An Overview of Bacteria-Mediated Heavy Metal Bioremediation Strategies

Contamination-free groundwater is considered a good source of potable water. Even in the twenty-first century, over 90 percent of the population is reliant on groundwater resources for their lives. Groundwater influences the economical state, industrial development, ecological system, and agricultural and global health conditions worldwide. However, different natural and artificial processes are gradually polluting groundwater and drinking water systems throughout the world. Toxic metalloids are one of the major sources that pollute the water system. In this review work, we have collected and analyzed information on metal-resistant bacteria along with their genetic information and remediation mechanisms of twenty different metal ions [arsenic (As), mercury (Hg), lead (Pb), chromium (Cr), iron (Fe), copper (Cu), cadmium (Cd), palladium (Pd), zinc (Zn), cobalt (Co), antimony (Sb), gold (Au), silver (Ag), platinum (Pt), selenium (Se), manganese (Mn), molybdenum (Mo), nickel (Ni), tungsten (W), and uranium (U)]. We have surveyed the scientific information available on bacteria-mediated bioremediation of various metals and presented the data with responsible genes and proteins that contribute to bioremediation, bioaccumulation, and biosorption mechanisms. Knowledge of the genes responsible and self-defense mechanisms of diverse metal-resistance bacteria would help us to engineer processes involving multi-metal-resistant bacteria that may reduce metal toxicity in the environment.

Mechanism of vanadium(IV) resistance of the strains isolated from a vanadium titanomagnetite mining region

Microbial treatment for vanadium contamination of soils is a favorable and environment-friendly method. However, information of the resistant mechanism of the strains in soils to vanadium, especially to tetravalent vanadium [vanadium(IV)], is still limited. Herein, potential of the vanadium(IV) biosorption and biotransformation of the strains (4K1, 4K2, 4K3 and 4K4) which were capable of tolerating vanadium(IV) was determined. For biosorption, the bioadsorption and the bioabsorption of vanadium(IV) occur on the bacterial cell wall and within the cell, respectively, were taken into consideration. Comparison of the vanadium(IV) adsorbed on the bacterial cell walls and remained in the cells after sorption indicated the major bacterial vanadium(IV) sorption role of the bioadsorption which was at least one order of magnitude higher than the bioabsorption amount. Isotherm study using various isotherm models revealed a monolayer and a multilayer vanadium(IV) biosorption by 4K2 and the others (4K1, 4K3 and 4K4), respectively. Higher biosorption was observed in acidic conditions than in alkaline conditions, and the maximum biosorption was 2.41, 9.35, 7.76 and 8.44 mg g^-1 observed at pH 6 for 4K1, at pH 3 for 4K2, and at pH 4 for 4K3 and 4K4, respectively. At the present experimental range of the initial vanadium(IV) concentration, optimal biosorption capacity of the bacteria was observed at the vanadium(IV) level of 100-250 mg L^-1. Different biotransformation level of vanadium(IV) in soils by the stains was observed during a 28-d pot incubation of the soils mixed with the strains, which can be attributed to the discrepancy of both soil properties and bacterial species. Present study can help to fill up the gaps of the insufficient knowledge of the vanadium(IV) resistant mechanism of the strains in soils.

Current bone substitutes for implant dentistry

PURPOSE

Alveolar ridge augmentation is essential for success in implant therapy and depends on the biological performance of bone graft materials. This literature review aims to comprehensively explain the clinically relevant capabilities and limitations of currently available bone substitutes for bone augmentation in light of biomaterial science.

STUDY SELECTION

The biological performance of calcium phosphate-based bone substitutes was categorized according to space-making capability, biocompatibility, bioabsorption, and volume maintenance over time. Each category was reviewed based on clinical studies, preclinical animal studies, and in vitro studies.

RESULTS

Currently available bone substitutes provide only osteoconduction as a scaffold but not osteoinduction. Particle size, sensitivity to enzymatic or chemical dissolution, and mechanical properties affect the space-making capability of bone substitutes. The nature of collagen fibers, particulate size, and release of calcium ions influence the biocompatibility of bone substitutes. Bioabsorption of bone substitutes is determined by water solubility (chemical composition) and acid resistance (integrity of apatite structure). Bioabsorption of remnant bone substitute material and volume maintenance of the augmented bone are inversely related.

CONCLUSION

It is necessary to improve the biocompatibility of currently available bone substitutes and to strike an appropriate balance between bioabsorption and volume maintenance to achieve ideal bone remodeling.

Promotion of airway anastomotic microvascular regeneration and alleviation of airway ischemia by deferoxamine nanoparticles

Airway tissue ischemia and hypoxia in human lung transplantation is a consequence of the sacrifice of the bronchial circulation during the surgical procedure and is a major risk factor for the development of airway anastomotic complications. Augmented expression of hypoxia-inducible factor (HIF)-1α promotes microvascular repair and alleviates allograft ischemia and hypoxia. Deferoxamine mesylate (DFO) is an FDA-approved iron chelator which has been shown to upregulate cellular HIF-1α. Here, we developed a nanoparticle formulation of DFO that can be topically applied to airway transplants at the time of surgery. In a mouse orthotopic tracheal transplant (OTT) model, the DFO nanoparticle was highly effective in enhancing airway microvascular perfusion following transplantation through the production of the angiogenic factors, placental growth factor (PLGF) and stromal cell-derived factor (SDF)-1. The endothelial cells in DFO treated airways displayed higher levels of p-eNOS and Ki67, less apoptosis, and decreased production of perivascular reactive oxygen species (ROS) compared to vehicle-treated airways. In summary, a DFO formulation topically-applied at the time of surgery successfully augmented airway anastomotic microvascular regeneration and the repair of alloimmune-injured microvasculature. This approach may be an effective topical transplant-conditioning therapy for preventing airway complications following clinical lung transplantation.