Uptake and transformation of metals and metalloids by microbial mats and their use in bioremediation

Summary Constructed microbial mats, used for studies on the removal and transformation of metals and metalloids, are made by combining cyanobacteria inoculum with a sediment inoculum from a metal-contaminated site. These mats are a heterotrophic and autotrophic community dominated by cyanobacteria and held together by slimy secretions produced by various microbial groups. When contaminated water containing high concentrations of metals is passed over microbial mats immobilized on glass wool, there is rapid removal of the metals from the water. The mats are tolerant of high concentrations of toxic metals and metalloids, such as cadmium, lead, chromium, selenium and arsenic (up to 350 mg L^–1). This tolerance may be due to a number of mechanisms at the molecular, cellular and community levels. Management of toxic metals by the mats is related to deposition of metal compounds outside the cell surfaces as well as chemical modification of the aqueous environment surrounding the mats. The location of metal deposition is determined by factors such as redox gradients, cell surface micro-environments and secretion of extra-cellular bioflocculents. Metal-binding flocculents (polyanionic polysaccharides) are produced in large quantities by the cyanobacterial component of the mat. Steep gradients of redox and oxygen exist from the surface through the laminated strata of microbes. These are produced by photosynthetic oxygen production at the surface and heterotrophic consumption in the deeper regions. Additionally, sulfur-reducing bacteria colonize the lower strata, removing and utilizing the reducing H₂S, rather than water, for photosynthesis. Thus, depending on the chemical character of the microzone of the mat, the sequestered metals or metalloids can be oxidized, reduced and precipitated as sulfides or oxides. For example precipitates of red amorphous elemental selenium were identified in mats exposed to selenate (Se-VI) and insoluble precipitates of manganese, chromium, cadmium, cobalt, and lead were found in mats exposed to soluble salts of these metals. Constructed microbial mats offer several advantages for use in the bioremediation of metal-contaminated sites. These include low cost, durability, ability to function in both fresh and salt water, tolerance to high concentrations of metals and metalloids and the unique capacity of mats to form associations with new microbial species. Thus one or several desired microbial species might be integrated into mats in order to design the community for specific bioremediation applications.     

From water to edible fish. Transfer of metals and metalloids in the San Roque Reservoir (Córdoba,Argentina). Implications associated with fish consumption

The concentration of Mn, Fe, Zn, Cu, Cd, Cr, Ni, Ag, Mo, Nd, Al, Ce, As, Sr, Pb, Pt and Hg was analysed in water, sediments, and aquatic organisms from the San Roque Reservoir (Córdoba-Argentina), sampled during the wet and dry season, to evaluate their transfer through the food web. Stable nitrogen (δ¹⁵N) isotopes were used to investigate trophic interactions. According to this, samples were divided into three trophic groups: plankton, shrimp (Palaemonetes argentinus) and fish (Silverside, Odontesthes bonariensis). Liver and gills are the main heavy metal storage tissues in fish. Hg and As concentrations in the muscle of O. bonariensis exceed the Oral Reference doses for metals established by USEPA (2009). Trophic magnification factors (TMFs) for each element were determined from the slope of the regression between trace element concentrations and δ¹⁵N. Calculated TMFs showed fundamental differences in the trophodynamics of the studied elements during the wet and dry season in the San Roque Reservoir. Concentrations of Ni, Cd, Cr, Al, Mn, Fe, Mo, Ce, Nd, Pt and Pb during both seasons, and Sr during the dry season, showed statistically significant decreases (TMF < 1) with increasing trophic levels. Thus these elements were trophically diluted in the San Roque food chain. Conversely, Cu, Ag and As (dry season) showed no significant relationships with trophic levels. Among the elements studied, Hg in the wet season, and Zn in the dry season were the only ones showing a statistically significant increase (TMF > 1) in concentration with trophic level. Current results trigger the need for further studies to establish differential behaviour with different species within the aquatic web, particularly when evaluating the transfer of toxic elements to edible organisms, which could pose health risks to humans.     

In situ analysis of metal(loid)s in plants: State of the art and artefacts

Metals and metalloids play important roles in plant function and metabolism. Likewise, plants subsequently introduce vital dietary nutrition to people and animals. Understanding the transport, localisation and speciation of these elements is critical for understanding availability and metabolic pathways. Subsequently this knowledge can be applied to plant physiology and agricultural research, food science and genetic engineering.This review focuses on the most recent status of in situ techniques to visualise spatial distributions and assess the speciation of metals and metalloids. The techniques addressed include: histochemical analysis, autoradiography, LA-ICP-MS, SIMS, SEM including EDX, PIXE; and synchrotron methods: XRF, differential and fluorescence tomography, and X-ray absorption techniques.This review has been written with the intent of plant researchers to gain familiarity with techniques to which they are not accustom but wish to extend their research with alternative, but complementary, capabilities. Importantly, the disadvantages as well as advantages, have been highlighted for each technique and potential artefacts induced by the analysis or sample preparation are reviewed. These often overlooked aspects are the points critical for novice use of unfamiliar techniques and are offered for advancing research approaches commensurate with the accelerating interest regarding metal(loid)s in botanical specimens.     

Association of whole blood metals/metalloids with severity in sepsis patients: A prospective,single-center,pilot study

BackgroundTrace metals/metalloids were important for the biological functions of both the eukaryotic host and the microorganism. Their concentrations and variations may associate with the critical illness in sepsis, which still needs to be investigated.MethodsWe performed a prospective cohort study on the patients with sepsis admitted to Tongji hospital (Wuhan, China) from Jul 01 to Dec 31, 2021. Sepsis was diagnosed in accordance with the third international consensus definitions for sepsis and septic shock (Sepsis-3). The concentrations of metals/metalloids including magnesium (Mg), calcium (Ca), chromium (Cr), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), mercury (Hg), thallium (Tl) and lead (Pb) in whole blood were analyzed by ICP-MS based methods.ResultsCompared to the healthy controls, patients with sepsis showed higher levels of Ca, Cr and Cu, and lower levels of Mg, Mn, Fe, Zn, As, Hg and Pb. Further analysis between the critical illness and noncritical illness, revealed the Mn, Fe were significantly lower in the critically-ill sepsis. The longitudinal profile of the two metals show the differences appeared to exist almost throughout the clinical course. By performing the binary regression logistic analysis, we determined the Fe, Mn as independently risk factors for critical illness in sepsis, with effect sizes (β) of 17.14 (95%CI: 1.79–163.81) and 10.83 (1.96–59.83), respectively, which collectively discriminated 83.3% of all cases between critical-illness and non-critically illness.ConclusionsThe variations of whole blood metals/metalloids were associated with the critically-ill sepsis.