Hong-Hai Zhang

Molecular insight into bacterial cleavage of oceanic dimethylsulfoniopropionate into dimethyl sulfide

Significance DMS is an important participant in the global sulfur and carbon cycles. DMS oxidation products cause the formation of cloud condensation nuclei and hence may influence weather and climate. DMS is produced through the cleavage of dimethylsulfoniopropionate (DMSP) mainly by marine bacterial DMSP lyases. The molecular mechanism of DMSP cleavage to generate DMS remains unclear. In this study, the crystal structure of DddQ, a DMSP lyase, was solved, and detailed biochemical and structural analyses were performed. Our results also provided a foremost insight into the catalytic mechanism of the DMSP cleavage reaction. This study offers a better understanding of how marine bacteria cleave DMSP to generate the climatically important gas DMS. The microbial cleavage of dimethylsulfoniopropionate (DMSP) generates volatile DMS through the action of DMSP lyases and is important in the global sulfur and carbon cycles. When released into the atmosphere from the oceans, DMS is oxidized, forming cloud condensation nuclei that may influence weather and climate. Six different DMSP lyase genes are found in taxonomically diverse microorganisms, and dddQ is among the most abundant in marine metagenomes. Here, we examine the molecular mechanism of DMSP cleavage by the DMSP lyase, DddQ, from Ruegeria lacuscaerulensis ITI_1157. The structures of DddQ bound to an inhibitory molecule 2-(N-morpholino)ethanesulfonic acid and of DddQ inactivated by a Tyr131Ala mutation and bound to DMSP were solved. DddQ adopts a β-barrel fold structure and contains a Zn2+ ion and six highly conserved hydrophilic residues (Tyr120, His123, His125, Glu129, Tyr131, and His163) in the active site. Mutational and biochemical analyses indicate that these hydrophilic residues are essential to catalysis. In particular, Tyr131 undergoes a conformational change during catalysis, acting as a base to initiate the β-elimination reaction in DMSP lysis. Moreover, structural analyses and molecular dynamics simulations indicate that two loops over the substrate-binding pocket of DddQ can alternate between “open” and “closed” states, serving as a gate for DMSP entry. We also propose a molecular mechanism for DMS production through DMSP cleavage. Our study provides important insight into the mechanism involved in the conversion of DMSP into DMS, which should lead to a better understanding of this globally important biogeochemical reaction.

Spatial variation of biogenic sulfur in the south Yellow Sea and the East China Sea during summer and its contribution to atmospheric sulfate aerosol

Spatial distributions of biogenic sulfur compounds including dimethylsulfide (DMS), dissolved and particulate dimethylsulfoniopropionate (DMSPd and DMSPp) were investigated in the South Yellow Sea (SYS) and the East China Sea (ECS) in July 2011. The concentrations of DMS and DMSPp were significantly correlated with the levels of chlorophyll a in the surface water. Simultaneously, relatively high ratio values of DMSP/chlorophyll a and DMS/chlorophyll a occurred in the areas where the phytoplankton community was dominated by dinoflagellates. The DMSPp and chlorophyll a size-fractionation showed that larger nanoplankton (5-20 μm) was the most important producer of DMSPp in the study area. The vertical profiles of DMS and DMSP were characterized by a maximum at the upper layer and the bottom concentrations were also relatively higher compared with the overlying layer of the bottom. In addition, a positive linear correlation was observed between dissolved dimethylsulfoxide (DMSOd) and DMS concentrations in the surface waters. The sea-to-air fluxes of DMS in the study area were estimated to be from 0.03 to 102.35 μmol m(-2) d(-1) with a mean of 16.73 μmol m(-2) d(-1) and the contribution of biogenic non-sea-salt SO4(2-) (nss-SO4(2-)) to the measured total nss-SO4(2-) in the atmospheric aerosol over the study area varied from 1.42% to 30.98%, with an average of 8.2%.

Occurrence, distribution, and ecological risks of phthalate esters in the seawater and sediment of Changjiang River Estuary and its adjacent area

A total of 133 seawater samples and 17 sediment samples were collected from 81 sampling sites in the Changjiang River Estuary and its adjacent area and were analyzed for 16 phthalate esters (PAEs). The Σ16 PAE concentrations in the seawater and sediment samples ranged from 180.3ng·L-1 to 3421ng·L-1 and from 0.48μg·g-1 to 29.94μg·g-1dry weight (dw), respectively, with mean values of 943.6ng·L-1 and 12.88μg·g-1. The distribution of ∑16PAE concentrations in the water column showed that PAE concentrations in the bottom samples were higher than those in the surface samples (except the transect C located inside the Changjiang River Estuary), with the maxima appearing in the bottom layer at the offshore stations. Among the 16 PAEs, di (2-ethylhexyl) phthalate (DEHP), diisobutyl phthalate (DiBP), and dibutyl phthalate (DnBP) dominated the PAEs, with 25.1%, 21.1%, and 18.9% of the Σ16PAEs in seawater, respectively. The comparison of ∑16PAEs and salinities in transects C and A6 suggested that the Changjiang River runoff was an important driving factor influencing the distribution of PAEs. DEHP concentrations in water samples and DEHP and DnBP concentrations in sediment samples exceeded the environmental risk levels (ERL), indicating their potential hazard to the ocean environment.

Distributions and sea-to-air fluxes of chloroform, trichloroethylene, tetrachloroethylene, chlorodibromomethane and bromoform in the Yellow Sea and the East China Sea during spring

Halocarbons including chloroform (CHCl3), trichloroethylene (C2HCl3), tetrachloroethylene (C2Cl4), chlorodibromomethane (CHBr2Cl) and bromoform (CHBr3) were measured in the Yellow Sea (YS) and the East China Sea (ECS) during spring 2011. The influences of chlorophyll a, salinity and nutrients on the distributions of these gases were examined. Elevated levels of these gases in the coastal waters were attributed to anthropogenic inputs and biological release by phytoplankton. The vertical distributions of these gases in the water column were controlled by different source strengths and water masses. Using atmospheric concentrations measured in spring 2012 and seawater concentrations obtained from this study, the sea-to-air fluxes of these gases were estimated. Our results showed that the emissions of C2HCl3, C2Cl4, CHBr2Cl, and CHBr3 from the study area could account for 16.5%, 10.5%, 14.6%, and 3.5% of global oceanic emissions, respectively, indicating that the coastal shelf may contribute significantly to the global oceanic emissions of these gases.

Biogeochemistry of dimethylsulfoniopropionate, dimethylsulfide and acrylic acid in the Yellow Sea and the Bohai Sea during autumn

Environmental context Dimethylsulfide (DMS) is a climatically important biogenic trace gas that is emitted from oceans. This research focuses on the spatiotemporal distributions of DMS and its related compounds, i.e. dimethylsulfoniopropionate (DMSP) and acrylic acid (AA), and the influencing factors in the Yellow Sea and the Bohai Sea during autumn. In addition, the sea-to-air flux of DMS, kinetic responses of DMSP consumption as well as DMS and AA production are also investigated. This study is helpful in understanding the marine sulfur cycle in marginal seas in China. Abstract The biogeochemistry of dimethylsulfoniopropionate (DMSP), dimethylsulfide (DMS) and acrylic acid (AA) in the Yellow Sea (YS) and the Bohai Sea (BS) was investigated in November 2013. The concentrations (and ranges) of total DMSP (DMSPt), dissolved DMSP (DMSPd), DMS and AA in surface waters were 30.71 (1.07–122.50), 6.60 (0.85–35.67), 1.48 (0.53–5.32) and 42.2 (13.8–352.8) nmol L–1 respectively. The concentrations of DMSPd and AA were positively correlated with chlorophyll-a levels, which suggests that phytoplankton biomass has an important function in controlling DMSPd and AA distributions. Furthermore, DMS and AA concentrations revealed significant positive relationships with DMSPd concentrations. The average ratios of AA/(DMSP+AA) and DMS/AA were 53.98 and 7.62% respectively. The vertical profiles of DMSP, DMS and AA were characterised by high concentrations that mostly occur near the surface. Even under highly variable hydrographic conditions, a positive relationship was observed between DMSPt and chlorophyll-a concentrations. The rates of DMSPd consumption, as well as DMS and AA production, significantly varied with marine environments. The sea-to-air fluxes of DMS from the YS and the BS to the atmosphere were estimated to be in the range of 3.01 to 6.91μmol m–2day–1.

Chemical Characteristics of Aerosol Composition over the Yellow Sea and the East China Sea in Autumn

AbstractThe total suspended particulate (TSP) samples over the Yellow Sea and the East China Sea were collected to determine the major compositions of water-soluble ionic species during two cruises in autumn 2007. The aerosol compositions exhibited an obvious regional variation between the two cruises, with higher concentrations (except Na+ and Mg2+) over the northern Yellow Sea during the first cruise. The concentrations of the secondary ions [non–sea salt sulfate (nss-), , and ] were 11 ± 4.9, 3.1 ± 2.1, and 3.7 ± 2.6 μg m−3, respectively, which together contributed over 72% of the total determined ion concentrations. Significant correlations between these secondary ions were found within each sampling period, while nss-K+ and nss-Ca2+ showed strong correlation with each other. The calculated results of equivalent concentrations of anions (nss- and ) and cations ( and Ca2+) showed that the acidic species were mostly neutralized with the alkaline species over the study areas. The mass ratio of nss-/ was ...

Temporal and spatial variations of three dimethylated sulfur compounds in the Changjiang Estuary and its adjacent area during summer and winter

Environmental context Dimethylsulfide is a biogeochemically important sulfur gas emitted from the oceans that can lead to aerosol formation, thereby affecting earth albedo and climate. Studies on the biogeochemistry of dimethylsulfide and its precursors and oxidation products in coastal waters can link the atmospheric chemistry of dimethylsulfide with the bioavailable organic sulfur pool in the oceans. The ensuing information is essential for understanding the biogeochemical dynamics of sulfur and its global cycles. Abstract The spatiotemporal distribution patterns of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO) and chlorophyll a (Chl-a), as well as the oceanographic parameters influencing the concentrations of DMS, DMSP and DMSO, were measured in the Changjiang Estuary and its adjacent area during two cruises from 21 February to 10 March 2014 and from 10 to 22 July 2014. The concentrations of DMS and DMSP showed significant seasonal variation, i.e. higher values in summer than in winter. This result corresponded well with the seasonal change in Chl-a in the study area. The distribution of dissolved DMSO (DMSOd) decreased significantly with distance from shore, suggesting a primary source of terrestrial and riverine inputs. The seasonal variations of both DMSOd and particulate DMSO (DMSOp) were weaker than other sulfur compounds. Significant relationships were observed between DMS, particulate DMSP (DMSPp), DMSOp and Chl-a, suggesting that phytoplankton biomass plays an important role in controlling the distributions of DMS, DMSP and DMSO in the study area. The positive relationship between DMSPp and DMSOp suggested similar sources and cellular functions in algae, whereas the oxidation of DMS to DMSOd appeared to be a predominant source of DMSOd in winter in the area adjacent to the river mouth. The average sea-to-air fluxes of DMS in the Changjiang Estuary and its adjacent area were 0.37 and 1.70 µmol m–2 day–1 in winter and summer respectively; these values are much lower than those in other continental shelf seas.

Photochemical behavior of dissolved and colloidal organic matter in estuarine and oceanic waters

Chromophoric dissolved organic matter (CDOM), carbohydrates, and amino acids were analyzed to investigate the photochemistry of total dissolved (<0.22μm) organic matter (DOM), high-molecular-weight (HMW, 1kDa-0.22μm) DOM and low-molecular-weight (LMW, <1kDa) DOM at stations in the Yangtze River and its coastal area, and in the Western Pacific Ocean. Results revealed that the humic-like and tryptophan-like CDOM fluorescent components in riverine, coastal, and oceanic surface waters were photodegraded during irradiation. However, the photochemical behavior of tyrosine-like component was obscured by the excessive fluorescence intensities of humic- and tryptophan-like fluorescent components. Light sensitivity varied depending on the source material; terrestrially derived DOM was more susceptible to irradiation than autochthonous DOM. In contrast to the expected photodegradation of CDOM, photo-induced synthetic reaction transformed the LMW matters to polysaccharides (PCHO) and degradation reaction decomposed the HMW DOM to Monosaccharides. Colloidal DOM preferentially underwent photodegradation, whereas permeate DOM mainly photosynthesized PCHO. The total hydrolysable amino acid (THAA) pool changed because of the additional input by the photodegradation of DOM or THAA itself. The compositions of THAA changed during the irradiation experiments, indicating that the different photochemical behavior of individual amino acids were related to their different original photoreactivities; the relatively stable amino acids (e.g., Ser and Gly) significantly accumulated during irradiation, whereas photo-active aromatic amino acids (e.g. Tyr and His) were prone to photodegradation. The data presented here demonstrated that irradiation significantly influence the conversion between dissolved and colloid organic matter. These results can promote the understanding of irradiation effect on the carbon and nitrogen cycle in riverine, estuarine and oceanic ecosystems.

A Study on the Release of Oil from Oil-Contaminated Sediment Through Laboratory Experiments

The release of heavy oil from laboratory-contaminated sediments was studied in a series of kinetic and equilibrium experiments. The kinetic curves could be interpreted by a two-compartment first-order equation including rapid and slow release steps. The slow step was dominant and the rate constant was 3 orders of magnitude smaller than for the rapid step. Equilibrium experiments for the slow step revealed that the isotherms could be described by the Freundlich equation. The release of heavy oil was found to correlate with higher contamination level, larger particle size, lower salinity, and higher temperature. The effect of coexisting surfactant on the release was also investigated and the results showed that the presence of Tween-20 promoted the process. The oil release process was endothermic and the randomness at the solid–liquid interface increased during the desorption process. The values of activation energy and standard enthalpy change indicated that this process was a physical one.

Distribution and ecotoxicological state of phthalate esters in the sea-surface microlayer, seawater and sediment of the Bohai Sea and the Yellow Sea

The spatial distribution, chemical composition and ecological risk of 16 phthalate esters (PAEs) were investigated in the sea-surface microlayer (SML), seawater and sediment samples of the Bohai Sea (BS) and the Yellow Sea (YS). The concentration levels of the ΣPAEs spanned a range of 449-13441 ng L-1 in the SML, 453-5108 ng L-1 in seawater, and 1.24-15.8 mg kg-1 in the sediment samples, respectively, with diisobutyl phthalate (DiBP), di-n-butyl phthalate (DBP) and di-ethylhexyl phthalate (DEHP) as the dominant PAEs in both the water and sediment samples. The concentrations of ΣPAEs in the BS were higher than those in the YS. The vertical distribution of ΣPAEs in the water column showed that the concentrations were higher in the surface waters, but decreased slightly with depth, and started to increase at the bottom. Additionally, PAEs were significantly enriched in the SML, with an average enrichment factor of 1.46. The ecological risk of the PAEs was evaluated by the risk quotient (RQ) method, which indicated that DEHP posed a high risk to aquatic organisms in the whole water-phase, while the RQ values of DBP and DiBP reached a high risk levels in sedimentary environment.