Detecting Gold Biomineralization by Delftia acidovorans Biofilms on a Quartz Crystal Microbalance

© 2019 American Chemical Society. The extensive use of gold in sensing, diagnostics, and electronics has led to major concerns in solid waste management since gold and other heavy metals are nonbiodegradable and can easily accumulate in the environment. Moreover, gold ions are extremely reactive and potentially harmful for humans. Thus, there is an urgent need to develop reliable methodologies to detect and possibly neutralize ionic gold in aqueous solutions and industrial wastes. In this work, by using complementary measurement techniques such as quartz crystal microbalance (QCM), atomic force microscopy, crystal violet staining, and optical microscopy, we investigate a promising biologically induced gold biomineralization process accomplished by biofilms of bacterium Delftia acidovorans. When stressed by Au3+ ions, D. acidovorans is able to neutralize toxic soluble gold by excreting a nonribosomal peptide, which forms extracellular gold nanonuggets via complexation with metal ions. Specifically, QCM, a surface-sensitive transducer, is employed to quantify the production of these gold complexes directly on the D. acidovorans biofilm in real time. Detailed kinetics obtained by QCM captures the condition for maximized biomineralization yield and offers new insights underlying the biomineralization process. To the best of our knowledge, this is the first study providing an extensive characterization of the gold biomineralization process by a model bacterial biofilm. We also demonstrate QCM as a cheap, user-friendly sensing platform and alternative to standard analytical techniques for studies requiring high-resolution quantitative details, which offers promising opportunities in heavy-metal sensing, gold recovery, and industrial waste treatment

Urban mining of municipal solid waste incineration (MSWI) residues with emphasis on bioleaching technologies: a critical review

Metals are essential in our daily lives and have a finite supply, being simultaneously contaminants of concern. The current carbon emissions and environmental impact of mining are untenable. We need to reclaim metals sustainably from secondary resources, like waste. Biotechnology can be applied in metal recovery from waste streams like fly ashes and bottom ashes of municipal solid waste incineration (MSWI). They represent substantial substance flows, with roughly 46 million tons of MSWI ashes produced annually globally, equivalent in elemental richness to low-grade ores for metal recovery. Next-generation methods for resource recovery, as in particular bioleaching, give the opportunity to recover critical materials and metals, appropriately purified for noble applications, in waste treatment chains inspired by circular economy thinking. In this critical review, we can identify three main lines of discussion: (1) MSWI material characterization and related environmental issues; (2) currently available processes for recycling and metal recovery; and (3) microbially assisted processes for potential recycling and metal recovery. Research trends are chiefly oriented to the potential exploitation of bioprocesses in the industry. Biotechnology for resource recovery shows increasing effectiveness especially downstream the production chains, i.e., in the waste management sector. Therefore, this critical discussion will help assessing the industrial potential of biotechnology for urban mining of municipal, post-combustion waste

Cooling induces phase separation in membranes derived from isolated CNS myelin

Purified myelin membranes (PMMs) are the starting material for biochemical analyses such as the isolation of detergent-insoluble glycosphingolipid-rich domains (DIGs), which are believed to be representatives of functional lipid rafts. The normal DIGs isolation protocol involves the extraction of lipids under moderate cooling. Here, we thus address the influence of cooling on the structure of PMMs and its sub-fractions. Thermodynamic and structural aspects of periodic, multilamellar PMMs are examined between 4°C and 45°C and in various biologically relevant aqueous solutions. The phase behavior is investigated by small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). Complementary neutron diffraction (ND) experiments with solid-supported myelin multilayers confirm that the phase behavior is unaffected by planar confinement. SAXS and ND consistently show that multilamellar PMMs in pure water become heterogeneous when cooled by more than 10–15°C below physiological temperature, as during the DIGs isolation procedure. The heterogeneous state of PMMs is stabilized in physiological solution, where phase coexistence persists up to near the physiological temperature. This result supports the general view that membranes under physiological conditions are close to critical points for phase separation. In presence of elevated Ca2+ concentrations (> 10 mM), phase coexistence is found even far above physiological temperatures. The relative fractions of the two phases, and thus presumably also their compositions, are found to vary with temperature. Depending on the conditions, an “expanded” phase with larger lamellar period or a “compacted” phase with smaller lamellar period coexists with the native phase. Both expanded and compacted periods are also observed in DIGs under the respective conditions. The observed subtle temperature-dependence of the phase behavior of PMMs suggests that the composition of DIGs is sensitive to the details of the isolation protocol

An evolutionary approach to preference disaggregation in a MURAME-based credit scoring problem

In this paper we use an evolutionary approach in order to infer the values of the parameters (weights of criteria, preference, indifference and veto thresholds) for developing the multicriteria method MURAME. According to the logic of preference disaggregation, the problem consists in finding the parameters that minimize the inconsistency between the model obtained with those parameters and that one connected with a given reference set of decisions revealed by the decision maker; in particular, two kinds of functions are considered in this analysis, representing a measure of the model inconsistency compared to the actual preferential system. In order to find a numerical solution of the mathematical programming problem involved, we adopt an evolutionary algorithm based on the Particle Swarm Optimization (PSO) method, which is an iterative heuristics grounded on swarm intelligence. The proposed approach is finally applied to a creditworthiness evaluation problem in order to test the methodology on a real data set provided by an Italian bank

Effects of pollen collection on colony development and in the bromatological composition Apis mellifera L. pupae

Africanized bees (Apis mellifera L.) were studied in the Botucatu region (São Paulo State), Brazil, from August to November, 1996, with the objective of quantifying pollen trapping and its effects on colony development and composition of worker bee pupae. Mean trapped pollen yield was 1.47 kg/beehive. Trapping had little effect on brood production, causing only a 9.7% reduction in total worker brood area and a 4.0% reduction in drone brood area, as compared to the treatment without pollen types. Pollen harvest did not affect the bromatological composition of worker pupae (white bodies and slightly pigmented eyes), mean values obtained for both treatments being 18.87% dry matter, 48.07% crude protein, 18.52% ether extract and 3.72% ash

Bromatological and mineral compositions of collected pollen for africanized honeybees (Apis mellifera L.) in Botucatu, São Paulo State

The bromatological and mineral compositions of pollen collected by Africanized honeybees (Apis mellifera L.) in the Botucatu region, São Paulo State, Brazil, from August to November, 1966, were investigated. The pollen collections from six beehives, at weekly intervals, lasted for seven consecutive days. Mean fresh pollen composition was: 75.9% dry matter, 26.2% crude protein (CP), 5.1% ether extract (EE), 2.6% ash, 1.1% crude fiber, 3.58% nitrogen, 0.43% phosphorus, 0.67% potassium, 0.26% calcium, 0.08% magnesium, 0.21% sulfur, 114.2 ppm iron, 88.4 ppm zinc, 15.0 ppm copper, 32.4 ppm manganese, and 9.9 ppm boron. Statistical analysis showed that pollen collected in October had the highest contents of CP, and of the elements P, S and Mn compared to the other months. According to cluster and principal components analyses for bromatological composition, the variables with most and least discriminatory power were the percentages of CP and EE, respectively. As to mineral composition, the most discriminatory variables were S, Mn, and N, while the least discriminatory were Mg, B, and K

Rheology of the Electric Double Layer in Electrolyte Solutions

Electric double layers (EDLs) are ionic structures formed on charged surfaces and play an important role in various biological and industrial processes. An extensive study in the past decade has revealed the structure of the EDL in concentrated electrolyte solutions of both ordinary salts and ionic liquids. However, how the EDL structure affects their material properties remains a challenging topic due to technical difficulties of these measurements at nanoscale. In this work, we report the first detailed characterization of the viscoelasticity of the EDL formed over a wide range of ion concentrations, including concentrated electrolyte solutions. Specifically, we investigate the complex shear modulus of the EDL by measuring the resonant frequency and the energy dissipation of a quartz crystal microbalance (QCM), a surface-sensitive device, immersed in aqueous solutions containing three types of solutes: an ionic liquid, 1-butyl-3-methylimidazolium chloride (BmimCl); an ordinary salt, sodium chloride (NaCl); and a nonelectrolyte, ethylene glycol (EG). For the two electrolyte solutions, we observe a monotonic decrease in the resonant frequency and a monotonic increase in the energy dissipation with increasing ion concentrations due to the presence of the EDL. The complex shear modulus of the EDL is estimated through a wave propagation model in which the density and shear modulus of the EDL decay exponentially toward those of the bulk solution. Our results show that both the storage and the loss modulus of the EDL increase rapidly with increasing ion concentrations in the low ion concentration regime (<1 M) but reach saturation values with similar magnitude at a sufficiently high ion concentration. The shear viscosity of the EDL near the charged QCM surface is approximately 50 times for NaCl solutions and 500 times for BmimCl solutions of the bulk solution value at the saturation concentration. We also demonstrate that QCM can be utilized for analyzing the rheological properties of the EDL, thus providing a complementary, low-cost, and portable alternative to conventional laboratory instruments such as the surface force apparatus. Our results elucidate new perspectives on the viscoelastic properties of the EDL and can potentially guide device optimization for applications such as biosensing and fast charging of batteries