Evidence for autotrophic growth of purple sulfur bacteria using pyrite as electron and sulfur source.

Purple sulfur bacteria (PSB) are capable of anoxygenic photosynthesis via oxidizing reduced sulfur compounds and are considered key drivers of the sulfur cycle in a range of anoxic environments. In this study, we show that Allochromatium vinosum (a PSB species) is capable of autotrophic growth using pyrite as the electron and sulfur source. Comparative growth profile, substrate characterization, and transcriptomic sequencing data provided valuable insight into the molecular mechanisms underlying the bacterial utilization of pyrite and autotrophic growth. Specifically, the pyrite-supported cell cultures ("py"') demonstrated robust but much slower growth rates and distinct patterns from their sodium sulfide-amended positive controls. Up to ~200-fold upregulation of genes encoding various c- and b-type cytochromes was observed in "py," pointing to the high relevance of these molecules in scavenging and relaying electrons from pyrite to cytoplasmic metabolisms. Conversely, extensive downregulation of genes related to LH and RC complex components indicates that the electron source may have direct control over the bacterial cells' photosynthetic activity. In terms of sulfur metabolism, genes encoding periplasmic or membrane-bound proteins (e.g., FccAB and SoxYZ) were largely upregulated, whereas those encoding cytoplasmic proteins (e.g., Dsr and Apr groups) are extensively suppressed. Other notable differentially expressed genes are related to flagella/fimbriae/pilin(+), metal efflux(+), ferrienterochelin(-), and [NiFe] hydrogenases(+). Characterization of the biologically reacted pyrite indicates the presence of polymeric sulfur. These results have, for the first time, put the interplay of PSB and transition metal sulfide chemistry under the spotlight, with the potential to advance multiple fields, including metal and sulfur biogeochemistry, bacterial extracellular electron transfer, and artificial photosynthesis. IMPORTANCE: Microbial utilization of solid-phase substrates constitutes a critical area of focus in environmental microbiology, offering valuable insights into microbial metabolic processes and adaptability. Recent advancements in this field have profoundly deepened our knowledge of microbial physiology pertinent to these scenarios and spurred innovations in biosynthesis and energy production. Furthermore, research into interactions between microbes and solid-phase substrates has directly linked microbial activities to the surrounding mineralogical environments, thereby enhancing our understanding of the relevant biogeochemical cycles. Our study represents a significant step forward in this field by demonstrating, for the first time, the autotrophic growth of purple sulfur bacteria using insoluble pyrite (FeS2) as both the electron and sulfur source. The presented comparative growth profiles, substrate characterizations, and transcriptomic sequencing data shed light on the relationships between electron donor types, photosynthetic reaction center activities, and potential extracellular electron transfer in these organisms capable of anoxygenic photosynthesis. Furthermore, the findings of our study may provide new insights into early-Earth biogeochemical evolutions, offering valuable constraints for understanding the environmental conditions and microbial processes that shaped our planet's history.

Aerosol microdroplets exhibit a stable pH gradient.

Suspended aqueous aerosol droplets (<50 µm) are microreactors for many important atmospheric reactions. In droplets and other aquatic environments, pH is arguably the key parameter dictating chemical and biological processes. The nature of the droplet air/water interface has the potential to significantly alter droplet pH relative to bulk water. Historically, it has been challenging to measure the pH of individual droplets because of their inaccessibility to conventional pH probes. In this study, we scanned droplets containing 4-mercaptobenzoic acid-functionalized gold nanoparticle pH nanoprobes by 2D and 3D laser confocal Raman microscopy. Using surface-enhanced Raman scattering, we acquired the pH distribution inside approximately 20-µm-diameter phosphate-buffered aerosol droplets and found that the pH in the core of a droplet is higher than that of bulk solution by up to 3.6 pH units. This finding suggests the accumulation of protons at the air/water interface and is consistent with recent thermodynamic model results. The existence of this pH shift was corroborated by the observation that a catalytic reaction that occurs only under basic conditions (i.e., dimerization of 4-aminothiophenol to produce dimercaptoazobenzene) occurs within the high pH core of a droplet, but not in bulk solution. Our nanoparticle probe enables pH quantification through the cross-section of an aerosol droplet, revealing a spatial gradient that has implications for acid-base-catalyzed atmospheric chemistry.

Bromide ion-functionalized nanoprobes for sensitive and reliable pH measurement by surface-enhanced Raman spectroscopy.

4-Mercaptopyridine (4-Mpy) is a pH reporter molecule commonly used to functionalize nanoprobes for surface-enhanced Raman spectroscopy (SERS) based pH measurements. However, nanoprobes functionalized by 4-Mpy alone have low pH sensitivity and are subject to interference by halide ions in sample media. To improve nanoprobe pH sensitivity and reliability, we functionalized gold nanoparticles (AuNPs) with both 4-Mpy and bromide ion (Br-). Br- electrostatically stabilizes protonated 4-Mpy, thus enabling sensitive SERS detection of the protonation state of 4-Mpy as a function of pH while also reducing variability caused by external halide ions. Through optimization of the functionalization parameters, including suspension pH, [4-Mpy], and [Br-], the developed nanoprobes enable monitoring of pH from 2.1 to 10 with high SERS activity and minimal interference from halide ions within the sample matrix. As a proof of concept, we were able to track nanoprobe location and image the pH distribution inside individual cancer cells. This study provides a novel way to engineer reliable 4-Mpy-functionalized SERS nanoprobes for the sensitive analysis of spatially localized pH features in halide ion-containing microenvironments.

Real-Time Monitoring of Ligand Exchange Kinetics on Gold Nanoparticle Surfaces Enabled by Hot Spot-Normalized Surface-Enhanced Raman Scattering.

Nanoparticle surface coatings dictate their fate, transport, and bioavailability. We used a gold nanoparticle-bacterial cellulose substrate and "hot spot"-normalized surface-enhanced Raman scattering (HSNSERS) to achieve in situ and real-time monitoring of ligand exchange reactions on the gold surface. This approach enables semiquantitative determination of citrate surface coverage. Following exposure of the citrate-coated nanoparticles to a suite of guest ligands (thiolates, amines, carboxylates, inorganic ions, and proteins), the guest ligand signal exhibited first-order growth kinetics, while the desorption mediated decay of the citrate signal followed a first-order model. Guest ligand functional group chemistry dictated the kinetics of citrate desorption, while the guest ligand concentration played only a minor role. Thiolates and BSA were more efficient at ligand exchange than amine-containing chemicals, carboxylate-containing chemicals, and inorganic salts due to their higher binding energies with the AuNP surface. Amine-containing molecules overcoated rather than displaced the citrate layer via electrostatic interaction. Citrate exhibited low resistance to replacement at high surface coverages, but higher resistance at lower coverage, thus suggesting a transformation of the citrate-binding mode during desorption. High resistance to replacement in streamwater suggests that the role of surface-adsorbed citrate in nanomaterial fate and transport must be better understood.

Improved Quantitative SERS Enabled by Surface Plasmon Enhanced Elastic Light Scattering.

The application of surface-enhanced Raman spectroscopy (SERS) for everyday quantitative analysis is hindered by the point-to-point variability of SERS substrates that arises due to the heterogeneous distribution of localized electromagnetic fields across a suite of plasmonic nanostructures. Herein, we adopt surface-enhanced elastic scattering as a SERS internal standard. Both elastic and inelastic (i.e., Raman) scattering are simultaneously enhanced by a given "hot spot", and thus, the surface-enhanced elastic scattering signal provides a localized intrinsic internal standard that scales across all of the plasmon-enhanced electromagnetic fields within a substrate. Elastically scattered light originates from the amplified spontaneous emission (ASE) of the commercial laser, leading to the formation of a low-wavenumber pseudo band that arises from the interaction of the ASE and the edge filter. A theoretical model was developed to illustrate the underlying mechanism supporting this normalization approach. The normalized Raman signals are independent of the incident laser intensity and the density of "hot spots" for numerous SERS substrates. Following "hot-spot" (HS) normalization, the coefficient of variation for the tested SERS substrates decreases from 10 to 60% to 2%-7%. This approach significantly improves SERS quantitation of four chloroanilines and enables collection of highly reproducible analyte adsorption results under both static and dynamic imaging conditions. Overall, this approach provides a simple means to improve SERS reproducibility without the need to use additional chemicals as internal standards.

Surface-Enhanced Raman Spectroscopy Characterization of Salt-Induced Aggregation of Gold Nanoparticles.

Low-frequency (<300 cm-1 ) vibrational interactions between gold surfaces and dissolved halides in water were investigated by surface-enhanced Raman spectroscopy (SERS). Experiments with NaF, NaCl, NaBr, and NaI salts indicate that the Raman shifts of the Au-X- SERS bands correlate with the bond strength of the corresponding covalent interaction. These low-frequency SERS bands open up new means to investigate the aggregation of nanoparticles in aqueous environments.

Controlled Evaluation of the Impacts of Surface Coatings on Silver Nanoparticle Dissolution Rates.

Silver nanoparticles (AgNPs) are increasingly being incorporated into a range of consumer products and as such there is significant potential for the environmental release of either the AgNPs themselves or Ag+ ions. When AgNPs are exposed to environmental systems, the engineered surface coating can potentially be displaced or covered by naturally abundant macromolecules. These capping agents, either engineered or incidental, potentially block reactants from surface sites and can alter nanoparticle transformation rates. We studied how surface functionalization affects the dissolution of uniform arrays of AgNPs fabricated by nanosphere lithography (NSL). Bovine serum albumin (BSA) and two molecular weights of thiolated polyethylene glycol (PEG; 1000 and 5000 Da) were tested as model capping agents. Dissolution experiments were conducted in air-saturated phosphate buffer containing 550 mM NaCl. Tapping-mode atomic force microscopy (AFM) was used to measure changes in AgNP height over time. The measured dissolution rate for unfunctionalized AgNPs was 1.69 ± 0.23 nm/d, while the dissolution rates for BSA, PEG1000, and PEG5000 functionalized samples were 0.39 ± 0.05, 0.20 ± 0.10, and 0.14 ± 0.07 nm/d, respectively. PEG provides a steric barrier restricting mass transfer of reactants to sites on the AgNP surface and thus diminishes the dissolution rate. The effects of BSA, however, are more complicated with BSA initially enhancing dissolution, but providing protection against dissolution over extended time.

Aerosol Emissions from Fuse-Deposition Modeling 3D Printers in a Chamber and in Real Indoor Environments.

Three-dimensional (3D) printers are known to emit aerosols, but questions remain about their composition and the fundamental processes driving emissions. The objective of this work was to characterize the aerosol emissions from the operation of a fuse-deposition modeling 3D printer. We modeled the time- and size-resolved emissions of submicrometer aerosols from the printer in a chamber study, gained insight into the chemical composition of emitted aerosols using Raman spectroscopy, and measured the potential for exposure to the aerosols generated by 3D printers under real-use conditions in a variety of indoor environments. The average aerosol emission rates ranged from ∼108 to ∼1011 particles min-1, and the rates varied over the course of a print job. Acrylonitrile butadiene styrene (ABS) filaments generated the largest number of aerosols, and wood-infused polylactic acid (PLA) filaments generated the smallest amount. The emission factors ranged from 6 × 108 to 6 × 1011 per gram of printed part, depending on the type of filament used. For ABS, the Raman spectra of the filament and the printed part were indistinguishable, while the aerosol spectra lacked important peaks corresponding to styrene and acrylonitrile, which are both present in ABS. This observation suggests that aerosols are not a result of volatilization and subsequent nucleation of ABS or direct release of ABS aerosols.

Adsorption of Phthalates on Impervious Indoor Surfaces.

Sorption of semivolatile organic compounds (SVOCs) onto interior surfaces, often referred to as the "sink effect", and their subsequent re-emission significantly affect the fate and transport of indoor SVOCs and the resulting human exposure. Unfortunately, experimental challenges and the large number of SVOC/surface combinations have impeded progress in understanding sorption of SVOCs on indoor surfaces. An experimental approach based on a diffusion model was thus developed to determine the surface/air partition coefficient K of di-2-ethylhexyl phthalate (DEHP) on typical impervious surfaces including aluminum, steel, glass, and acrylic. The results indicate that surface roughness plays an important role in the adsorption process. Although larger data sets are needed, the ability to predict K could be greatly improved by establishing the nature of the relationship between surface roughness and K for clean indoor surfaces. Furthermore, different surfaces exhibit nearly identical K values after being exposed to kitchen grime with values that are close to those reported for the octanol/air partition coefficient. This strongly supports the idea that interactions between gas-phase DEHP and soiled surfaces have been reduced to interactions with an organic film. Collectively, the results provide an improved understanding of equilibrium partitioning of SVOCs on impervious surfaces.

Stable oligonucleotide-functionalized gold nanosensors for environmental biocontaminant monitoring.

The global propagation of environmental biocontaminants such as antibiotic resistant pathogens and their antibiotic resistance genes (ARGs) is a public health concern that highlights the need for improved monitoring strategies. Here, we demonstrate the environmental stability and applicability of an oligonucleotide-functionalized gold nanosensor. The mecA ARG was targeted as model biocontaminant due to its presence in clinically-relevant pathogens and to its emergence as an environmental contaminant. mecA-specific nanosensors were tested for antibiotic resistance gene (ARG) detection in ARG-spiked effluent from four wastewater treatment plants (WWTPs). The mecA-specific nanosensors showed stability in environmental conditions and in high ionic strength ([MgCl2]<50mM), and high selectivity against mismatched targets. Spectrophotometric detection was reproducible with an LOD of 70pM (≈4×107genes/µL), even in the presence of interferences associated with non-target genomic DNA and complex WWTP effluent. This contribution supports the environmental applicability of a new line of cost-effective, field-deployable tools needed for wide-scale biocontaminant monitoring.

Preparation and evaluation of nanocellulose-gold nanoparticle nanocomposites for SERS applications.

Nanocellulose is of research interest due to its extraordinary optical, thermal, and mechanical properties. The incorporation of guest nanoparticles into nanocellulose substrates enables production of novel nanocomposites with a broad range of applications. In this study, gold nanoparticle/bacterial cellulose (AuNP/BC) nanocomposites were prepared and evaluated for their applicability as surface-enhanced Raman scattering (SERS) substrates. The nanocomposites were prepared by citrate mediated in situ reduction of Au(3+) in the presence of a BC hydrogel at 303 K. Both the size and morphology of the AuNPs were functions of the HAuCl4 and citrate concentrations. At high HAuCl4 concentrations, Au nanoplates form within the nanocomposites and are responsible for high SERS enhancements. At lower HAuCl4 concentrations, uniform nanospheres form and the SERS enhancement is dependent on the nanosphere size. The time-resolved increase in the SERS signal was probed as a function of drying time with SERS 'hot-spots' primarily forming in the final minutes of nanocomposite drying. The application of the AuNP/BC nanocomposites for detection of the SERS active dyes MGITC and R6G as well as the environmental contaminant atrazine is illustrated as is its use under low and high pH conditions. The results indicate the broad applicability of this nanocomposite for analyte detection.

MGITC facilitated formation of AuNP multimers.

Malachite green isothiocyanate (MGITC) is frequently used as a surface bound Raman reporter for metal nanoparticle-enabled surface enhanced Raman scattering (SERS). To date, however, no study has focused on the application of MGITC for the formation of stable "hot-spot" aggregates for Raman imaging applications. Herein we report a method to produce a series of suspensions of MGITC functionalized gold nanoparticles (MGITC-AuNPs) that at one extreme consist primarily of monomers and at the other extreme as mixtures of multimers and monomers. Monomer and multimer morphologies were characterized by scanning electron microscopy and atomic force microscopy using a reliable spin-coating deposition sampling method. The multimers generally include 2, 3, or 4 individual AuNPs with an average number of 3 ± 1. The number of multimers produced in a given suspension was found to be dependent on the volume and concentration of MGITC initially applied. The surface binding of MGITC to both monomeric and multimeric MGITC-AuNPs was investigated by Raman and SERS, and the degree of aggregation in the multimer suspension was evaluated based upon the measured variation of the MGITC SERS intensity of the AuNPs. Using an estimated extinction coefficient of 1.22 ± 0.41 × 10(11) M(-1) cm(-1) at ≈850 nm for the localized surface plasmon resonance (LSPR) band of the MGITC-AuNP multimers, the multimer concentrations were calculated by Beer's Law.

Nanoclustered gold honeycombs for surface-enhanced Raman scattering.

A honeycomb-shaped gold substrate was developed for surface-enhanced Raman imaging (SERI). The honeycombs are composed of clusters of 50-70 nm gold nanoparticles and exhibit high Raman enhancement efficiency. An average surface enhancement factor (ASEF) of 1.7 × 10(6) was estimated for a monolayer of L-cysteine molecules adsorbed to gold via a thiol linkage. The presence of a linear relationship in the low concentration region was observed in SERI detection of malachite green isothiocyanate (MGITC). These results together with the high reproducibility and simple and cost-effective fabrication of this substrate suggest that it has utility for applications of surface-enhanced Raman scattering (SERS) in quantitative diagnoses and analyte detection.

Differentiation of microcystin, nodularin, and their component amino acids by drop-coating deposition Raman spectroscopy.

Raman spectra of microcystin-LR (MC-LR), MC-RR, MC-LA, MC-LF, MC-LY, MC-LW, MC-YR, and nodularin collected by drop-coating deposition Raman (DCDR) spectroscopy are sufficiently unique for variant identification. Amino acid spectra of L-phenylalanine, L-leucine, L-alanine, D-alanine, L-glutamic acid, L-arginine, L-tryptophan, L-tyrosine, and N-methyl-D-aspartic acid were collected in crystalline, DCDR, and aqueous forms to aid in cyanotoxin Raman peak assignments. Both peak ratio analysis and principal component analysis (PCA) properly classified 72 DCDR spectra belonging to the eight toxins. Loading plots for the first three principal components (PCs) most heavily weighted the peaks highlighted in the peak ratio analysis, specifically the 760 cm(-1) tryptophan peak, 853 cm(-1) tyrosine peak, and 1006 cm(-1) phenylalanine peak. Peak ratio analyses may be preferred under some circumstances because of the ease and speed with which the ratios can be computed, even by untrained lab technicians. A set of rules was created to mathematically classify toxins using the peak ratios. DCDR methods hold great potential for future application in routine monitoring because portable and hand-held Raman spectrometers are commercially available, DCDR spectra can be collected in seconds for biomolecule mixtures as well as samples containing impurities, and the method requires far fewer consumables than conventional cyanotoxin detection methods.

Solvent effects on resonance Raman and hyper-Raman scatterings for a centrosymmetric distyrylbenzene and relationship to two-photon absorption.

Resonance Raman (RR) and resonance hyper-Raman (RHR) spectra have been obtained for a nominally centrosymmetric dialkylammonium-substituted distyrylbenzene that was previously shown to exhibit a strong solvent polarity effect on its two-photon absorption strength. Spectra have been obtained in acetonitrile, methanol, dimethylsulfoxide, and water. In each solvent, the RR and RHR spectra show very similar intensity patterns in the strongest lines in both the C=C and C-C stretching regions, but the RHR peaks are shifted to higher energies by 5-10 cm(-1). These are interpreted as vibrations of similar mode character but different symmetries, with u symmetry modes observed in RHR and g symmetry modes in RR. In all solvents the nonzero chromophore contribution to the hyper-Rayleigh scattering indicates that the center of symmetry is broken to some degree, and this effect is more pronounced in water than in the other three solvents. The ratio of RR intensity to one-photon fluorescence intensity shows an approximate inverse relationship with the fluorescence quantum yield, consistent with the approximate solvent independence of the one-photon transition strength implied by the linear absorption spectra. The ratio of RHR intensity to two-photon fluorescence intensity is smaller than the corresponding RR to one-photon fluorescence ratio in all four solvents.

Pulmonary Exposure to Magnéli Phase Titanium Suboxides Results in Significant Macrophage Abnormalities and Decreased Lung Function.

Coal is one of the most abundant and economic sources for global energy production. However, the burning of coal is widely recognized as a significant contributor to atmospheric particulate matter linked to deleterious respiratory impacts. Recently, we have discovered that burning coal generates large quantities of otherwise rare Magnéli phase titanium suboxides from TiO2 minerals naturally present in coal. These nanoscale Magnéli phases are biologically active without photostimulation and toxic to airway epithelial cells in vitro and to zebrafish in vivo. Here, we sought to determine the clinical and physiological impact of pulmonary exposure to Magnéli phases using mice as mammalian model organisms. Mice were exposed to the most frequently found Magnéli phases, Ti6O11, at 100 parts per million (ppm) via intratracheal administration. Local and systemic titanium concentrations, lung pathology, and changes in airway mechanics were assessed. Additional mechanistic studies were conducted with primary bone marrow derived macrophages. Our results indicate that macrophages are the cell type most impacted by exposure to these nanoscale particles. Following phagocytosis, macrophages fail to properly eliminate Magnéli phases, resulting in increased oxidative stress, mitochondrial dysfunction, and ultimately apoptosis. In the lungs, these nanoparticles become concentrated in macrophages, resulting in a feedback loop of reactive oxygen species production, cell death, and the initiation of gene expression profiles consistent with lung injury within 6 weeks of exposure. Chronic exposure and accumulation of Magnéli phases ultimately results in significantly reduced lung function impacting airway resistance, compliance, and elastance. Together, these studies demonstrate that Magnéli phases are toxic in the mammalian airway and are likely a significant nanoscale environmental pollutant, especially in geographic regions where coal combustion is a major contributor to atmospheric particulate matter.

Resonance hyper-Raman spectra of zinc phthalocyanine.

Hyper-Raman spectra were obtained for zinc phthalocyanine in a dilute pyridine solution at excitation wavelengths that are two-photon resonant with the one-photon-allowed B band (360-380 nm) as well as with the two-photon absorption near 440 nm reported by Drobizhev et al. ( J. Chem. Phys. 2006, 124, 224701 ). In both regions, the hyper-Raman spectra were very different from the linear resonance Raman spectra at the corresponding excitation frequencies. While the resonance Raman spectra show only g symmetry modes, almost all of the hyper-Raman frequencies can be assigned as fundamentals of E u symmetry that also are observed in the infrared absorption spectrum or E u symmetry combination bands. These results contrast sharply with previous observations of highly noncentrosymmetric push-pull conjugated molecules and are consistent with a structure for phthalocyanine in solution that is centrosymmetric or nearly so. The hyper-Raman spectra show different intensity patterns in the two excitation regions, consistent with different Franck-Condon and/or vibronic coupling matrix elements for the different resonant states.

Protein-aided formation of triangular silver nanoprisms with enhanced SERS performance.

In this work, we present a modified seed-mediated synthetic strategy for the growth of silver nanoprisms with low shape polydispersity, narrow size distribution and tailored plasmonic absorbance. During the seed nucleation step, consensus sequence tetratricopeptide repeat (CTPR) proteins are utilized as potent stabilizers to facilitate the formation of planar-twinned Ag seeds. Ag nanoprisms were produced in high yield in a growth solution containing ascorbic acid and CTPR-stabilized Ag seeds. From the time-course UV-Vis and transmission electron microscopy (TEM) studies, we postulate that the growth mechanism is the combination of facet selective lateral growth and thermodynamically driven Ostwald ripening. The resultant Ag nanotriangles (NTs) exhibit excellent surface enhanced Raman spectroscopy (SERS) performance. The enhancement factor (EF) measured for the 4-mercapto benzoic acid (4-MBA) reporter is estimated to be 3.37 × 105 in solution and 2.8 × 106 for the SERS substrate.