Hydrogen enhances nickel tolerance in the purple sulfur bacterium Thiocapsa roseopersicina

Bacterial metal(loid) resistance genes (MRGs) and their variation and application in environment: A review

Toxic metal(loid)s are widespread and permanent in the biosphere, and bacteria have evolved a wide variety of metal(loid) resistance genes (MRGs) to resist the stress of excess metal(loid)s. Via active efflux, permeability barriers, extracellular/intracellular sequestration, enzymatic detoxification and reduction in metal(loid)s sensitivity of cellular targets, the key components of bacterial cells are protected from toxic metal(loid)s to maintain their normal physiological functions. Exploiting bacterial metal(loid) resistance mechanisms, MRGs have been applied in many environmental fields. Based on the specific binding ability of MRGs-encoded regulators to metal(loid)s, MRGs-dependent biosensors for monitoring environmental metal(loid)s are developed. MRGs-related biotechnologies have been applied to environmental remediation of metal(loid)s by using the metal(loid) tolerance, biotransformation, and biopassivation abilities of MRGs-carrying microorganisms. In this work, we review the historical evolution, resistance mechanisms, environmental variation, and environmental applications of bacterial MRGs. The potential hazards, unresolved problems, and future research directions are also discussed.

The Microbiology of Metal Mine Waste: Bioremediation Applications and Implications for Planetary Health

Mine wastes pollute the environment with metals and metalloids in toxic concentrations, causing problems for humans and wildlife. Microorganisms colonize and inhabit mine wastes, and can influence the environmental mobility of metals through metabolic activity, biogeochemical cycling and detoxification mechanisms. In this article we review the microbiology of the metals and metalloids most commonly associated with mine wastes: arsenic, cadmium, chromium, copper, lead, mercury, nickel and zinc. We discuss the molecular mechanisms by which bacteria, archaea, and fungi interact with contaminant metals and the consequences for metal fate in the environment, focusing on long-term field studies of metal-impacted mine wastes where possible. Metal contamination can decrease the efficiency of soil functioning and essential element cycling due to the need for microbes to expend energy to maintain and repair cells. However, microbial communities are able to tolerate and adapt to metal contamination, particularly when the contaminant metals are essential elements that are subject to homeostasis or have a close biochemical analog. Stimulating the development of microbially reducing conditions, for example in constructed wetlands, is beneficial for remediating many metals associated with mine wastes. It has been shown to be effective at low pH, circumneutral and high pH conditions in the laboratory and at pilot field-scale. Further demonstration of this technology at full field-scale is required, as is more research to optimize bioremediation and to investigate combined remediation strategies. Microbial activity has the potential to mitigate the impacts of metal mine wastes, and therefore lessen the impact of this pollution on planetary health.

Isotopic fractionation associated with [NiFe]- and [FeFe]-hydrogenases

RATIONALE

Hydrogenases catalyze the reversible formation of H2 from electrons and protons with high efficiency. Understanding the relationships between H2 production, H2 uptake, and H2-H2O exchange can provide insight into the metabolism of microbial communities in which H2 is an essential component in energy cycling.

METHODS

We used stable H isotopes (1H and 2H) to probe the isotope effects associated with three [FeFe]-hydrogenases and three [NiFe]-hydrogenases.

RESULTS

All six hydrogenases displayed fractionation factors for H2 formation that were significantly less than 1, producing H2 that was severely depleted in 2H relative to the substrate, water. Consistent with differences in their active site structure, the fractionation factors for each class appear to cluster, with the three [NiFe]-hydrogenases (α = 0.27–0.40) generally having smaller values than the three [FeFe]-hydrogenases (α = 0.41–0.55). We also obtained isotopic fractionation factors associated with H2 uptake and H2-H2O exchange under conditions similar to those utilized for H2 production, providing a more complete picture of the reactions catalyzed by hydrogenases.

CONCLUSIONS

The fractionation factors determined in our studies can be used as signatures for different hydrogenases to probe their activity under different growth conditions and to ascertain which hydrogenases are most responsible for H2 production and/or uptake in complex microbial communities.

Palladium nanoparticles produced and dispersed by Caldicellulosiruptor saccharolyticus enhance the degradation of contaminants in water

This study focused on examining the general applicability of coupling bio-palladium (Pd) nanoparticle generation and bio-H₂ produced by Caldicellulosiruptor saccharolyticus for wastewater treatment under extreme thermophilic conditions.

Mechanisms of nickel toxicity in microorganisms

Nickel has long been known to be an important human toxicant, including having the ability to form carcinomas, but until recently nickel was believed to be an issue only to microorganisms living in nickel-rich serpentine soils or areas contaminated by industrial pollution. This assumption was overturned by the discovery of a nickel defense system (RcnR/RcnA) found in microorganisms that live in a wide range of environmental niches, suggesting that nickel homeostasis is a general biological concern. To date, the mechanisms of nickel toxicity in microorganisms and higher eukaryotes are poorly understood. In this review, we summarize nickel homeostasis processes used by microorganisms and highlight in vivo and in vitro effects of exposure to elevated concentrations of nickel. On the basis of this evidence we propose four mechanisms of nickel toxicity: (1) nickel replaces the essential metal of metalloproteins, (2) nickel binds to catalytic residues of non-metalloenzymes; (3) nickel binds outside the catalytic site of an enzyme to inhibit allosterically and (4) nickel indirectly causes oxidative stress.

Photo-induced H2 production by [NiFe]-hydrogenase from T. roseopersicina covalently linked to a Ru(II) photosensitizer

The potential of hydrogen as a clean renewable fuel source and the finite reserves of platinum metal to be utilized in hydrogen production catalysts have provided the motivation for the development of non-noble metal-based solutions for catalytic hydrogen production. There are a number of microorganisms that possess highly efficient hydrogen production catalysts termed hydrogenases that generate hydrogen under certain metabolic conditions. Although hydrogenases occur in photosynthetic microorganisms, the oxygen sensitivity of these enzymes represents a significant barrier in directly coupling hydrogen production to oxygenic photosynthesis. To overcome this barrier, there has been considerable interest in identifying or engineering oxygen tolerant hydrogenases or generating mimetic systems that do not rely on oxygen producing photocatalysts. In this work, we demonstrate photo-induced hydrogen production from a stable [NiFe]-hydrogenase coupled to a [Ru(2,2'-bipyridine)(2)(5-amino-1,10-phenanthroline)](2+) photocatalyst. When the Ru(II) complex is covalently attached to the hydrogenase, photocatalytic hydrogen production occurs more efficiently in the presence of a redox mediator than if the Ru(II) complex is simply present in solution. Furthermore, sustained hydrogen production occurs even in the presence of oxygen by presumably creating a local anoxic environment through the reduction of oxygen similar to what is proposed for oxygen tolerant hydrogenases. These results provide a strong proof of concept for engineering photocatalytic hydrogen production in the presence of oxygen using biohybrid mimetic systems.