Bio-oxidation of elemental mercury during growth of mercury resistant yeasts in simulated hydrosphere

Comparative analysis of species-specific dissolved gaseous mercury oxidation in phytoplankton cultures

Phytoplankton species influence mercury cycling through bioaccumulation and Hg(II) reduction, however their contribution to oxidation of Hg(0) in aquatic systems remains largely overlooked. The present study aims at investigating the oxidation of Hg(0) by two phytoplankton species: the diatom Cyclotella meneghiniana and the green alga Chlamydomonas reinhardtii. The algae were exposed to gaseous Hg(0) at concentrations in the range of 6-12 μg m-3, representative for contaminated environments, under various experimental conditions (open vs. closed systems, light vs dark, and alive vs dead cells). The obtained results revealed, for a first time, that Hg(0) oxidation in C. meneghiniana cultures was light-dependent and limited to live cells, whereas C. reinhardtii maintained similar oxidation rates in both live and dead cells. C. reinhardtii cultures exhibited nearly tenfold higher Hg(0) oxidation efficiency than C. meneghiniana, demonstrating a strong species-dependent effect. Both species facilitated Hg(0) uptake from air into water, demonstrating a potential route for atmospheric Hg(0) to enter aquatic food webs. This novel evidence of phytoplankton-mediated Hg(0) oxidation highlights the importance of species identity and environmental conditions in governing Hg transformations and bioavailability. The results could have significant implications for understanding mercury bioaccumulation and toxicity in aquatic ecosystems. Further research is needed to clarify their contribution to Hg(0) oxidation in aquatic systems and to elucidate the underlying mechanisms driving the process.

Reactive Fluorescent and Colorimetric Probe for Highly Selective and Sensitive Detection of Hg2+ in Real Water Samples

Construction of efficient chemosensors for highly specific and sensitive detection of mercury ions remains a great challenge. In this work a highly selective and sensitive probe CY was designed and synthesized by using coumarin fluorophore as the matrix and thioacetal moiety as the reactive recognition site for Hg2+. By virtue of the thiophilicity of Hg2+, probe CL could be hydrolyzed to deprotect and the thioacetal was transformed to the acyl group after the addition of Hg2+, the blue-green fluorescence was quenched and meanwhile the solution changed from light green to yellow. The detection limit of probe CY for Hg2+ was as low as 6.8 nM, and it could completely react with Hg2+ within 3 min. Moreover, probe CY exhibited good resistance against interference from competitive metal ions and biothiols, high stability in pH 1-11 and applicability for fluorogenic and chromogenic dual-modal detection of Hg2+ in real water samples over a broad range of pH 5-10.

Understanding the risks of mercury sulfide nanoparticles in the environment: Formation, presence, and environmental behaviors

Mercury (Hg) could be microbially methylated to the bioaccumulative neurotoxin methylmercury (MeHg), raising health concerns. Understanding the methylation of various Hg species is thus critical in predicting the MeHg risk. Among the known Hg species, mercury sulfide (HgS) is the largest Hg reservoir in the lithosphere and has long been considered to be highly inert. However, with advances in the analytical methods of nanoparticles, HgS nanoparticles (HgS NPs) have recently been detected in various environmental matrices or organisms. Furthermore, pioneering laboratory studies have reported the high bioavailability of HgS NPs. The formation, presence, and transformation (e.g., methylation) of HgS NPs are intricately related to several environmental factors, especially dissolved organic matter (DOM). The complexity of the behavior of HgS NPs and the heterogeneity of DOM prevent us from comprehensively understanding and predicting the risk of HgS NPs. To reveal the role of HgS NPs in Hg biogeochemical cycling, research needs should focus on the following aspects: the formation pathways, the presence, and the environmental behaviors of HgS NPs impacted by the dominant influential factor of DOM. We thus summarized the latest progress in these aspects and proposed future research priorities, e.g., developing the detection techniques of HgS NPs and probing HgS NPs in various matrices, further exploring the interactions between DOM and HgS NPs. Besides, as most of the previous studies were conducted in laboratories, our current knowledge should be further refreshed through field observations, which would help to gain better insights into predicting the Hg risks in natural environment.

A comprehensive assessment of Yarrowia lipolytica and its interactions with metals: Current updates and future prospective

The non-conventional yeast Yarrowia lipolytica has been popular as a model system for understanding biological processes such as dimorphism and lipid accumulation. The organism can efficiently utilize hydrophobic substrates (hydrocarbons and triglycerides) thereby rendering it relevant in bioremediation of oil polluted environments. The current review focuses on the interactions of this fungus with metal pollutants and its potential application in bioremediation of metal contaminated locales. This fungus is intrinsically equipped with a variety of physiological and biochemical features that enable it to tide over stress conditions induced by the presence of metals. Production of enzymes such as phosphatases, reductases and superoxide dismutases are worth a special mention. In the presence of metals, levels of inherently produced metal binding proteins (metallothioneins) and the pigment melanin are seen to be elevated. Morphological alterations with respect to biofilm formation and dimorphic transition from yeast to mycelial form are also induced by certain metals. The biomass of Y. lipolytica is inherently important as a biosorbent and cell surface modification, process optimization or whole cell immobilization techniques have aided in improving this capability. In the presence of metals such as mercury, cadmium, copper and uranium, the culture forms nanoparticulate deposits. In addition, on account of its intrinsic reductive ability, Y. lipolytica is being exploited for synthesizing nanoparticles of gold, silver, cadmium and selenium with applications as antimicrobial compounds, location agents for bioimaging and as feed supplements. This versatile organism thus has great potential in interacting with various metals and addressing problems related to their pollutant status.