of ammonium from uric acid accompanied by the development of microbial communities containing hydrocarbonoclastic bacteria after 3 weeks of incubation. About 80 % of uric acid was converted to ammonium within the first few days of the experiment. Microbial population dynamics were investigated by Ribosomal Intergenic Spacer Analysis and Illumina sequencing as well as by culture-based techniques. Resulting data indicated that strains related to Halomonas spp. converted uric acid into ammonium, which stimulated growth of microbial consortia dominated by Alcanivorax spp. and Pseudomonas spp. Several strains of Halomonas spp. were isolated on uric acid as the sole carbon source showed location specificity. These results point towards a possible role of halomonads in the conversion of uric acid to ammonium utilized by hydrocarbonoclastic bacteria.

Distribution of petroleum degrading genes and factor analysis of petroleum contaminated soil from the Dagang Oilfield, China

Genes that encode for enzymes that can degrade petroleum hydrocarbons (PHs) are critical for the ability of microorganisms to bioremediate soils contaminated with PHs. Distributions of two petroleum-degrading genes AlkB and Nah in soils collected from three zones of the Dagang Oilfield, Tianjin, China were investigated. Numbers of copies of AlkB ranged between 9.1 × 10(5) and 1.9 × 10(7) copies/g dry mass (dm) soil, and were positively correlated with total concentrations of PHs (TPH) (R(2) = 0.573, p = 0.032) and alkanes (C33 ~ C40) (R(2) = 0.914, p < 0.01). The Nah gene was distributed relatively evenly among sampling zones, ranging between 1.9 × 10(7) and 1.1 × 10(8) copies/g dm soil, and was negatively correlated with concentrations of total aromatic hydrocarbons (TAH) (R(2) = -0.567, p = 0.035) and ∑16 PAHs (R(2) = -0.599, p = 0.023). Results of a factor analysis showed that individual samples of soils were not ordinated as a function of the zones.

Complete genome sequence analysis of Pseudomonas aeruginosa N002 reveals its genetic adaptation for crude oil degradation

The present research work reports the whole genome sequence analysis of Pseudomonas aeruginosa strain N002 isolated from crude oil contaminated soil of Assam, India having high crude oil degradation ability. The whole genome of the strain N002 was sequenced by shotgun sequencing using Ion Torrent method and complete genome sequence analysis was done. It was found that the strain N002 revealed versatility for degradation, emulsification and metabolizing of crude oil. Analysis of cluster of orthologous group (COG) revealed that N002 has significantly higher gene abundance for cell motility, lipid transport and metabolism, intracellular trafficking, secretion and vesicular transport, secondary metabolite biosynthesis, transport and catabolism, signal transduction mechanism and transcription than average levels found in other genome sequences of the same bacterial species. However, lower gene abundance for carbohydrate transport and metabolism, replication, recombination and repair, translation, ribosomal structure, biogenesis was observed in N002 than average levels of other bacterial species.

Microbial community structure and diversity in an integrated system of anaerobic-aerobic reactors and a constructed wetland for the treatment of tannery wastewater in Modjo, Ethiopia

A culture-independent approach was used to elucidate the microbial diversity and structure in the anaerobic-aerobic reactors integrated with a constructed wetland for the treatment of tannery wastewater in Modjo town, Ethiopia. The system has been running with removal efficiencies ranging from 94%-96% for COD, 91%-100% for SO4(2-) and S(2-), 92%-94% for BOD, 56%-82% for total Nitrogen and 2%-90% for NH3-N. 16S rRNA gene clone libraries were constructed and microbial community assemblies were determined by analysis of a total of 801 unique clone sequences from all the sites. Operational Taxonomic Unit (OTU)--based analysis of the sequences revealed highly diverse communities in each of the reactors and the constructed wetland. A total of 32 phylotypes were identified with the dominant members affiliated to Clostridia (33%), Betaproteobacteria (10%), Bacteroidia (10%), Deltaproteobacteria (9%) and Gammaproteobacteria (6%). Sequences affiliated to the class Clostridia were the most abundant across all sites. The 801 sequences were assigned to 255 OTUs, of which 3 OTUs were shared among the clone libraries from all sites. The shared OTUs comprised 80 sequences belonging to Clostridiales Family XIII Incertae Sedis, Bacteroidetes and unclassified bacterial group. Significantly different communities were harbored by the anaerobic, aerobic and rhizosphere sites of the constructed wetland. Numerous representative genera of the dominant bacterial classes obtained from the different sample sites of the integrated system have been implicated in the removal of various carbon- containing pollutants of natural and synthetic origins. To our knowledge, this is the first report of microbial community structure in tannery wastewater treatment plant from Ethiopia.

Phylogenetic and functional diversity within toluene-degrading, sulphate-reducing consortia enriched from a contaminated aquifer

Three toluene-degrading microbial consortia were enriched under sulphate-reducing conditions from different zones of a benzene, toluene, ethylbenzene and xylenes (BTEX) plume of two connected contaminated aquifers. Two cultures were obtained from a weakly contaminated zone of the lower aquifer, while one culture originated from the highly contaminated upper aquifer. We hypothesised that the different habitat characteristics are reflected by distinct degrader populations. Degradation of toluene with concomitant production of sulphide was demonstrated in laboratory microcosms and the enrichment cultures were phylogenetically characterised. The benzylsuccinate synthase alpha-subunit (bssA) marker gene, encoding the enzyme initiating anaerobic toluene degradation, was targeted to characterise the catabolic diversity within the enrichment cultures. It was shown that the hydrogeochemical parameters in the different zones of the plume determined the microbial composition of the enrichment cultures. Both enrichment cultures from the weakly contaminated zone were of a very similar composition, dominated by Deltaproteobacteria with the Desulfobulbaceae (a Desulfopila-related phylotype) as key players. Two different bssA sequence types were found, which were both affiliated to genes from sulphate-reducing Deltaproteobacteria. In contrast, the enrichment culture from the highly contaminated zone was dominated by Clostridia with a Desulfosporosinus-related phylotype as presumed key player. A distinct bssA sequence type with high similarity to other recently detected sequences from clostridial toluene degraders was dominant in this culture. This work contributes to our understanding of the niche partitioning between degrader populations in distinct compartments of BTEX-contaminated aquifers.

Contrasting microbial functional genes in two distinct saline-alkali and slightly acidic oil-contaminated sites

To compare the functional gene structure and diversity of microbial communities in saline-alkali and slightly acidic oil-contaminated sites, 40 soil samples were collected from two typical oil exploration sites in North and South China and analyzed with a comprehensive functional gene array (GeoChip 3.0). The overall microbial pattern was significantly different between the two sites, and a more divergent pattern was observed in slightly acidic soils. Response ratio was calculated to compare the microbial functional genes involved in organic contaminant degradation and carbon, nitrogen, phosphorus, and sulfur cycling. The results indicated a significantly low abundance of most genes involved in organic contaminant degradation and in the cycling of nitrogen and phosphorus in saline-alkali soils. By contrast, most carbon degradation genes and all carbon fixation genes had similar abundance at both sites. Based on the relationship between the environmental variables and microbial functional structure, pH was the major factor influencing the microbial distribution pattern in the two sites. This study demonstrated that microbial functional diversity and heterogeneity in oil-contaminated environments can vary significantly in relation to local environmental conditions. The limitation of nitrogen and phosphorus and the low degradation capacity of organic contaminant should be carefully considered, particularly in most oil-exploration sites with saline-alkali soils.

Cytometric fingerprints: evaluation of new tools for analyzing microbial community dynamics

Optical characteristics of individual bacterial cells of natural communities can be measured with flow cytometry (FCM) in high throughput. The resulting data are visualized in cytometric histograms. These histograms represent individual cytometric fingerprints of microbial communities, e.g., at certain time points or microenvironmental conditions. Up to now four tools for analyzing the variation in these cytometric fingerprints are available but have not yet been systematically compared regarding application: Dalmatian Plot, Cytometric Histogram Image Comparison (CHIC), Cytometric Barcoding (CyBar), and FlowFP. In this article these tools were evaluated concerning (i) the required experience of the operator in handling cytometric data sets, (ii) the detection level of changes, (iii) time demand for analysis, and (iv) software requirements. As an illustrative example, FCM was used to characterize the microbial community structure of electroactive microbial biofilms. Their cytometric fingerprints were determined, analyzed with all four tools, and correlated to experimental and functional parameters. The source of inoculum (four different types of wastewater samples) showed the strongest influence on the microbial community structure and biofilm performance while the choice of substrate (acetate or lactate) had no significant effect in the present study. All four evaluation tools were found suitable to monitor structural changes of natural microbial communities. The Dalmatian Plot was shown to be most sensitive to operator impact but nevertheless provided an overview on community shifts. CHIC, CyBar, and FlowFP showed less operator dependence and gave highly resolved information on community structure variation on different detection levels. In conclusion, experimental and productivity parameters correlated with the biofilm structures and practical process integration details were available from cytometric fingerprint analysis.

Biodegradation of organic pollutants in saline wastewater by halophilic microorganisms: a review

Agro-food, petroleum, textile, and leather industries generate saline wastewater with a high content of organic pollutants such as aromatic hydrocarbons, phenols, nitroaromatics, and azo dyes. Halophilic microorganisms are of increasing interest in industrial waste treatment, due to their ability to degrade hazardous substances efficiently under high salt conditions. However, their full potential remains unexplored. The isolation and identification of halophilic and halotolerant microorganisms from geographically unrelated and geologically diverse hypersaline sites supports their application in bioremediation processes. Past investigations in this field have mainly focused on the elimination of polycyclic aromatic hydrocarbons and phenols, whereas few studies have investigated N-aromatic compounds, such as nitro-substituted compounds, amines, and azo dyes, in saline wastewater. Information regarding the growth conditions and degradation mechanisms of halophilic microorganisms is also limited. In this review, we discuss recent research on the removal of organic pollutants such as organic matter, in terms of chemical oxygen demand (COD), dyes, hydrocarbons, N-aliphatic and N-aromatic compounds, and phenols, in conditions of high salinity. In addition, some proposal pathways for the degradation of aromatic compounds are presented.

Bioremediation of oily hypersaline soil and water via potassium and magnesium amendment

Ten hydrocarbonoclastic halobacterial species and 5 haloarchaeal species that had been isolated on a mineral medium with oil as the sole carbon source grew better and consumed more crude oil, as measured by gas–liquid chromatography, in media receiving between 0.50 and 0.75 mol/L KCl and between 1.50 and 2.25 mol/L MgSO4. Chemical analysis revealed that within a certain limit, the higher the KCl and MgSO4 concentrations in the medium, the more K+ and Mg2+, respectively, was accumulated by cells of all the tested halobacteria and haloarchaea. Also, in experiments in which total natural microbial consortia in hypersaline soil and water samples were directly used as inocula, the consumption of hydrocarbons was enhanced in the presence of the above given concentrations of KCl and MgSO4. It was concluded that amendment with calculated concentrations of K+ and Mg2+ could be a promising practice for hydrocarbon bioremediation in hypersaline environments.

Bias problems in culture-independent analysis of environmental bacterial communities: a representative study on hydrocarbonoclastic bacteria

Culture-dependent methods for bacterial community analysis are currently considered obsolete; therefore, molecular techniques are usually used instead. The results of the current study on hydrocarbonoclastic bacteria in various oily habitats in Kuwait showed however, that the bacterial identities varied dramatically according to the analytical approach used. For six desert and six seawater samples used in this study, the culture-independent and culture-dependent techniques each led to a unique bacterial composition. Problems related to the culture-dependent technique are well known. The results of the current study highlighted bias problems other than those already recorded in the literature for the molecular approaches. Thus, for example, in contrast to the culture-dependent technique, the primers used in the molecular approach preferentially amplified the 16S rDNAs of hydrocarbonoclastic bacteria in total genomic DNAs of all the studied environmental samples, and in addition, failed to reveal in any environmental sample members of the Actinobacteria. The primers used in the molecular approach also amplified certain “pure” 16S rDNAs, but failed to do so when these DNAs were in mixture. In view of these results, it is recommended that the two analytical approaches should be used simultaneously because their combined results would reflect the bacterial community composition more precisely than either of them can do alone.

Bacteria associated with sabellids (Polychaeta: Annelida) as a novel source of surface active compounds

A total of 69 bacteria were isolated from crude oil enrichments of the polychaetes Megalomma claparedei, Sabella spallanzanii and Branchiomma luctuosum, and screened for biosurfactant (BS) production by conventional methods. Potential BS-producers (30 isolates) were primarily selected due to the production of both interesting spots on thin layer chromatography (TLC) plates and highly stable emulsions (E₂₄ ≥ 50%). Only few strains grew on cetyltrimethylammonium bromide and blood agar plates, indicating the probable production of anionic surfactants. The 16S rRNA gene sequencing revealed that selected isolates mainly belonged to the CFB group of Bacteroidetes, followed by Gammaproteobacteria and Alphaproteobacteria. A number of BS-producers belonged to genera (i.e., Cellulophaga, Cobetia, Cohaesibacter, Idiomarina, Pseudovibrio and Thalassospira) that have been never reported as able to produce BSs, even if they have been previously detected in hydrocarbon-enriched samples. Our results suggest that filter-feeding Polychaetes could represent a novel and yet unexplored source of biosurfactant-producing bacteria.

Microbial genetic diversity and ciliate community structure along an environmental gradient in coastal soil

We investigated the microbial genetic diversity and ciliate community in coastal soil from five sites with an environmental gradient using denaturing gradient gel electrophoresis (DGGE), gene sequencing and the Ludox-QPS method. The analyses of both the 16S ribosomal RNA (rRNA) gene and 18S rRNA gene DGGE resulted in equal or even a higher number of bands found in the samples taken from the high-salinity sites IV and V than in those taken from the low-to-moderate-salinity sites I-III. Cluster analysis of both DGGE profiles classified the five sites into three main groups (sites I, II and III and IV and V), which corresponded well to the analysis of environmental factors. There were 13 species observed at site I, three species at site II and nine species at site III, while no active ciliates were observed at the high-salinity sites IV and V. By contrast, the ciliate-specific DGGE revealed a higher number of bands in the samples taken from the high-salinity soil. Furthermore, gene sequencing suggested that the ciliates in the high-salinity soil comprised forms originating not only from soil but also from marine environments. The data indicate that saline soil may maintain a high diversity of ciliates and soil salinity might be the most influential factor regulating the community structure of ciliates.

Oil-bioremediation potential of two hydrocarbonoclastic, diazotrophic Marinobacter strains from hypersaline areas along the Arabian Gulf coasts

Two halophilic, hydrocarbonoclastics bacteria, Marinobacter sedimentarum and M. flavimaris, with diazotrophic potential occured in hypersaline waters and soils in southern and northern coasts of Kuwait. Their numbers were in the magnitude of 10(3) colony forming units g(-1). The ambient salinity in the hypersaline environments was between 3.2 and 3.5 M NaCl. The partial 16S rRNA gene sequences of the two strains showed, respectively, 99 and 100% similarities to the sequences in the GenBank. The two strains failed to grow in the absence of NaCl, exhibited best growth and hydrocarbon biodegradation in the presence of 1 to 1.5 M NaCl, and still grew and maintained their hydrocarbonoclastic activity at salinities up to 5 M NaCl. Both species utilized Tween 80, a wide range of individual aliphatic hydrocarbons (C9-C40) and the aromatics benzene, biphenyl, phenanthrene, anthracene and naphthalene as sole sources of carbon and energy. Experimental evidence was provided for their nitrogen-fixation potential. The two halophilic Marinobacter strains successfully mineralized crude oil in nutrient media as well as in hypersaline soil and water microcosms without the use of any nitrogen fertilizers.

Monitoring functions in managed microbial systems by cytometric bar coding

Cytometric monitoring of microbial community dynamics can be used to estimate stability of technical microbial processes like biogas production by analysis of segregated cell abundance changes. In this study, structure variations of a biogas community were cytometrically recorded over 9 months and found to be of diagnostic value for process details. The reactor regime was intentionally disturbed with regard to substrate overload or H(2)S accumulation. A single-cell based approach called cytometric bar coding (CyBar) for fast identification of reactive subcommunities was used. Functionality of specific subcommunities was uncovered by processing CyBar data with abiotic reactor parameters using Spearman's correlation coefficient. Twenty subcommunities showed a discrete and divergent behavior. For example, a 4-fold substrate overload increased the cell number of two acidogenic index subcommunities to 176 and 193% within three days. Supplementary analyses were done using DNA fingerprinting, cloning, and sequencing. Bioreactor perturbations were shown to create cell abundance changes in subcommunities rather than variations in their phylogenetic composition. The used workflow and macros are ready-to-use tools and allow on-site monitoring and interpretation of variation in microbial community functions within a few hours.

Microbial communities associated with wet flue gas desulfurization systems

Flue gas desulfurization (FGD) systems are employed to remove SO(x) gasses that are produced by the combustion of coal for electric power generation, and consequently limit acid rain associated with these activities. Wet FGDs represent a physicochemically extreme environment due to the high operating temperatures and total dissolved solids (TDS) of fluids in the interior of the FGD units. Despite the potential importance of microbial activities in the performance and operation of FGD systems, the microbial communities associated with them have not been evaluated. Microbial communities associated with distinct process points of FGD systems at several coal-fired electricity generation facilities were evaluated using culture-dependent and -independent approaches. Due to the high solute concentrations and temperatures in the FGD absorber units, culturable halothermophilic/tolerant bacteria were more abundant in samples collected from within the absorber units than in samples collected from the makeup waters that are used to replenish fluids inside the absorber units. Evaluation of bacterial 16S rRNA genes recovered from scale deposits on the walls of absorber units revealed that the microbial communities associated with these deposits are primarily composed of thermophilic bacterial lineages. These findings suggest that unique microbial communities develop in FGD systems in response to physicochemical characteristics of the different process points within the systems. The activities of the thermophilic microbial communities that develop within scale deposits could play a role in the corrosion of steel structures in FGD systems.

Natural attenuation of contaminated marine sediments from an old floating dock Part II: changes of sediment microbial community structure and its relationship with environmental variables

Changes of microbial community structure and its relationship with various environmental variables in surface marine sediments were examined for a one-year period after the removal of an old floating dock in Hong Kong SAR, South China. Temporal variations in the microbial community structure were clearly revealed by principal component analysis (PCA) of the microbial ester-linked fatty acid methyl ester (EL-FAME) profiles. The most obvious shift in microbial community structure was detected 6 months after the removal of the dock, although no significant decline in the levels of pollutants could be detected. As determined by EL-FAME profiles, the microbial diversity recovered and the predominance of gram-negative bacteria was gradually replaced by gram-positive bacteria and fungi in the impacted stations. With redundancy analysis (RDA), the concentration of total polycyclic aromatic hydrocarbons (PAHs) was found to be the second important determinant of microbial community structure, next to Time. The relative abundance of 18:1ω9c and hydroxyl fatty acids enriched in the PAH hot spots, whereas 16:1ω9 and 18:1ω9t were negatively correlated to total PAH concentration. The significant relationships observed between microbial EL-FAME profiles and pollutants, exampled by PAHs in the present study, suggested the potential of microbial community analysis in the assessment of the natural attenuation process in contaminated environments.

The genome sequence of Polymorphum gilvum SL003B-26A1(T) reveals its genetic basis for crude oil degradation and adaptation to the saline soil

Polymorphum gilvum SL003B-26A1^T is the type strain of a novel species in the recently published novel genus Polymorphum isolated from saline soil contaminated with crude oil. It is capable of using crude oil as the sole carbon and energy source and can adapt to saline soil at a temperature of 45°C. The Polymorphum gilvum genome provides a genetic basis for understanding how the strain could degrade crude oil and adapt to a saline environment. Genome analysis revealed the versatility of the strain for emulsifying crude oil, metabolizing aromatic compounds (a characteristic specific to the Polymorphum gilvum genome in comparison with other known genomes of oil-degrading bacteria), as well as possibly metabolizing n-alkanes through the LadA pathway. In addition, COG analysis revealed Polymorphum gilvum SL003B-26A1^T has significantly higher abundances of the proteins responsible for cell motility, lipid transport and metabolism, and secondary metabolite biosynthesis, transport and catabolism than the average levels found in all other genomes sequenced thus far, but lower abundances of the proteins responsible for carbohydrate transport and metabolism, defense mechanisms, and translation than the average levels. These traits support the adaptability of Polymorphum gilvum to a crude oil-contaminated saline environment. The Polymorphum gilvum genome could serve as a platform for further study of oil-degrading microorganisms for bioremediation and microbial-enhanced oil recovery in harsh saline environments.

Correlation of community dynamics and process parameters as a tool for the prediction of the stability of wastewater treatment

Wastewater treatment often suffers from instabilities and the failure of specific functions such as biological phosphorus removal by polyphosphate accumulating organisms. Since most of the microorganisms involved in water clarification are unknown it is challenging to operate the process accounting for the permanent varying abiotic parameters and the complex composition and unrevealed metabolic capacity of a wastewater microbial community. Fulfilling the demands for water quality irrespective of substrate inflow conditions may emit severe problems if the limited management resources of municipal wastewater treatment plants are regarded. We used flow cytometric analyses of cellular DNA and polyphosphate to create patterns mirroring dynamics in community structure. These patterns were resolved in up to 15 subclusters, the presence and abundances of which correlated with abiotic data. The study used biostatistics to determine the kind and strength of the correlation. Samples investigated were obtained from a primary clarifier and two activated sludge basins. The stability of microbial community structure was found to be high in the basins and low in the primary clarifier. Despite major abiotic changes certain subcommunities were dominantly present (up to 80% stability), whereas others emerged only sporadically (down to 3% stability, both according to equivalence testing). Additionally, subcommunities of diagnostic value were detected showing positive correlation with substrate influxes. For instance blackwater (r(s) = 0.5) and brewery inflow (both r(s) = 0.6) were mirrored by increases in cell abundances in subclusters 1 and 6 as well as 4 and 8, respectively. Phosphate accumulation was obviously positively correlated with nitrate (r(s) = 0.4) and the presence of denitrifying organisms (Rhodacyclaceae). Various other correlations between community structure and abiotic parameters were apparent. The bacterial composition of certain subcommunities was determined by cell sorting and phylogenetic tools like T-RFLP. In essence, we developed a monitoring tool which is quick, cheap and causal in its interpretation. It will make laborious PCR based technique less obligatory as it allows reliable process monitoring and control in wastewater treatment plants.

Biodegradation of aromatic hydrocarbons by Haloarchaea and their use for the reduction of the chemical oxygen demand of hypersaline petroleum produced water

Ten halophilic Archaea (Haloarchaea) strains able to degrade aromatic compounds were isolated from five hypersaline locations; salt marshes in the Uyuni salt flats in Bolivia, crystallizer ponds in Chile and Cabo Rojo (Puerto Rico), and sabkhas (salt flats) in the Persian Gulf (Saudi Arabia) and the Dead Sea (Israel and Jordan). Phylogenetic identification of the isolates was determined by 16S rRNA gene sequence analysis. The isolated Haloarchaea strains were able to grow on a mixture of benzoic acid, p-hydroxybenzoic acid, and salicylic acid (1.5mM each) and a mixture of the polycyclic aromatic hydrocarbons, naphthalene, anthracene, phenanthrene, pyrene and benzo[a]anthracene (0.3mM each). Evaluation of the extent of degradation of the mixed aromatic hydrocarbons demonstrated that the isolates could degrade these compounds in hypersaline media containing 20% NaCl. The strains were shown to reduce the COD of hypersaline crude oil reservoir produced waters significantly beyond that achieved using standard hydrogen peroxide treatment alone.

Alkane-degrading properties of Dietzia sp. H0B, a key player in the Prestige oil spill biodegradation (NW Spain)

AIMS

Investigation of the alkane-degrading properties of Dietzia sp. H0B, one of the isolated Corynebacterineae strains that became dominant after the Prestige oil spill.

METHODS AND RESULTS

Using molecular and chemical analyses, the alkane-degrading properties of strain Dietzia sp. H0B were analysed. This Grampositive isolate was able to grow on n-alkanes ranging from C₁₂ to C₃₈ and branched alkanes (pristane and phytane). 8-Hexadecene was detected as an intermediate of hexadecane degradation by Dietzia H0B, suggesting a novel alkane-degrading pathway in this strain. Three putative alkane hydroxylase genes (one alkB homologue and two CYP153 gene homologues of cytochrome P450 family) were PCR-amplified from Dietzia H0B and differed from previously known hydroxylase genes, which might be related to the novel degrading activity observed on Dietzia H0B. The alkane degradation activity and the alkB and CYP153 gene expression were observed constitutively regardless of the presence of the substrate, suggesting additional, novel pathways for alkane degradation.

CONCLUSIONS

The results from this study suggest novel alkane-degrading pathways in Dietzia H0B and a genetic background coding for two different putative oil-degrading enzymes, which is mostly unexplored and worth to be subject of further functional analysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study increases the scarce information available about the genetic background of alkane degradation in genus Dietzia and suggests new pathways and novel expression mechanisms of alkane degradation.

Biological treatment of refinery spent caustics under halo-alkaline conditions

The present research demonstrates the biological treatment of refinery sulfidic spent caustics in a continuously fed system under halo-alkaline conditions (i.e. pH 9.5; Na(+)= 0.8M). Experiments were performed in identical gas-lift bioreactors operated under aerobic conditions (80-90% saturation) at 35°C. Sulfide loading rates up to 27 mmol L(-1)day(-1) were successfully applied at a HRT of 3.5 days. Sulfide was completely converted into sulfate by the haloalkaliphilic sulfide-oxidizing bacteria belonging to the genus Thioalkalivibrio. Influent benzene concentrations ranged from 100 to 600 μM. At steady state, benzene was removed by 93% due to high stripping efficiencies and biodegradation. Microbial community analysis revealed the presence of haloalkaliphilic heterotrophic bacteria belonging to the genera Marinobacter, Halomonas and Idiomarina which might have been involved in the observed benzene removal. The work shows the potential of halo-alkaliphilic bacteria in mitigating environmental problems caused by alkaline waste.