Biodegradation of benzene homologues in contaminated sediment of the East China Sea

Zunongwangia pacifica sp. nov., isolated from surface seawater of the Western Pacific Ocean

Zunongwangia is a group of marine bacteria with important industrial application potential and ecological functions. In this study, a Gram-stain-negative, rod-shaped, non-motile, strictly aerobic and bright yellow pigmented bacterial strain within this genus, designated C2-37M9^T, was isolated from a surface seawater sample from the Philippine Basin in the Western Pacific Ocean. Strain C2-37M9^T grew at 10-44 °C (optimum, 28-30 °C), pH 6-9 (pH 7) and in the presence of 0-12 % NaCl (w/v; 2-3 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that it belonged to the genus Zunongwangia and had 95.7-98.7 % sequence similarity to all type strains of this genus, with the highest value corresponding to Zunongwangia profunda (98.7 %). Digital DNA-DNA hybridization, average nucleotide identity and average amino acid identity values between strain C2-37M9^T and all valid type strains were 27.5-32.3, 83.8-86.7 and 86.9-89.0 %, respectively. The principal fatty acids (>5 %) were iso-C_15 : 0, iso-C_17 : 0 3-OH, anteiso-C_15 : 0, summed feature 9 (C_16 : 0 10-methyl and/or iso-C_17 : 1  ω9c), iso-C_15 : 1 G and summed feature 3 (C_16 : 1  ω6c and/or C_16 : 1  ω7c). The predominant respiratory quinone was MK-6. The polar lipids were one phosphatidylethanolamine, two unknown glycolipids, three unidentified aminolipids and six unidentified lipids. The genomic DNA G+C content of strain C2-37M9^T was 36.7 mol%. Based on phylogenetic results and genomic-based relatedness indices, as well as phenotypic and genotypic characteristics, strain C2-37M9^T represents a novel species within the genus Zunongwangia, for which the name Zunongwangia pacifica sp. nov. is proposed. The type strain is C2-37M9^T (=MCCC M21534^T=KCTC 82852^T).

Versatile mechanisms and enhanced strategies of pollutants removal mediated by Shewanella oneidensis: A review

The removal of environmental pollutants is important for a sustainable ecosystem and human health. Shewanella oneidensis (S. oneidensis) has diverse electron transfer pathways and can use a variety of contaminants as electron acceptors or electron donors. This paper reviews S. oneidensis's function in removing environmental pollutants, including heavy metals, inorganic non-metallic ions (INMIs), and toxic organic pollutants. S. oneidensis can mineralize o-xylene (OX), phenanthrene (PHE), and pyridine (Py) as electron donors, and also reduce azo dyes, nitro aromatic compounds (NACs), heavy metals, and iodate by extracellular electron transfer (EET). For azo dyes, NACs, Cr(VI), nitrite, nitrate, thiosulfate, and sulfite that can cross the membrane, S. oneidensis transfers electrons to intracellular reductases to catalyze their reduction. However, most organic pollutants cannot be directly degraded by S. oneidensis, but S. oneidensis can remove these pollutants by self-synthesizing catalysts or photocatalysts, constructing bio-photocatalytic systems, driving Fenton reactions, forming microbial consortia, and genetic engineering. However, the industrial-scale application of S. oneidensis is insufficient. Future research on the metabolism of S. oneidensis and interfacial reactions with other materials needs to be deepened, and large-scale reactors should be developed that can be used for practical engineering applications.

Response of chlorinated hydrocarbon transformation and microbial community structure in an aquifer to joint H2 and O2

Hydrogen (H2) and oxygen (O2) are critical electron donors and acceptors to promote the anaerobic and aerobic microbial transformation of chlorinated hydrocarbons (CHCs), respectively. Electrochemical technology can effectively supply H2 and O2 directly to an aquifer. However, the response of CHC transformation and microbial community structure to joint H2 and O2 are still unclear. In this work, microcosms containing different combinations of H2 and O2 were constructed with natural sediments and nine mixed CHCs. The joint H2 and O2 microcosm (H2/O2 microcosm) significantly promoted the biotransformation of trichloroethylene (TCE), trans-dichloroethene (tDCE) and chloroform (CF). Illumina sequencing analyses suggested that a particular microbial community was formed in the H2/O2 microcosm. The specific microbial species included Methyloversatilis, Dechloromonas, Sediminibacterium, Pseudomonas, Acinetobacter, Curvibacter, Comamonas and Acidovorax, and the relative abundance of the tceA, phe and soxB genes synchronously increased. These results suggested that some specific microbes are potential CHC converters using H2 and O2 as energy sources, and aerobic and anaerobic transformations exist simultaneously in the H2/O2 microcosm. It provides a theoretical basis for establishing efficient green remediation technologies for CHC contaminated aquifers.

Effects of Salinity on the Biodegradation of Polycyclic Aromatic Hydrocarbons in Oilfield Soils Emphasizing Degradation Genes and Soil Enzymes

The biodegradation of organic pollutants is the main pathway for the natural dissipation and anthropogenic remediation of polycyclic aromatic hydrocarbons (PAHs) in the environment. However, in the saline soils, the PAH biodegradation could be influenced by soil salts through altering the structures of microbial communities and physiological metabolism of degradation bacteria. In the worldwide, soils from oilfields are commonly threated by both soil salinity and PAH contamination, while the influence mechanism of soil salinity on PAH biodegradation were still unclear, especially the shifts of degradation genes and soil enzyme activities. In order to explain the responses of soils and bacterial communities, analysis was conducted including soil properties, structures of bacterial community, PAH degradation genes and soil enzyme activities during a biodegradation process of PAHs in oilfield soils. The results showed that, though low soil salinity (1% NaCl, w/w) could slightly increase PAH degradation rate, the biodegradation in high salt condition (3% NaCl, w/w) were restrained significantly. The higher the soil salinity, the lower the bacterial community diversity, copy number of degradation gene and soil enzyme activity, which could be the reason for reductions of degradation rates in saline soils. Analysis of bacterial community structure showed that, the additions of NaCl increase the abundance of salt-tolerant and halophilic genera, especially in high salt treatments where the halophilic genera dominant, such as Acinetobacter and Halomonas. Picrust2 and redundancy analysis (RDA) both revealed suppression of PAH degradation genes by soil salts, which meant the decrease of degradation microbes and should be the primary cause of reduction of PAH removal. The soil enzyme activities could be indicators for microorganisms when they are facing adverse environmental conditions.

Optimization of microbial fuel cell process using a novel consortium for aromatic hydrocarbon bioremediation and bioelectricity generation

Microbial Fuel Cell (MFC) is an innovative bio-electrochemical approach which converts biochemical energy inherent in wastewater into electrical energy, thus contributing to circular economy. Five electrogenic bacteria, Kocuria rosea (GTPAS76), two strains of Bacillus circulans (GTPO28 and GTPAS54), and two strains of Corynebacterium vitaeruminis (GTPO38 and GTPO42) were isolated from a common effluent treatment plant (CETP) and were used individually as well as in consortium form to run double chambered "H" type microbial fuel cell. Individually they could produce voltage in the range of 0.4-0.7 V in the MFC systems. Consortium developed using GTPO28, GTPO38, GTPAS54 and GTPAS76 were capable of producing voltage output of 0.8 V with 81.81 % and 64 % COD and BOD reduction, respectively. The EPS production capacity and electricity generation by the isolated bacteria correlated significantly (r = 0.72). Various parameters like, effect of preformed biofilm, length of salt bridge and its reuse, aeration, substrate concentration and external resistance were studied in detail. The study emphasizes on improving the commercialization aspect of MFC with repeated use of salt bridge and improving wastewater treatment potential after optimization of MFC system. Polarization curve and power density trends were studied in optimized MFC. A maximum power density and current density achieved were 18.15 mW/m² and 370.37 mA/m², respectively using 5 mM sodium benzoate. This study reports the use of sodium benzoate as a substrate along with reusing of the salt bridge in MFC study with promising results for BOD and COD reduction, proving it to be futuristic technology for bio-based circular ecosystem development.

Bacterial Composition Associated With Giant Colonies of the Harmful Algal Species Phaeocystis globosa

The cosmopolitan algae Phaeocystis globosa forms harmful algal blooms frequently in a number of tropical and subtropical coastal regions in the past two decades. During the bloom, the giant colony, which is formed by P. globosa, is the dominant morphotype. However, the microenvironment and the microbial composition in the intracolonial fluid are poorly understood. Here, we used high-throughput 16S rRNA amplicon sequencing to examine the bacterial composition and predicted functions in intracolonial fluid. Compared with the bacterial consortia in ambient seawater, intracolonial fluids possessed the lower levels of microbial richness and diversity, implying selectivity of bacteria by the unique intracolonial microenvironment enclosed within the P. globosa polysaccharide envelope. The bacterial consortia in intracolonial fluid were dominated by Balneola (48.6% of total abundance) and Labrezia (28.5%). The bacteria and microbial function enriched in intracolonial fluid were involved in aromatic benzenoid compounds degradation, DMSP and DMS production and consumption, and antibacterial compounds synthesis. We suggest that the P. globosa colonial envelope allows for the formation of a specific microenvironment; thus, the unique microbial consortia inhabiting intracolonial fluid has close interaction with P. globosa cells, which may benefit colony development.

Microbial Diversity and Activity During the Biodegradation in Seawater of Various Substitutes to Conventional Plastic Cotton Swab Sticks

The European Parliament recently approved a new law banning single-use plastic items for 2021 such as plastic plates, cutlery, straws, cotton swabs, and balloon sticks. Transition to a bioeconomy involves the substitution of these banned products with biodegradable materials. Several materials such as polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), poly(butylene succinate) (PBS), polyhydroxybutyrate-valerate (PHBV), Bioplast, and Mater-Bi could be good candidates to substitute cotton swabs, but their biodegradability needs to be tested under marine conditions. In this study, we described the microbial life growing on these materials, and we evaluated their biodegradability in seawater, compared with controls made of non-biodegradable polypropylene (PP) or biodegradable cellulose. During the first 40 days in seawater, we detected clear changes in bacterial diversity (Illumina sequencing of 16S rRNA gene) and heterotrophic activity (incorporation of ³H-leucine) that coincided with the classic succession of initial colonization, growth, and maturation phases of a biofilm. Biodegradability of the cotton swab sticks was then tested during another 94 days under strict diet conditions with the different plastics as sole carbon source. The drastic decrease of the bacterial activity on PP, PLA, and PBS suggested no bacterial attack of these materials, whereas the bacterial activity in PBAT, Bioplast, Mater-Bi, and PHBV presented similar responses to the cellulose positive control. Interestingly, the different bacterial diversity trends observed for biodegradable vs. non-biodegradable plastics allowed to describe potential new candidates involved in the degradation of these materials under marine conditions. This better understanding of the bacterial diversity and activity dynamics during the colonization and biodegradation processes contributes to an expanding baseline to understand plastic biodegradation in marine conditions and provide a foundation for further decisions on the replacement of the banned single-used plastics.

Effects of the insecticide fipronil in freshwater model organisms and microbial and periphyton communities

Fipronil is a broad-spectrum insecticide whose release in the environment damages many non-target organisms. This study evaluated the toxicity of fipronil at two biological levels using in vivo conditions and environmentally relevant concentrations: the first based on two model organisms (aquatic invertebrate Daphnia magna and the unicellular freshwater alga Chlamydomonas reinhardtii) and a second based on three natural communities (river periphyton and freshwater and soil microbial communities). The physicochemical properties of fipronil make it apparently unstable in the environment, so its behaviour was followed with high performance liquid chromatography (HPLC) under the different test conditions. The most sensitive organism to fipronil was D. magna, with median lethal dose (LC₅₀) values from 0.07 to 0.38 mg/L (immobilisation test). Toxicity was not affected by the media used (MOPS or river water), but it increased with temperature. Fipronil produced effects on the photosynthetic activity of C. reinhardtii at 20 °C in MOPS (EC₅₀ = 2.44 mg/L). The freshwater periphyton presented higher sensitivity to fipronil (photosynthetic yield EC₅₀ of 0.74 mg/L) in MOPS and there was a time-dependent effect (toxicity increased with time). Toxicity was less evident when periphyton and C. reinhardtii tests were performed in river water, where the solubility of fipronil is poor. Finally, the assessment of the metabolic profiles using Biolog EcoPlates showed that bacteria communities were minimally affected by fipronil. The genetic identification of these communities based on 16S rRNA gene sequencing revealed that many of the taxa are specialists in degrading high molecular weight compounds, including pesticides. This work allows us to better understand the impact of fipronil on the environment at different levels of the food chain and in different environmental conditions, a necessary point given its presence in the environment and the complex behaviour of this compound.

Characterization of sediment microbial communities at two sites with low hydrocarbon pollution in the southeast Gulf of Mexico

Background

Coastal ecosystems are prone to hydrocarbon pollution due to human activities, and this issue has a tremendous impact on the environment, socioeconomic consequences, and represents a hazard to humans. Bioremediation relies on the ability of bacteria to metabolize hydrocarbons with the aim of cleaning up polluted sites.

Methods

The potential of naturally occurring microbial communities as oil degraders was investigated in Sisal and Progreso, two port locations in the southeast Gulf of Mexico, both with a low level of hydrocarbon pollution. To do so, we determined the diversity and composition of bacterial communities in the marine sediment during the dry and rainy seasons using 16S rRNA sequencing. Functional profile analysis (PICRUTSt2) was used to predict metabolic functions associated with hydrocarbon degradation.

Results

We found a large bacterial taxonomic diversity, including some genera reported as hydrocarbon-degraders. Analyses of the alpha and beta diversity did not detect significant differences between sites or seasons, suggesting that location, season, and the contamination level detected here do not represent determining factors in the structure of the microbial communities. PICRUTSt2 predicted 10 metabolic functions associated with hydrocarbon degradation. Most bacterial genera with potential hydrocarbon bioremediation activity were generalists likely capable of degrading different hydrocarbon compounds. The bacterial composition and diversity reported here represent an initial attempt to characterize sites with low levels of contamination. This information is crucial for understanding the impact of eventual rises in hydrocarbon pollution.

Co-enhanced activated sludge system by static magnetic field and two halotolerant yeasts for azo dye treatment

The effect of static magnetic field (SMF) on azo dye Acid Red B (ARB) decolorization by the co-culture of activated sludge (AS) and two halotolerant yeasts Candida tropicalis A1 and Pichia occidentalis A2 was investigated. Microbial community structure of the co-cultures before and after treatment with SMFs of different intensity was analyzed through high-throughput sequencing and quantitative real-time polymerase chain reaction. The results showed that ARB decolorization efficiency by the defined co-culture was 1.25-fold to 1.51-fold elevated by 24.6-305.0 mT SMF. The best ARB decolorization and chemical oxygen demand (COD) removal performances by the co-culture were both achieved with 95.0 mT SMF. By contrast, biomass multiplication and sedimentation property of AS systems were not significantly influenced by SMF. Higher activities of intracellular key enzymes were determined (with 95.0 mT SMF) as responsible for better decolorization and COD removal performances. Bacteria belonging to Prolixibacter, Corynebacterium, Pelagibacterium, Demequina, and Sphingobacterium which might be responsible for azo dye decolorization and aromatic compounds biodegradation were significantly enriched only in presence of SMF. Fungal genera Candida and Pichia were also significantly enriched by 41.4-305.0 mT SMF, which might be responsible for higher treatment efficiency. PRACTITIONER POINTS: Dye degradation was enhanced by combination of static magnetic field and yeasts. Improvement of enzyme activity was responsible for better treatment performance. Putative azo-degrading-related bacteria and fungi were selectively enriched. High relative abundance of Candida and Pichia ensured high decolorization effects. Potentially effective improvement of bioprocesses for treating hypersaline wastewater.

Benzene homologues contaminants in a former herbicide factory site: distribution, attenuation, risk, and remediation implication

Benzene homologues often used as organic raw materials or as detergents in chemical industry are prone to accidental release into the environment which can cause serious long-term soil pollutions. In a large former herbicide factory site, we investigated 43 locations for benzene homologues contaminations in soil, soil gas, and groundwater and studied the hydrogeological conditions. An inverse distance weighted interpolation method was employed to determine the pollutants three-dimensional spatial distribution in the soils. Results showed that benzene homologues residues were mainly originated from the herbicide production workshop and that the pollution had horizontally expanded at the deeper soil layer. Contaminants had already migrated 15 m downward from ground surface. Contaminant phase distribution study showed that NAPL was the primary phase (> 99%) for the pollutants accumulated in the unsaturated zone, while it had not migrated to groundwater. The primary mechanism for contaminant transport and attenuation included dissolution of "occluded" NAPL into pore water and pollutant volatilization into soil pore space. Risk assessment revealed that the pollutants brought unacceptable high carcinogenic and non-carcinogenic risks to public health. In order to convert this former chemical processing factory site into a residential area, a remediation to the polluted production workshop sites is urgently required.

Estructura y función de las oxigenasas tipo Rieske/mononuclear

Las oxigenasas Rieske/mononuclear son un grupo de metaloenzimas que catalizan la oxidación de una variedad de compuestos, destaca su participación en la degradación de compuestos xenobióticos contaminantes; estas enzimas también participan en la biosíntesis de algunos compuestos de interés comercial. Poseen una amplia especificidad por el sustrato, convirtiéndolas en un grupo de enzimas con un alto potencial de aplicación en procesos biotecnológicos que hasta el momento no ha sido explotado. La presente revisión aborda aspectos generales acerca de la función y estructura de este importante grupo de enzimas. 

Enhancement of facultative anaerobic denitrifying communities by oxygen release from roots of the macrophyte in constructed wetlands

The radial oxygen loss (ROL) of wetland plants is a crucial factor that can influence the efficiency required for nitrogen (N) removal and microbial activities responsible for N removal in constructed wetlands (CWs). However, the shift of microbial community in different niches in response to ROL has been rarely studied. This study aims to unravel the link between the ROL and microbial response in sediment, water and rhizoplane by a surface flow CW planted with Myriophyllum aquaticum for treating high-strength swine wastewater. Ti³⁺-citrate colorimetric method demonstrated that M. aquaticum was a wetland species with a ROL of 0.019 mg/h/plant. Using quantitative polymerase chain reactions (qPCR) and high-throughput sequencing of microbial 16S rRNA gene, we demonstrated that the abundance of facultative anaerobic denitrifiers in the rhizoplane was the most of the three niches, that in the water (5-10 cm) was the less and that in the sediment was the least. Acinetobacter was enriched and dominated amongst denitrifiers in the water. Denitrifiers in the rhizoplane were mainly dominated by enriched Pseudomonas, Aeromonas, and Acinetobacter. The theoretical calculation of oxygen sources and consumptions indicated that water reaeration should support the oxygen demands for nitrification in the aerobic layer (0-5 cm), and the ROL could stimulate the growth of facultative anaerobic denitrifiers in the rhizoplane and water (5-10 cm) to achieve denitrification within CW systems.

Bacterial Diversity and the Geochemical Landscape in the Southwestern Gulf of Mexico

Marine sediments are an example of one of the most complex microbial habitats. These bacterial communities play an important role in several biogeochemical cycles in the marine ecosystem. In particular, the Gulf of Mexico has a ubiquitous concentration of hydrocarbons in its sediments, representing a very interesting niche to explore. Additionally, the Mexican government has opened its oil industry, offering several exploration and production blocks in shallow and deep water in the southwestern Gulf of Mexico (swGoM), from which there are no public results of conducted studies. Given the higher risk of large-scale oil spills, the design of contingency plans and mitigation activities before oil exploitation is of growing concern. Therefore, a bacterial taxonomic baseline profile is crucial to understanding the impact of any eventual oil spill. Here, we show a genus level taxonomic profile to elucidate the bacterial baseline, pointing out richness and relative abundance, as well as relationships with 79 abiotic parameters, in an area encompassing ∼150,000 km2, including a region where the exploitation of new oil wells has already been authorized. Our results describe for the first time the bacterial landscape of the swGoM, establishing a bacterial baseline "core" of 450 genera for marine sediments in this region. We can also differentiate bacterial populations from shallow and deep zones of the swGoM based on their community structure. Shallow sediments have been chronically exposed to aromatic hydrocarbons, unlike deep zones. Our results reveal that the bacterial community structure is particularly enriched with hydrocarbon-degrading bacteria in the shallow zone, where a greater aromatic hydrocarbon concentration was determined. Differences in the bacterial communities in the swGoM were also observed through a comprehensive comparative analysis relative to various marine sediment sequencing projects, including sampled sites from the Deep Water Horizon oil spill. This study in the swGoM provides clues to the bacterial population adaptation to the ubiquitous presence of hydrocarbons and reveals organisms such as Thioprofundum bacteria with potential applications in ecological surveillance. This resource will allow us to differentiate between natural conditions and alterations generated by oil extraction activities, which, in turn, enables us to assess the environmental impact of such activities.

Investigation into the nitrate removal efficiency and microbial communities in a sequencing batch reactor treating reverse osmosis concentrate produced by a coking wastewater treatment plant

In this study, a biological denitrifying process using a sequencing batch reactor (SBR) was employed to treat reverse osmosis (RO) concentrate with high conductivity produced from a coking wastewater plant. From the results, the average removal efficiencies for chemical oxygen demand, total nitrogen, and nitrate were 79.5%, 90.5%, and 93.1%, respectively. Different microbial communities were identified after sequencing the V1-V3 region of the 16S rRNA gene using the MiSeq platform, and the major bacterial phyla in the SBR system were Proteobacteria and Bacteroidetes. The main microorganisms responsible for denitrification were from the genera Hyphomicrobium, Thauera, Methyloversatilis, and Rhodobacter. Quantitative real-time PCR was used to quantify the absolute levels of denitrifying genes, including narG, nirS, nirK, and nosZ, during the start-up and stable operation of the SBR. The abundances of narG, nirK, and nosZ were lower during stable operation than those in the start-up period. The abundance of nirS at a concentration of 10⁴-10⁵ copies/ng in DNA was much higher than that of nirK, making it the dominant functional gene responsible for nitrite reduction. The higher nitrate removal efficiency suggests that biological denitrification using SBR is an effective technique for treating RO concentrate produced from coking wastewater plants.

Comprehensive review on toxicity of persistent organic pollutants from petroleum refinery waste and their degradation by microorganisms

Control and prevention of environmental pollution has become a worldwide issue of concern. Aromatic hydrocarbons including benzene, toluene, ethyl benzene, xylene (BTEX) and polyaromatic hydrocarbons (PAHs) are persistent organic pollutants (POPs), released into the environment mainly by exploration activities of petroleum industry. These pollutants are mutagenic, carcinogenic, immunotoxic and teratogenic to lower and higher forms of life i.e. microorganisms to humans. According to the International Agency for Research on Cancer (IARC) and United States Environmental Protection Agency (U.S. EPA), Benzo[a]pyrene (BaP) is carcinogenic in laboratory animals and humans. Aromatic hydrocarbons are highly lipid soluble and thus readily absorbed from environment in gastrointestinal tract of mammals. Treatment and remediation of petroleum refinery waste have been shown either to reduce or to eliminate genotoxicity of these pollutants. Bioremediation by using microorganisms to treat this waste is showing a promising technology as it is safe and cost-effective option among various technologies tested. The main aim of this review is to provide contemporary information on variety of aromatic hydrocarbons present in crude oil (with special focus to mono- and poly-aromatic hydrocarbons), exposure routes and their adverse effects on humans. This review also provides a synthesis of scientific literature on remediation technologies available for aromatic hydrocarbons, knowledge gaps and future research developments in this field.

Bacterial communities associated with anaerobic debromination of decabromodiphenyl ether from mangrove sediment

This study evaluated decabromodiphenyl ether (BDE-209) anaerobic debromination and bacterial community changes in mangrove sediment. BDE-209 debromination rates were enhanced with zerovalent iron compared to without zerovalent iron in the sediment. BDE-209 debromination rates in microcosms constructed with sediments collected in autumn were higher than in microcosms constructed with sediments collected in spring and were higher at the Bali sampling site than the Guandu sampling site. The intermediate products resulting from the reductive debromination of BDE-209 in sediment were nona-BDE (BDE-206, BDE-207), octa-BDEs (BDE-196, BDE-197), hepta-BDEs (BDE-183, BDE-184, BDE-191), hexa-BDEs (BDE-137, BDE-138, BDE-154, BDE-157), penta-BDEs (BDE-85, BDE-99, BDE-100, BDE-126), tetra-BDEs (BDE-47, BDE-49, BDE-66, BDE-77), tri-BDEs (BDE-17, BDE-28), and di-BDEs (BDE-15). Fifty bacterial genera associated with BDE-209 debromination were identified. Overall, 12 of the 50 bacterial genera were reported to be involved in dehalogenation of aromatic compounds. These bacteria have high potential to be BDE-209 debromination bacteria. Different combinations of bacterial community composition exhibit different abilities for BDE-209 anaerobic debromination.

Ectoine and 5-hydroxyectoine accumulation in the halophile Virgibacillus halodenitrificans PDB-F2 in response to salt stress

The moderately halophilic bacterium Virgibacillus halodenitrificans PDB-F2 copes with salinity by synthesizing or taking up compatible solutes. The main compatible solutes in this strain were ectoine and hydroxyectoine, as determined by (1)H nuclear magnetic resonance spectroscopy ((1)H-NMR). A high-performance liquid chromatography (HPLC) analysis showed that ectoine was the major solute that was synthesized in response to elevated salinity, while hydroxyectoine was a minor solute. However, the hydroxyectoine/ectoine ratio increased from 0.04 at 3 % NaCl to 0.45 at 15 % NaCl in the late exponential growth phase. A cluster of ectoine biosynthesis genes was identified, including three genes in the order of ectA, ectB, and ectC. The hydroxyectoine biosynthesis gene ectD was not part of the ectABC gene cluster. Reverse transcription-quantitative polymerase chain reactions (RT-qPCR) showed that the expression of the ect genes was salinity dependent. The expression of ectABC reached a maximum at 12 % NaCl, while ectD expression increased up to 15 % NaCl. Ectoine and hydroxyectoine production was growth phase dependent. The hydroxyectoine/ectoine ratio increased from 0.018 in the early exponential phase to 0.11 in the stationary phase at 5 % NaCl. Hydroxyectoine biosynthesis started much later than ectoine biosynthesis after osmotic shock, and the temporal expression of the ect genes differed under these conditions, with the ectABC genes being expressed first, followed by ectD gene. Increased culture salinity triggered ectoine or hydroxyectoine uptake when they were added to the medium. Hydroxyectoine was accumulated preferentially when both ectoine and hydroxyectoine were provided exogenously.

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.