Organosulfur Molecules Research Articles

Thermally Triggered Interface for Simplified Organic Solar Cells

Organic photovoltaic (OPV) cells are commonly produced by successive printing of four layers on top of a transparent conducting electrode, with the active layer sandwiched in between interlayers followed by the top electrode. Here, the simplification of OPV manufacturing without the need to coat a hole transport layer (HTL) in inverted OPV (n–i–p) is reported. To ensure the required hole selectivity, thermally trigged molecules are directly blended in the active layer during device casting. Following thermal annealing of the complete devices, organosulfur molecules self‐assembled to form a hole–transporting interface between the silver top electrode and the active layer, thereby enabling working devices. Device optimization is performed by varying the concentration of these molecules and the thermal annealing conditions. The performances of the simplified devices approach those of control devices with vacuum‐evaporated MoO3 HTLs. The solar cells exhibit very encouraging thermal and photostabilities. This work opens the route to high efficiency, simplified, and low‐cost organic solar cells.

A computational study of the role of cobalt in thiophene adsorption on small Mo and MoCo clusters as site models for the HDS process

Non periodic density functional theory calculations are used to investigate the role of cobalt atoms in the adsorption of thiophene on small Mo and MoCo clusters. Metallic aggregates play the role of those active sites found in the true catalysts. Two interaction modes between thiophene and metallic sites are considered, namely, the S-mode, in which the organosulfur molecule interacts through the S atom, and the R-mode, in which the interaction takes place through the thiophene ring. A large number of sites, in which thiophene effectively adsorbs, was found, both in the monometallic case and in the bimetallic one. Considerably larger adsorption energies were found when thiophene interacts via the R-mode than when adsorption occurs through the S-mode. The activation of C-S bonds is also more important for R-mode cases than for S-mode ones. Further analysis made on some selected systems and based on density of states and molecular orbital overlap population-projected density of states reveals that thiophene and metallic clusters interact in an energy range around −6.0 eV with respect to the Fermi energy. Bands observed at energies below −6.0 eV correspond to thiophene states that become shifted with respect to the values obtained for isolated thiophene depending on the strength of the interaction. Bands above -6.0 eV describe how C and S atoms interact with Co and Mo ones, providing both bonding and antibonding patterns that helps to understand the overall interaction. Most important is the finding that cobalt atoms seem to play no relevant role during the adsorption of thiophene on metallic sites. Thus, present results obtained using non periodic GGA density functional theory seem to point to cobalt taking part in another step of the overall HDS process, hydrogen adsorption or hydrogen attack to C-S bonds, for instance.

Asymmetric by Design: Heteroleptic Coordination Compounds with Redox-Active Dithiolene and 1,2,4,5-Tetrakis(isopropylthio)benzene Ligands.

The 1,2,4,5-tetrakis(alkylthio)benzenes are redox-active organosulfur molecules that support oxidation to a stable radical cation. Their utility as ligands for the assembly of multimetal complexes with tailored functionality/property is unexamined. Here, 1,2,4,5-tetrakis(isopropylthio)benzene (tptbz, 1) is shown to bind PdCl2 at either one end, leaving the other open, or at both ends to form centrosymmetric [Cl2Pd(tptbz)PdCl2], 4. Ligand metathesis between Na2[(N≡C)2C2S2] (Na2mnt) and [Cl2M(tptbz)] (M = Pd, 2; M = Pt, 3) yields [(mnt)M(tptbz)] (M = Pd, 5; M = Pt, 6), but an alternative route involving transmetalation with [(mnt)SnMe2] delivers substantially greater yield. The mixed dithiolene-dithioether compound [(Ph2C2S2)Pt(tptbz)] (8) is formed by a similar transmetalation protocol using [(Ph2C2S2)SnnBu2]. Compounds 5, 6, and 8 are the first such heteroleptic complexes prepared by deliberate synthesis. The cyclic voltammetry of 8 reveals anodic waves at +0.14 and +0.97 V vs Fc+/Fc, which are attributed to successive dithiolene oxidation processes. While oxidized at +0.73 V as a free ligand, the redox-active MO of tptbz is pushed to a higher potential upon coordination to Pt2+ and is inaccessible. Calculations of the structures of [8]+ and of [((Cl2-3,5-C6H3)2C2S2)Pt(tptbz)]+ show that, in the latter, the dithiolene MOs are drawn down in energy into proximity with the tptbz MOs.

SAR92 clade bacteria are potentially important DMSP degraders and sources of climate-active gases in marine environments.

Catabolism of dimethylsulfoniopropionate (DMSP) by marine bacteria has important impacts on the global sulfur cycle and climate. However, whether and how members of most oligotrophic bacterial groups participate in DMSP metabolism in marine environments remains largely unknown. In this study, by characterizing culturable strains, we have revealed that bacteria of the SAR92 clade, an abundant oligotrophic group of Gammaproteobacteria in coastal seawater, can catabolize DMSP through the DMSP lyase DddD-mediated cleavage pathway and/or the DMSP demethylase DmdA-mediated demethylation pathway to produce climate-active gases dimethylsulfide and methanethiol. Additionally, we found that SAR92 clade bacteria capable of catabolizing DMSP are widely distributed in global oceans. These results indicate that SAR92 clade bacteria are potentially important DMSP degraders and sources of climate-active gases in marine environments that have been overlooked, contributing to a better understanding of the roles and mechanisms of the oligotrophic bacteria in oceanic DMSP degradation.

Genomic analysis of Marinomonas algicola SM1966T reveals its role in marine sulfur cycling.

Dimethylsulfoniopropionate (DMSP) is a ubiquitous organosulfur molecule in marine environments with important roles in global sulfur and nutrient cycling, which is mainly produced by marine phytoplankton and macroalgae. Marinomonas algicola SM1966T, a Gram-negative, aerobic and rod-shaped bacterium, was isolated from the surface of Ulva pertusa (Chlorophyta) algal sample collected off the coastal areas of Rongcheng, China. Here, we report the complete genome sequence of strain SM1966T and its genomic characteristics to utilize DMSP, which may be produced by Ulva pertusa. The genome of strain SM1966T contains one circular chromosome (4.3 Mbp) and one circular plasmid (149,271bp). Genomic analysis showed that strain SM1966T possesses a set of genes involved in DMSP transport, DMSP cleavage and the catabolism of acrylate, one product of DMSP cleavage. The results indicated that strain SM1966T has the capacity to utilize DMSP and produce dimethyl sulfide (DMS), a volatile infochemical with important roles in global sulfur cycling. This study provides genetic insights into DMSP catabolism by algae-associated bacteria.

Microbial Dimethylsulfoniopropionate Cycling in Deep Sediment of the Mariana Trench.

Dimethylsulfoniopropionate (DMSP) and related organic sulfur compounds play key roles in global sulfur cycling. Bacteria have been found to be important DMSP producers in seawater and surface sediments of the aphotic Mariana Trench (MT). However, detailed bacterial DMSP cycling in the Mariana Trench subseafloor remains largely unknown. Here, the bacterial DMSP-cycling potential in a Mariana Trench sediment core (7.5 m in length) obtained at a 10,816-m water depth was investigated using culture-dependent and -independent methods. The DMSP content fluctuated along the sediment depth and reached the highest concentration at 15 to 18 cm below the seafloor (cmbsf). dsyB was the dominant known DMSP synthetic gene, existing in 0.36 to 1.19% of the bacteria, and was identified in the metagenome-assembled genomes (MAGs) of previously unknown bacterial DMSP synthetic groups such as Acidimicrobiia, Phycisphaerae, and Hydrogenedentia. dddP, dmdA, and dddX were the major DMSP catabolic genes. The DMSP catabolic activities of DddP and DddX retrieved from Anaerolineales MAGs were confirmed by heterologous expression, indicating that such anaerobic bacteria might participate in DMSP catabolism. Moreover, genes involved in methanethiol (MeSH) production from methylmercaptopropionate (MMPA) and dimethyl sulfide (DMS), MeSH oxidation, and DMS production were highly abundant, suggesting active conversions between different organic sulfur compounds. Finally, most culturable DMSP synthetic and catabolic isolates possessed no known DMSP synthetic and catabolic genes, and actinomycetes could be important groups involved in both DMSP synthesis and catabolism in Mariana Trench sediment. This study extends the current understanding of DMSP cycling in Mariana Trench sediment and highlights the need to uncover novel DMSP metabolic genes/pathways in extreme environments. IMPORTANCE Dimethylsulfoniopropionate (DMSP) is an abundant organosulfur molecule in the ocean and is the precursor for the climate-active volatile gas dimethyl sulfide. Previous studies focused mainly on bacterial DMSP cycling in seawater, coastal sediment, and surface trench sediment samples, but DMSP metabolism in the Mariana Trench (MT) subseafloor sediments remains unknown. Here, we describe the DMSP content and metabolic bacterial groups in the subseafloor of the MT sediment. We found that the tendency for vertical variation of the DMSP content in the MT was distinct from that of the continent shelf sediment. Although dsyB and dddP were the dominant DMSP synthetic and catabolic genes in the MT sediment, respectively, both metagenomic and culture methods revealed multiple previously unknown DMSP metabolic bacterial groups, especially anaerobic bacteria and actinomycetes. The active conversion of DMSP, DMS, and methanethiol may also occur in the MT sediments. These results provide novel insights for understanding DMSP cycling in the MT.

Complex organosulfur molecules on comet 67P: Evidence from the ROSINA measurements and insights from laboratory simulations.

The ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument aboard the Rosetta mission revolutionized our understanding of cometary material composition. One of Rosetta's key findings is the complexity of the composition of comet 67P/Churyumov-Gerasimenko. Here, we used ROSINA data to analyze dust particles that were volatilized during a dust event in September 2016 and report the detection of large organosulfur species and an increase in the abundances of sulfurous species previously detected in the coma. Our data support the presence of complex sulfur-bearing organics on the surface of the comet. In addition, we conducted laboratory simulations that show that this material may have formed from chemical reactions that were initiated by the irradiation of mixed ices containing H2S. Our findings highlight the importance of sulfur chemistry in cometary and precometary materials and the possibility of characterizing organosulfur materials in other comets and small icy bodies using the James Webb Space Telescope.

Roles of phytoplankton, microzooplankton, and bacteria in DMSP and DMS transformation processes in the East China Continental Sea

The trace gas dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) are the most abundant oceanic biogenic organosulfur molecules. Phytoplankton, zooplankton, and bacteria are the most vital biotic factors controlling DMSP and DMS, but their relative effects on the transformation processes still remain uncertain due to their complex biogeochemistry. Here, we provided the relative transformation rates of DMSP and DMS, and their relationships with phytoplankton, microzooplankton, and bacteria in the East China Continental Sea in the summer of 2018. The phytoplankton was the major DMSP producer, contributing 89.8% of DMSP stock with the particulate DMSP production rate at 42.0 nmol L−1 d−1. The DMSP lyase activity was 140.5 nmol DMS L−1h−1, resulting in a short DMSP fate (0.8 d). The microzooplankton grazing resulted in DMSP loss and DMS production at the rates of −49.3 and 8.2 nmol L−1 d−1, equaling 60.0% of total DMSP loss and 71.6% of DMS microbial production. The dissolved DMSP degradation and DMS microbial production rates were at −23.4 and 11.5 nmol L−1 d−1, largely controlled by bacterial abundance. Microbial consumption, photolysis, and ventilation accounted for 41%, 43%, and 16% of surface DMS removal, indicating that most of the DMS was consumed within the surface. Finally, DMS was enriched in the sediment but not significantly enriched in the surface microlayer, with enrichment factors at 3.7 and 1.0, respectively. The budget model in this study could help better estimate the roles of phytoplankton, microzooplankton, and bacteria in DMSP and DMS transformation processes in the continental shelf seas.

Integrating microsecond timescale classical and biased molecular dynamics simulations to screen potential molecules for BRD4-BD1

Contemporary pre-clinical drug discovery is complemented by the combinatorial use of numerous computational techniques linked to computer-aided drug design and discovery. We combined inherently different computational analyses derived from multi-scale conventional, steered and umbrella sampling simulations to identify potential drug candidates for the first bromodomain of the human bromodomain containing protein 4 (BRD4-BD1). The BRD4-BD1 protein is a recognized therapeutic target for various diseases including cancer, neurological disorders, inflammation, and obesity. The in-house synthesized benzosuberene-sulfone (BSS) molecules were assessed for their potential to act as inhibitors against the BRD4-BD1 protein. We compared the molecular interactions and docking scores of BSS analogues with six different co-crystal inhibitors of the BRD4-BD1 protein. Further, the thermodynamic free energy of binding for each complex was estimated by the end-state Molecular Mechanics Poisson-Boltzmann Surface Area (MM/PBSA) approach. Moreover, umbrella sampling simulations were utilized to validate the results obtained from MM/PBSA analyses and to demonstrate the unbinding/binding process of the most potent BSS analogue from the binding pocket of BRD4-BD1 protein. Our results show the potential of organosulfur molecules to be developed as inhibitors of the BRD4-BD1 protein and endorse their evaluation by suitable in-vitro and in-vivo studies.

Dietary organosulfur compounds: Emerging players in the regulation of bone homeostasis by plant-derived molecules.

The progressive decline of bone mass and the deterioration of bone microarchitecture are hallmarks of the bone aging. The resulting increase in bone fragility is the leading cause of bone fractures, a major cause of disability. As the frontline pharmacological treatments for osteoporosis suffer from low patients’ adherence and occasional side effects, the importance of diet regimens for the prevention of excessive bone fragility has been increasingly recognized. Indeed, certain diet components have been already associated to a reduced fracture risk. Organosulfur compounds are a broad class of molecules containing sulfur. Among them, several molecules of potential therapeutic interest are found in edible plants belonging to the Allium and Brassica botanical genera. Polysulfides derived from Alliaceae and isothiocyanates derived from Brassicaceae hold remarkable nutraceutical potential as anti-inflammatory, antioxidants, vasorelaxant and hypolipemic. Some of these effects are linked to the ability to release the gasotrasmitter hydrogen sulfide (H2S). Recent preclinical studies have investigated the effect of organosulfur compounds in bone wasting and metabolic bone diseases, revealing a strong potential to preserve skeletal health by exerting cytoprotection and stimulating the bone forming activity by osteoblasts and attenuating bone resorption by osteoclasts. This review is intended for revising evidence from preclinical and epidemiological studies on the skeletal effects of organosulfur molecules of dietary origin, with emphasis on the direct regulation of bone cells by plant-derived polysulfides, glucosinolates and isothiocyanates. Moreover, we highlight the potential molecular mechanisms underlying the biological role of these compounds and revise the importance of the so-called ‘H2S-system’ on the regulation of bone homeostasis.

Oceanospirillales containing the DMSP lyase DddD are key utilisers of carbon from DMSP in coastal seawater

BackgroundUbiquitous and diverse marine microorganisms utilise the abundant organosulfur molecule dimethylsulfoniopropionate (DMSP), the main precursor of the climate-active gas dimethylsulfide (DMS), as a source of carbon, sulfur and/or signalling molecules. However, it is currently difficult to discern which microbes actively catabolise DMSP in the environment, why they do so and the pathways used.ResultsHere, a novel DNA-stable isotope probing (SIP) approach, where only the propionate and not the DMS moiety of DMSP was 13C-labelled, was strategically applied to identify key microorganisms actively using DMSP and also likely DMS as a carbon source, and their catabolic enzymes, in North Sea water. Metagenomic analysis of natural seawater suggested that Rhodobacterales (Roseobacter group) and SAR11 bacteria were the major microorganisms degrading DMSP via demethylation and, to a lesser extent, DddP-driven DMSP lysis pathways. However, neither Rhodobacterales and SAR11 bacteria nor their DMSP catabolic genes were prominently labelled in DNA-SIP experiments, suggesting they use DMSP as a sulfur source and/or in signalling pathways, and not primarily for carbon requirements. Instead, DNA-SIP identified gammaproteobacterial Oceanospirillales, e.g. Amphritea, and their DMSP lyase DddD as the dominant microorganisms/enzymes using DMSP as a carbon source. Supporting this, most gammaproteobacterial (with DddD) but few alphaproteobacterial seawater isolates grew on DMSP as sole carbon source and produced DMS. Furthermore, our DNA-SIP strategy also identified Methylophaga and other Piscirickettsiaceae as key bacteria likely using the DMS, generated from DMSP lysis, as a carbon source.ConclusionsThis is the first study to use DNA-SIP with 13C-labelled DMSP and, in a novel way, it identifies the dominant microbes utilising DMSP and DMS as carbon sources. It highlights that whilst metagenomic analyses of marine environments can predict microorganisms/genes that degrade DMSP and DMS based on their abundance, it cannot disentangle those using these important organosulfur compounds for their carbon requirements. Note, the most abundant DMSP degraders, e.g. Rhodobacterales with DmdA, are not always the key microorganisms using DMSP for carbon and releasing DMS, which in this coastal system were Oceanospirillales containing DddD.98tW24pEex88JAHxuSH5r1Video abstract.

Mechanistic insights into the key marine dimethylsulfoniopropionate synthesis enzyme DsyB/DSYB.

Marine algae and bacteria produce approximately eight billion tonnes of the organosulfur molecule dimethylsulfoniopropionate (DMSP) in Earth's surface oceans annually. DMSP is an antistress compound and, once released into the environment, a major nutrient, signaling molecule, and source of climate-active gases. The methionine transamination pathway for DMSP synthesis is used by most known DMSP-producing algae and bacteria. The S-directed S-adenosylmethionine (SAM)-dependent 4-methylthio-2-hydroxybutyrate (MTHB) S-methyltransferase, encoded by the dsyB/DSYB gene, is the key enzyme of this pathway, generating S-adenosylhomocysteine (SAH) and 4-dimethylsulfonio-2-hydroxybutyrate (DMSHB). DsyB/DSYB, present in most haptophyte and dinoflagellate algae with the highest known intracellular DMSP concentrations, is shown to be far more abundant and transcribed in marine environments than any other known S-methyltransferase gene in DMSP synthesis pathways. Furthermore, we demonstrate in vitro activity of the bacterial DsyB enzyme from Nisaea denitrificans and provide its crystal structure in complex with SAM and SAH-MTHB, which together provide the first important mechanistic insights into a DMSP synthesis enzyme. Structural and mutational analyses imply that DsyB adopts a proximity and desolvation mechanism for the methyl transfer reaction. Sequence analysis suggests that this mechanism may be common to all bacterial DsyB enzymes and also, importantly, eukaryotic DSYB enzymes from e.g., algae that are the major DMSP producers in Earth's surface oceans.

The Bifurcated σ-Hole···σ-Hole Stacking Interactions.

The bifurcated σ-hole···σ-hole stacking interactions between organosulfur molecules, which are key components of organic optical and electronic materials, were investigated by using a combined method of the Cambridge Structural Database search and quantum chemical calculation. Due to the geometric constraints, the binding energy of one bifurcated σ-hole···σ-hole stacking interaction is in general smaller than the sum of the binding energies of two free monofurcated σ-hole···σ-hole stacking interactions. The bifurcated σ-hole···σ-hole stacking interactions are still of the dispersion-dominated noncovalent interactions. However, in contrast to the linear monofurcated σ-hole···σ-hole stacking interaction, the contribution of the electrostatic energy to the total attractive interaction energy increases significantly and the dispersion component of the total attractive interaction energy decreases significantly for the bifurcated σ-hole···σ-hole stacking interaction. Another important finding of this study is that the low-cost spin-component scaled zeroth-order symmetry-adapted perturbation theory performs perfectly in the study of the bifurcated σ-hole···σ-hole stacking interactions. This work will provide valuable information for the design and synthesis of novel organic optical and electronic materials.

S-Allylcysteine Ameliorates Aging Features via Regulating Mitochondrial Dynamics in Naturally Aged C57BL/6J Mice.

S-Allylcysteine (SAC) is the most abundant organosulfur molecule derived from aged garlic. The effects ofSAC on improving Aging in naturally aged C57BL/6J male mice and mitochondrial dynamics in Caenorhabditis elegans and its underlying mechanisms is evaluated. When mice have attained reproductive senescence at 60 weeks of age, SAC is supplemented to 0.05% and 0.2% into their normal diet for 12 weeks. The results show that SAC could significantly improve the level of hepatic optic atrophy 1 (OPA1) mRNA, which is a key factor for mitochondrial fusion, and consequently elevated the mitochondrial biogenesis-related proteins sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α), thus ameliorating oxidative stress, such as malondialdehyde (MDA) in the liver and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in urine. Among the biochemical markers of aging, SAC significantly reduces liver galactosidase β1 (GLB1) and senescence-associated β-galactosidase (SA-βgal), which are induced by replicative senescence. The mitochondria with green fluorescent protein (GFP)-tagged transgenic strain SJ4103 C. elegans is incubated with 5 or 50µM SAC, and SAC treated groups maintain the linear morphology of mitochondria. SAC regulates mitochondrial dynamics and ameliorated aging to a significant degree. This study also confirms that mitochondrial dynamics are a promising target for screening materials to combat aging and as a direction for anti-aging product development.

Computational Studies of MoS2 Nanotubes for Hydrodesulfurization

Due to environmental restrictions that are increasingly severe, elimination of sulfur from petroleum feedstocks is necessary. MoS2 NTs have several applications, though there is little information about the applicability of these materials in hydrorefining processes. DFT calculations were employed to predict the formation energy, Gibbs free energy, and energy barriers of the sulfur vacancy for pristine and Co-doped MoS2 nanotubes. In order to gain more insight about the accessibility of the catalytic sites, a group of small organosulfur molecules was studied by force-field-based molecular dynamics in which it was possible to confirm that these species are able to enter the nanotube channel, thus reaching a possible sulfur vacancy. DFT calculations were once again carried out to study the interaction between the guest organosulfur molecules and the sulfur vacancies, enabling the observation of possible chemisorption phenomena. The computational results demonstrated that the bending of the MoS2 nanosheet, compared to the flat monolayer, favors formation of the sulfur vacancy as well as the interaction between the studied guest molecules and the active site.

Theoretical studies of unimolecular decomposition of thiophene at high temperatures

Thiophene is an organo-sulfur aromatic molecule present in fossil fuels and alternate fuels such as shale oils and contributes to air pollution via fuel burning. Hence, it is essential to remove thiophene and its derivatives during the refining process. In this regard, experimental and electronic structure theory studies investigating the thermal decomposition of thiophene have been reported in the literature. In the present work, high temperature thermal decomposition of thiophene was investigated using Born–Oppenheimer direct dynamics simulations. The trajectory integrations were performed on-the-fly at the density functional B3LYP/6-31+G* level of electronic structure theory to investigate the atomic level decomposition mechanisms. Simulation results show that C–S cleavage accompanied by an intramolecular proton transfer to C is the dominant initial dissociation step. Acetylene was observed as primary decomposition product and the results are in agreement with previous experimental studies.

Advances of Organosulfur Materials for Rechargeable Metal Batteries.

Battery materials have become a hotspot in the academic research. Organosulfur compounds are considered as a promising class of cathode materials for rechargeable metal batteries. They have attracted increasing attention in recent years after a long‐term stagnancy since 1980s. Recent studies have focused on the understanding of redox mechanism of linear organosulfur molecules R‐S n ‐R with defined structures. In addition, some new organosulfur compounds are developed. The reversible sulfur—sulfur (S—S) bond breakage/formation of organosulfur in batteries makes them applicable as functional materials in batteries. In this review, new organosulfur materials including molecules, polymers, and composites are introduced. In the following, organosulfur‐inorganic hybrid materials are discussed, which have shown unique redox process and enhanced battery performance. In the third part, organosulfur additives are used in Li‐S batteries, which can improve the formation of solid‐electrolyte interphase (SEI) and alter the redox pathways of sulfur cathodes. In the fourth part, organosulfur materials used in other metal batteries are introduced. Lastly, a summary and some perspectives are given. This review presents an overview of the recent advances of organosulfur materials in batteries and provides guidance for the future development of these materials.

Dimethylsulfoniopropionate and dimethylsulfoxide in Posidonia oceanica

The present work aims at determining the natural variability of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) contents in the seagrass Posidonia oceanica, which is the largest producer of these molecules reported to date among coastal autotrophs. Seagrass leaf samples were collected during a period of 3.5 years in the pristine Revellata Bay (Calvi, northwestern Corsica, France). The DMSP content ranged from 25 to 265 µmol.gfw−1; DMSO from 1.0 to 13.9 µmol.gfw−1. The dynamics of the two molecules were closely linked, the DMSO content being equivalent to 3.5% of the DMSP content, all leaf samples considered (n = 423 samples and 414 DMSP(O) data pairs). The annual growth cycle of the seagrass diluted the initial stocks of the two molecules. Temperature indirectly affected molecule content dynamics through their direct effect on the seagrass productivity and biomass. Inter-annual variations in DMSP(O) content in relation to shallow water temperature might further indicate that DMSP(O) could have been involved in the physiological response of P. oceanica to heat stress. Finally, middle-aged leaf tissues with an organosulfur molecule content similar to the average value calculated for the seagrass leaf bundle appeared to be the best choice of sample material to study DMSP and DMSO in that species. More research is needed to elucidate the biosynthetic pathways of these molecules in seagrasses, the evolutionary reasons for such a high production in P. oceanica and the physiological functions they play.

Dimethylsulfoniopropionate Biosynthetic Bacteria in the Subseafloor Sediments of the South China Sea.

Dimethylsulfoniopropionate (DMSP) is one of Earth’s most abundant organosulfur molecules, and bacteria in marine sediments have been considered significant producers. However, the vertical profiles of DMSP content and DMSP-producing bacteria in subseafloor sediment have not been described. Here, we used culture-dependent and -independent methods to investigate microbial DMSP production and cycling potential in South China Sea (SCS) sediment. The DMSP content of SCS sediment decreased from 11.25 to 20.90 nmol g–1 in the surface to 0.56–2.08 nmol g–1 in the bottom layers of 8-m-deep subseafloor sediment cores (n = 10). Very few eukaryotic plastid sequences were detected in the sediment, supporting bacteria and not algae as important sediment DMSP producers. Known bacterial DMSP biosynthesis genes (dsyB and mmtN) were only predicted to be in 0.0007–0.0195% of sediment bacteria, but novel DMSP-producing isolates with potentially unknown DMSP synthesis genes and/or pathways were identified in these sediments, including Marinobacter (Gammaproteobacteria) and Erythrobacter (Alphaproteobacteria) sp. The abundance of bacteria with the potential to produce DMSP decreased with sediment depth and was extremely low at 690 cm. Furthermore, distinct DMSP-producing bacterial groups existed in surface and subseafloor sediment samples, and their abundance increased when samples were incubated under conditions known to enrich for DMSP-producing bacteria. Bacterial DMSP catabolic genes were also most abundant in the surface oxic sediments with high DMSP concentrations. This study extends the current knowledge of bacterial DMSP biosynthesis in marine sediments and implies that DMSP biosynthesis is not only confined to the surface oxic sediment zones. It highlights the importance of future work to uncover the DMSP biosynthesis genes/pathways in novel DMSP-producing bacteria.

New approach for assigning mean oxidation number of carbons to organonitrogen and organosulfur compounds

Abstract Organonitrogen and organosulfur compounds are abundant in the natural environment. To understand the biological redox pathways properly, it is important for learners to be able to count the oxidation number of organic carbons. However, the process of counting is not always easy. In addition, organonitrogen and organosulfur molecules are seldom studied. To compensate these problems, this paper explores the bond-dividing method, which can effectively determine the mean oxidation number of carbons of organonitrogen and organosulfur molecules. This method uses the cleavage of carbon-sulfur and carbon-nitrogen bonds to obtain the organic and inorganic fragments. The mean oxidation numbers of carbon atoms, nitrogen atoms, and sulfur atoms can be calculated by the molecular formulas of their fragments. Furthermore, when comparing organosulfur or organonitrogen molecules in a redox conversion, the changes of the mean oxidation numbers of carbon atoms, nitrogen atoms, and sulfur atoms can be used as indicators to identify the redox positions and determine the number of transferred electrons.