Bioremediation of toxic substances by mercury resistant marine bacteria

Using a food web model to predict the effects of Hazardous and Noxious Substances (HNS) accidental spills on deep-sea hydrothermal vents from the Mid-Atlantic Ridge (MAR) region

Deep-sea hydrothermal vents host unique ecosystems but face risks of incidents with Hazardous and Noxious Substances (HNS) along busy shipping lanes such as the transatlantic route. We developed an Ecopath with Ecosim (EwE) model of the Menez Gwen (MG) vent field (MG-EwE) (Mid-Atlantic Ridge) to simulate ecosystem effects of potential accidental spills of four different HNS, using a semi-Lagrangian Dispersion Model (sLDM) coupled with the Regional Ocean Modelling System (ROMS) calibrated for the study area. Food web modelling revealed a simplified trophic structure with low energy efficiency. The MG ecosystem was vulnerable to disruptions caused by all tested HNS, yet it revealed some long-term resilience. Understanding these impacts is vital for enhancing Spill Prevention, Control, and Countermeasure plans (SPCC) in remote marine areas and developing tools to assess stressors effects on these invaluable habitats.

Microbial community structure and metabolic potential in the coastal sediments around the Yellow River Estuary

The Yellow River Estuary and Laizhou Bay are located on the northern Shandong Peninsula in the Bohai Sea in China and have been polluted by intensive anthropogenic activity. However, few studies have focused on the effect of these activities on the microbial communities and their ecological functions in this area. In this study, the combination of 16S rDNA gene sequencing and GeoChip technology was used to analyzed the microbial community component and their functional genes. Thaumarchaeot and Bacteroidetes are the most abundant phyla. The results of correlation analysis and redundancy analysis (RDA) showed water depth (r² = 0.76, P = 0.005), total Na content (r² = 0.63, P = 0.021) and total Ca content (r² = 0.53, P = 0.05) in the sediments were the most significant environmental factors affecting the microbial community. The diversity of the microbial community and signal intensity of functional genes at nearshore sites (N sites) were higher than that at the offshore sites (O sites), but the component of microbial community and functional genes was similar in general. Functional genes for C, N, P and S cycle were detected at both nearshore and offshore sites, which illustrated that microbial communities were active in nutrient cycle. Proteobacteria contributes significantly to material cycle in microbial community. In addition, functional genes related to organic remediation and metal detoxification are also abundant. It indicated that the environmental pollution caused by anthropogenic activities has greatly affected the microbial community components and their biochemical functions in the Yellow River Estuary and surrounding areas. This study reveals the effect of anthropogenic activities on microbial communities and provides the basis for environmental management.

Bismuth-based photocatalyst for photocatalytic oxidation of flue gas mercury removal: A review

Photocatalytic oxidation method is a promising technology for solving flue gas mercury (Hg) pollution from industrial plants. Semiconductor photocatalysts have been widely applied in energy conversion and environmental remediation. However, key issues such as low light absorption capacity, wide energy band gap, and poor physicochemical stability severely limit the application of photocatalysts in practical industrial plants. In recent years, bismuth-based (Bi-based) photocatalysts, including bismuth oxide halide BiOX (X = Cl, Br or I), bismuth salt oxymetal BiVO₄, and BiOIO₃ etc., have increasingly aroused scientists' attention due to their peculiar crystalline geometric structures, tunable electronic structure and high photocatalytic performance. In present review, we firstly review the photocatalytic reaction mechanism and main photocatalytic oxidation mechanism of mercury. Secondly, the synthetic methods of Bi-based photocatalysts are summarized. Then, according to the mechanism of mercury removal, the experimental modifying approaches including heterojunction making, external atoms doping, defect creating, and crystal face regulating to promote the photocatalytic oxidation of mercury removal are summarized, as well as the determination of the band gap and electronic density of states (DOS) of Bi-based photocatalysts to elucidate the photocatalytic oxidation mechanism via density functional theory (DFT) calculation. Furthermore, constructing electronic transmission channels is an efficient way to improve the photocatalytic activity. Finally, challenges and perspectives of Bi-based photocatalyst for photocatalytic oxidation of mercury removal are presented. In addition, the excellent performance photocatalysts and efficient pollution removal equipment for mercury removal in industrial plants are still required in-depth study.

Acinetobacter calcoaceticus CSY-P13 Mitigates Stress of Ferulic and p-Hydroxybenzoic Acids in Cucumber by Affecting Antioxidant Enzyme Activity and Soil Bacterial Community

Ferulic acid (FA) and p-hydroxybenzoic acid (PHBA) are main phenolic compounds accumulated in rhizosphere of continuously cropped cucumber, causing stress in plants. Microbial degradation of a mixture of FA and PHBA is not well understood in soil. We isolated a strain CSY-P13 of Acinetobacter calcoaceticus, inoculated it into soil to protect cucumber from FA and PHBA stress, and explored a mechanism underlying the protection. CSY-P13 effectively degraded a mixture of FA and PHBA in culture solution under conditions of 39.37°C, pH 6.97, and 21.59 g L-1 potassium dihydrogen phosphate, giving rise to 4-vinyl guaiacol, vanillin, vanillic acid, and protocatechuic acid. During FA and PHBA degradation, activities of superoxide dismutase (SOD), catalase, ascorbate peroxidase, and dehydroascorbate reductase in CSY-P13 were induced. Inoculated into cucumber-planted soil containing 220 μg g-1 mixture of FA and PHBA, CSY-P13 degraded FA and PHBA in soil, increased plant height, and decreased malonaldehyde, superoxide radical, and hydrogen peroxide levels in leaves. CSY-P13 also enhanced SOD, guaiacol peroxidase, catalase, glutathione peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase activities; increased ascorbate and glutathione contents; and elevated transcript levels of copper/zinc SOD, manganese SOD, and catalase in leaves under FA and PHBA. Moreover, CSY-P13 increased phosphatase, catalase, urease, and sucrase activities and changed bacterial richness, diversity, and community composition by high throughput sequencing in cucumber-planted soil supplemented with the mixture of FA and PHBA. So CSY-P13 degrades the mixture of FA and PHBA in soil and mitigates stress from the two phenolic compounds in cucumber by activating antioxidant enzymes, changing soil bacterial community, and inducing soil enzymes.

Mercury bioremediation by mercury accumulating Enterobacter sp. cells and its alginate immobilized application

The effective microbial remediation of the mercury necessitates the mercury to be trapped within the cells without being recycled back to the environment. The study describes a mercury bioaccumulating strain of Enterobacter sp., which remediated mercury from the medium simultaneous to its growth. The transmission electron micrographs and electron dispersive X-ray analysis revealed the accumulation of remediated mercury as nano-size particles in the cytoplasm as well as on the cell wall. The Enterobacter sp. in the present work was able to accumulate mercury, without being engineered in its native form. The possibility of recovering the accumulated mercury from the cells is also indicated. The applicability of the alginate immobilized cells in removing mercury from synthetic and complex industrial effluent in a batch mode was amply demonstrated. The initial load of 7.3 mg l(-1) mercury in the industrial effluent was completely removed in 72 h. The cells immobilized in calcium alginate were similarly effective in the complete removal of 5 mg l(-1) HgCl(2) of mercury from the synthetic effluent in less than 72 h. The immobilized cells could be reused for multiple cycles.

Arsenite tolerance and biotransformation potential in estuarine bacteria

Bacterial isolates from water and sediment samples from freshwater, estuarine and marine regions were tested for their growth in the presence of different concentrations of arsenic. Despite the generation times being longer in case of all bacterial isolates tested in nutrient broth with 200 ppm Arsenite (As(3+)), many of them were able to attain log phase and substantial growth variously between 36 and 96 h. The isolates tolerating >or=200 ppm arsenic (As) were found to belong to Enterobacteriaceae, Pseudomonas, Corynebaterium, Xanthomonas, Acinetobacter, Flavimonas and Micrococcus. Some of these environmental strains tolerant to 1,000 ppm arsenic were tested to realize their potential to detoxify arsenic. The rate of As biotransformation was faster by many of these strains. The percent of arsenite biotransformed/removed from the growth medium was the highest by a strain of Enterobacteriaceae (as much as 92% of the As in the growth medium by 120 h) followed by that of Corynebaterium and Acinetobacter strains. From these observations it is clear that many environmental strains are capable of quite rapid biotransformation of As. Contamination of drinking water by toxic metalloid arsenic affects thousands of people worldwide. Many environmental isolates of bacteria which detoxify this metalloid would serve beneficial in the depuration processes. We suggest that only such strains capable of high tolerance to toxic arsenite, would biotransform As in polluted estuarine environments and would prove useful in As bioremediation applications.

Detoxification of toxic heavy metals by marine bacteria highly resistant to mercury

Pollution in industrial areas is a serious environmental concern, and interest in bacterial resistance to heavy metals is of practical significance. Mercury (Hg), Cadmium (Cd), and lead (Pb) are known to cause damage to living organisms, including human beings. Several marine bacteria highly resistant to mercury (BHRM) capable of growing at 25 ppm (mg L(-1)) or higher concentrations of mercury were tested during this study to evaluate their potential to detoxify Cd and Pb. Results indicate their potential of detoxification not only of Hg, but also Cd and Pb. Through biochemical and 16S rRNA gene sequence analyses, these bacteria were identified to belong to Alcaligenes faecalis (seven isolates), Bacillus pumilus (three isolates), Bacillus sp. (one isolate), Pseudomonas aeruginosa (one isolate), and Brevibacterium iodinium (one isolate). The mechanisms of heavy metal detoxification were through volatilization (for Hg), putative entrapment in the extracellular polymeric substance (for Hg, Cd and Pb) as revealed by the scanning electron microscopy and energy dispersive x-ray spectroscopy, and/or precipitation as sulfide (for Pb). These bacteria removed more than 70% of Cd and 98% of Pb within 72 and 96 h, respectively, from growth medium that had initial metal concentrations of 100 ppm. Their detoxification efficiency for Hg, Cd and Pb indicates good potential for application in bioremediation of toxic heavy metals.