Picocyanobacteria and deep-ocean fluorescent dissolved organic matter share similar optical properties

Marine chromophoric dissolved organic matter (CDOM) and its related fluorescent components (FDOM), which are widely distributed but highly photobleached in the surface ocean, are critical in regulating light attenuation in the ocean. However, the origins of marine FDOM are still under investigation. Here we show that cultured picocyanobacteria, Synechococcus and Prochlorococcus, release FDOM that closely match the typical fluorescent signals found in oceanic environments. Picocyanobacterial FDOM also shows comparable apparent fluorescent quantum yields and undergoes similar photo-degradation behaviour when compared with deep-ocean FDOM, further strengthening the similarity between them. Ultrahigh-resolution mass spectrometry (MS) and nuclear magnetic resonance spectroscopy reveal abundant nitrogen-containing compounds in Synechococcus DOM, which may originate from degradation products of the fluorescent phycobilin pigments. Given the importance of picocyanobacteria in the global carbon cycle, our results indicate that picocyanobacteria are likely to be important sources of marine autochthonous FDOM, which may accumulate in the deep ocean

Does case misclassification threaten the validity of studies investigating the relationship between neck manipulation and vertebral artery dissection stroke? No

Background: The purported relationship between cervical manipulative therapy (CMT) and stroke related to vertebral artery dissection (VAD) has been debated for several decades. A large number of publications, from case reports to case–control studies, have investigated this relationship. A recent article suggested that case misclassification in the case–control studies on this topic resulted in biased odds ratios in those studies. Discussion: Given its rarity, the best epidemiologic research design for investigating the relationship between CMT and VAD is the case–control study. The addition of a case-crossover aspect further strengthens the scientific rigor of such studies by reducing bias. The most recent studies investigating the relationship between CMT and VAD indicate that the relationship is not causal. In fact, a comparable relationship between vertebral artery-related stroke and visits to a primary care physician has been observed. The statistical association between visits to chiropractors and VAD can best be explained as resulting from a patient with early manifestation of VAD (neck pain with or without headache) seeking the services of a chiropractor for relief of this pain. Sometime after the visit the patient experiences VAD-related stroke that would have occurred regardless of the care received. This explanation has been challenged by a recent article putting forth the argument that case misclassification is likely to have biased the odds ratios of the case–control studies that have investigated the association between CMT and vertebral artery related stroke. The challenge particularly focused on one of the case–control studies, which had concluded that the association between CMT and vertebral artery related stroke was not causal. It was suggested by the authors of the recent article that misclassification led to an underestimation of risk. We argue that the information presented in that article does not support the authors’ claim for a variety of reasons, including the fact that the assumptions upon which their analysis is based lack substantiation and the fact that any possible misclassification would not have changed the conclusion of the study in question. Conclusion: Current evidence does not support the notion that misclassification threatens the validity of recent case–control studies investigating the relationship between CMT and VAD. Hence, the recent re-analysis cannot refute the conclusion from previous studies that CMT is not a cause of VAD.https://doi.org/10.1186/s12998-016-0124-

Photochemistry of Dissolved Organic Matter: Reactivity and application in constructed treatment wetlands

Constructed wetlands have the potential to provide low-energy treatment of pharmaceuticals and other micropollutants via photolysis. Natural dissolved organic matter (DOM) reacts with sunlight to produce reactive species such as singlet oxygen and excited triplet states of DOM that react quickly and efficiently with contaminants. To study the photo-chemistry of DOM, a unique solar-simulation system was developed, allowing for semi-continuous monitoring of absorbance and fluorescence spectra throughout the irradiation. This system was utilized to investigate the effect of solution pH on the fluorescence properties and degradation of DOM. For the first time, parallel factor (PARAFAC) analysis was utilized to deconvolute photo-labile, photo-stable, and pH- dependent fluorescent components during irradiation. Fluorescence is highly pH dependent, and as pH increases, the total amount of fluorescence loss, and the rate at which it is lost, increases significantly. This has important implications in treatment systems, as the photo-reactivity of DOM will change when pH gradients or fluctuations are observed. The photo-degradation of organic matter collected from a depth profile (0-4,500 m) the Sargasso Sea showed increased reactivity with increasing depth. Ultra-high resolution mass spectrometry (FT-MS) was used to characterize the samples, and correlation analyses between the fluorescence data and mass spectra revealed that high molecular weight, aromatic, and possibly polyphenolic compounds are contributing the most to the fluorescence properties that show the most reactivity in marine samples.Production of singlet oxygen, hydroxyl radical, and triplet excited states of DOM along two riverine transects in the Everglades were measured. The abundance of fluorescence PARAFAC components was compared to the reactive species production, and suggested that terrestrial organic matter may be more efficient producers of reactive species than microbial- or seagrass- derived organic matter. Finally, the relationship between optical properties of DOM samples collected around the world and their reactivity were investigated. Photo-irradiations and pH titrations were performed on all samples, and mass spectra collected via FT-MS. Humification indices, the biological index (BIX), and spectral slope from 275-295 nm were found to be most closely tied to changes in the mass spectra of the samples, and showed strong relationship to DOM source

Photo-Reactivity of Natural Dissolved Organic Matter from Fresh to Marine Waters in the Florida Everglades, USA

Natural dissolved organic matter (DOM) is the major absorber of sunlight in most natural waters and a critical component of carbon cycling in aquatic systems. The combined effect of light absorbance properties and related photo-production of reactive species are essential in determining the reactivity of DOM. Optical properties and in particular excitation–emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) have been used increasingly to track sources and fate of DOM. Here we describe studies conducted in water from two estuarine systems in the Florida Everglades, with a salinity gradient of 2 to 37 and dissolved organic carbon concentrations from 19.3 to 5.74 mg C L−1, aimed at assessing how the quantity and quality of DOM is coupled to the formation rates and steady-state concentrations of reactive species including singlet oxygen, hydroxyl radical, and the triplet excited state of DOM. These species were related to optical properties and PARAFAC components of the DOM. The formation rate and steady-state concentration of the carbonate radical was calculated in all samples. The data suggests that formation rates, particularly for singlet oxygen and hydroxyl radicals, are strongly coupled to the abundance of terrestrial humic-like substances. A decrease in singlet oxygen, hydroxyl radical, and carbonate radical formation rates and steady-state concentration along the estuarine salinity gradient was observed as the relative concentration of terrestrial humic-like DOM decreased due to mixing with microbial humic-like and protein-like DOM components, while the formation rate of triplet excited-state DOM did not change. Fluorescent DOM was also found to be more tightly coupled to reactive species generation than chromophoric DOM

Photochemistry illuminates ubiquitous organic matter fluorescence spectra

Dissolved organic matter (DOM) in aquatic environments forms a vast reservoir of carbon present as a complex supermixture of compounds. An efficient approach to tracking the production and removal of specific DOM fractions is needed across disciplines, for purposes that range from improving global carbon budgets to optimizing water treatment in engineered systems. Although widely used to study DOM, fluorescence spectroscopy has yet to deliver specific fractions with known spectral properties and predictable distributions. Here, we mathematically isolate four visible-wavelength fluorescent fractions in samples from contrasting lake, river, and ocean environments. Using parallel factor analysis (PARAFAC), we show that most measured fluorescence in environmental samples can be explained by ubiquitous spectra with nearly stable optical properties and photodegradation behaviors over environmental pH gradients. Sample extraction changed bulk fluorescence spectra but not the number or shape of underlying PARAFAC components, while photobleaching preferentially removed the two longest-wavelength components. New approaches to analyzing fluorescence data sets incorporating these findings should improve the interpretation of DOM fluorescence and increase its utility for tracing organic matter biogeochemistry in aquatic systems

PARAFAC Modeling of Irradiation- and Oxidation-Induced Changes in Fluorescent Dissolved Organic Matter Extracted from Poultry Litter

Parallel factor analysis (PARAFAC) applied to fluorescence excitation emission matrices (EEMs) allows quantitative assessment of the composition of fluorescent dissolved organic matter (DOM). In this study, we fit a four-component EEM-PARAFAC model to characterize DOM extracted from poultry litter. The data set included fluorescence EEMs from 291 untreated, irradiated (253.7 nm, 310–410 nm), and oxidized (UV–H₂O₂, ozone) poultry litter extracts. The four components were identified as microbial humic-, terrestrial humic-, tyrosine-, and tryptophan-like fluorescent signatures. The Tucker’s congruence coefficients for components from the global (i.e., aggregated sample set) model and local (i.e., single poultry litter source) models were greater than 0.99, suggesting that the global EEM-PARAFAC model may be suitable to study poultry litter DOM from individual sources. In general, the transformation trends of the four fluorescence components were comparable for all poultry litter sources tested. For irradiation at 253.7 nm, ozonation, and UV–H₂O₂ advanced oxidation, transformation of the humic-like components was slower than that of the tryptophan-like component. The opposite trend was observed for irradiation at 310–410 nm, due to differences in UV absorbance properties of components. Compared to the other EEM-PARAFAC components, the tyrosine-like component was fairly recalcitrant in irradiation and oxidation processes. This novel application of EEM-PARAFAC modeling provides insight into the composition and fate of agricultural DOM in natural and engineered systems

Effect of Photolysis on Absorption and Fluorescence Spectra of Light-Absorbing Secondary Organic Aerosols

Excitation–emission matrices (EEMs) constructed from fluorescence measurements are increasingly used for the characterization of chromophoric dissolved organic matter (CDOM) and light-absorbing atmospheric organic aerosols known as brown carbon (BrC). There is a high uncertainty in the effect of BrC aerosols on climate because their optical properties depend on the amount of time they spent in the atmosphere. In order to aid in the quantification of BrC aerosols’ contribution to radiative forcing, we investigated the effect of solar radiation on the fluorescence, expressed as EEMs, and absorption spectra of the water-soluble fraction of BrC species formed by the high-NOx photooxidation of benzene, toluene, p-xylene, and naphthalene. The BrC samples were prepared in a smog chamber, extracted in water, and irradiated in a solar simulator at a fixed pH of 3, representative of aerosol liquid water, or at a fixed pH of 6, representative of cloudwater. Semicontinuous fluorescence and absorbance measurements were carried out during the irradiation at 20 min intervals for 44 h. The absorption coefficients depended on the solution pH, with the solutions at pH 6 absorbing stronger than solutions at pH 3. All samples underwent a decrease in absorption coefficient at all visible wavelengths, whereas fluorescence intensities showed both increases and decreases in different regions of the EEMs. Upon comparison with CDOM samples, the fluorescence intensity of all secondary organic aerosol (SOA) samples decreased in the region of the EEMs where the characteristic terrestrial humic-like C peak occurs. These experimental observations suggest that (i) this type of BrC will have different effects on climate depending on whether it ends up in an acidic or neutral environment; (ii) exposure to UV radiation will diminish the ability of this type of BrC to affect climate on a time scale of about a day; (iii) fluorescence by BrC compounds has a minimal effect on aerosol radiative forcing; (iv) photooxidized aromatics may be closely related, in terms of optical properties, to CDOM found in fresh waters

Depth-dependent photodegradation of marine dissolved organic matter

Marine dissolved organic matter (DOM) in surface and deep waters of the eastern Atlantic Ocean and Sargasso Sea was analyzed by excitation emission matrix (EEM) fluorescence spectroscopy and parallel factor analysis (PARAFAC). Photo-degradation with semi-continuous monitoring of EEMs and absorbance spectra was used to measure the photo-degradation kinetics and changes of the PARAFAC components in a depth profile of DOM at the Bermuda Atlantic Time Series (BATS) station in the Sargasso Sea. A five component model was fit to the EEMs, which included traditional terrestrial-like, marine-like, and protein-like components. Terrestrial-like components showed the expected high photo-reactivity, but surprisingly, the traditional marine-like peak showed slight photo-production in surface waters, which may account for its prevalence in marine systems. Surface waters were depleted in photo-labile components while protein-like fluorescent components were enriched, consistent with previous studies. Ultra-high resolution mass spectrometry detected unique aliphatic compounds in the surface waters at the BATS site, which may be photo-produced or photo-stable. Principle component and canonical analysis showed strong correlations between relative contributions of unsaturated/aromatic molecular formulas and depth, with aliphatic compounds more prevalent in surface waters and aromatic compounds in deep waters. Strong correlations were seen between these aromatic compounds and humic-like fluorescent components. The rapid photo-degradation of the deep-sea fluorescent DOM in addition to the surface water relative depletion of aromatic compounds suggests that deep-sea fluorescent DOM may be too photochemically labile to survive during overturning circulation

Depth-dependent Photodegradation of Marine Dissolved Organic Matter

Marine dissolved organic matter (DOM) in surface and deep waters of the eastern Atlantic Ocean and Sargasso Sea was analyzed by excitation emission matrix (EEM) fluorescence spectroscopy and parallel factor analysis (PARAFAC). Photo-degradation with semi-continuous monitoring of EEMs and absorbance spectra was used to measure the photo-degradation kinetics and changes of the PARAFAC components in a depth profile of DOM at the Bermuda Atlantic Time Series (BATS) station in the Sargasso Sea. A five component model was fit to the EEMs, which included traditional terrestrial-like, marine-like, and protein-like components. Terrestrial-like components showed the expected high photo-reactivity, but surprisingly, the traditional marine-like peak showed slight photo-production in surface waters, which may account for its prevalence in marine systems. Surface waters were depleted in photo-labile components while protein-like fluorescent components were enriched, consistent with previous studies. Ultra-high resolution mass spectrometry detected unique aliphatic compounds in the surface waters at the BATS site, which may be photo-produced or photo-stable. Principle component and canonical analysis showed strong correlations between relative contributions of unsaturated/aromatic molecular formulas and depth, with aliphatic compounds more prevalent in surface waters and aromatic compounds in deep waters. Strong correlations were seen between these aromatic compounds and humic-like fluorescent components. The rapid photo-degradation of the deep-sea fluorescent DOM in addition to the surface water relative depletion of aromatic compounds suggests that deep-sea fluorescent DOM is very unlikely to survive overturning circulation

Ligands for Eu(III), Fe(III), Sr(II), and UO2(II) based on CMPO-functionalized resorcinarene cavitands; synthesis and extraction

Partially functionalized cavitands (7a–d) have been synthesized starting from the tetrakis(bromomethyl)cavitand 6. New cavitand‐based cation ligands, with one to three carbamoylmethylphosphane oxide (CMPO) moieties (11a–d), were prepared in good (66–90%) yields. The ligands 11a–d extract EuIII, but do so less effectively than the tetra‐CMPO cavitand 1. The decreasing number of CMPO groups which result in decreasing extraction percentages for EuIII, also decrease the selectivity of EuIII over that of FeIII, SrII, and UO2II. There is a difference in extraction behavior, determined by radio‐tracer experiments, between the distal and proximal disubstituted ligands, 11b and 11c, respectively. The extraction constants for the 1:1 complex of 11b and 11c with Eu(picrate)3 are Kex = 6.7 · 108 M−4 and 3.7 · 109 M−4, respectively