Production of dimethyl sulfide and acrylic acid from dissolved dimethylsulfoniopropionate during the growth of Prorocentrum minimum

Journal of Applied Phycology - Dimethyl sulfide (DMS) is an important and dominant trace gas that is transferred from the ocean to the atmosphere; however, the production of DMS from marine algae...     

Distribution of dimethylsulfide and dimethylsulfoniopropionate and its relation with phytoneuston in the surface microlayer of the western North Atlantic during summer

One of the key steps towards predicting dimethylsulfide (DMS) emission to the atmosphere is to understand the distribution and cycling of biogenic sulfur in the microlayer. In this study, we examined the distribution of DMS and dissolved and particulate fractions of dimethylsulfoniopropionate (DMSPd and DMSPp) in the surface microlayer and bulk water of the western North Atlantic during July 2003. DMS concentrations in the bulk water varied from 0.71 to 7.65 nM. In contrast, DMS concentrations in the surface microlayer were fairly low (0.17–1.33 nM). Average concentrations of DMSPd and DMSPp in the bulk water were 2.09 (1.87–6.25) and 44.1 (8.06–119.8) nM, respectively, and those in the surface microlayer were 15.4 (4.06–54.3) and 29.9 (7.32–97.0) nM. In general, DMS was depleted in the microlayer (mean concentration: 0.60 nM) relative to the bulk water (mean concentration: 2.38 nM) with enrichment factors (the ratio of the microlayer concentration to bulk water concentration) ranging from 0.13 to 0.54. There was no consistent enrichment of DMSPp and chlorophyll a in the microlayer. On the contrary, DMSPd appeared to be highly enriched in the microlayer with an average EF of 4.89. The concentration of phaeopigments was also generally greater in the microlayer than in the bulk water, presumably due to enhanced photo-oxidation of chlorophyll a under high surface light intensities in the microlayer. In the study area, the concentration of DMSPp was significantly correlated with the abundance of dinoflagellates in the microlayer. Moreover, a significant correlation between the distributions of DMS, DMSPp, chlorophyll a and phaeopigment concentrations in the microlayer and the bulk water demonstrated that the biogenic materials in the microlayer come primarily from the bulk water below.     

一株海洋低温葡萄糖氧化酶菌株的筛选、鉴定及部分酶学性质

【目的】从海洋样品中分离筛选出产葡萄糖氧化酶菌株。【方法】采用双层平板筛选法进行初筛、复筛确定一株酶活较好的菌株,命名为GOD2(Glucose oxidase)。通过形态学、生理生化特征及16S rRNA基因序列分析研究其分类地位,并对其产生的葡萄糖氧化酶进行分离纯化和部分酶学性质的研究。【结果】细菌GOD2为产葡萄糖氧化酶菌株且遗传稳定,初步鉴定该菌株为假单胞杆菌(Pseudomonas migulae),其所产酶最适反应温度为20°C,热稳定性较差,40°C剩余相对酶活80%;超过40°C酶活力迅速下降。【结论】GOD2是一株极具研究价值的产低温葡萄糖氧化酶菌株。目前没有关于利用该菌生产葡萄糖氧化酶的报道。     

Spatio-temporal variations of sea surface halocarbon concentrations and fluxes from southern Yellow Sea

Temporal and spatial distributions of five volatile halogenated organic compounds (VHOC), including chloroform (CHCl₃), trichloroethylene (C₂HCl₃), bromodichloromethane (CHBrCl₂), chlorodibromomethane (CHBr₂Cl), and bromoform (CHBr₃), were determined in the southern Yellow Sea (SYS) during four cruises from July 2008 to May 2009. The five VHOC distributed in the study area were affected by river inputs, anthropogenic activities, circulation system, and biological processes. In this study, CHCl₃, CHBrCl₂, CHBr₂Cl, and CHBr₃ concentrations showed significant differences between summer 2008 and spring 2009. The sea-to-air fluxes calculated using the equation of Liss and Merlivat (In: Buat-Menard P (ed) The role of air-sea exchange in geochemical cycling, 1986) indicated that the SYS was a source of CHCl₃ and C₂HCl₃ to the atmosphere during the investigation period.     

中国东海二甲基巯基丙酸内盐(DMSP)合成与降解菌的水平和垂直分布

【目的】二甲基巯基丙酸内盐(dimethylsulfoniopropionate,DMSP)及其裂解产物二甲基硫(dimethyl sulfide,DMS)在海洋硫循环中发挥重要作用。目前关于DMSP降解细菌的分布已有部分报道,但其合成细菌的研究才刚刚起步。本文拟研究中国东海水体DMSP合成与降解菌及基因的水平和垂直分布(1000m水深)差异,分析其对环境梯度变化的响应。【方法】利用流式细胞仪计数海水样品中微微型浮游生物的数量,通过荧光定量PCR和高通量测序手段定量测定DMSP合成基因(dsy B和mmt N)及物种、DMSP降解基因(ddd P和dmd A)及物种的丰度,分析其在东海海域水平及垂直方向上的分布差异。【结果】在垂直方向上,聚球藻、原绿球藻、微微型真核生物和异养细菌丰度随着水深的增加而先增后减,最大值位于30–50m附近。表层(4m左右)水体的DMSP合成及降解基因丰度最高,DMSP合成菌(如Alteromonas、Phaeobacter和Pelagibaca等)丰度也最高;随着水深增加,表层以下水体中DMSP合成及降解基因和物种丰度先增加后降低,峰值均出现在100–150 m;100 m以下,DMSP降解基因丰度迅速下降,而合成基因丰度下降程度较低,而且接近底层(500 m)时出现随水深逐渐增加的趋势。水平方向二者变化规律不明显。浅层水体(≤100 m)和深层水体(100 m)细菌群落结构存在显著差异,前者拥有较高比例的黄杆菌纲、放线菌纲和蓝细菌纲细菌,后者α变形菌纲细菌丰度较高。【结论】100m及以浅和100m以深的浮游细菌群落结构存在显著差异。表层水体中DMSP合成和降解细菌的丰度最高,100–150 m水体次之,但100–1022 m介导的DMSP合成和降解细菌丰度的变化趋势有较大差别。     

高分辨率熔解曲线法的非标记探针基因分型技术

PCR反应中利用荧光检测技术对已知位点进行基因分型时常采用荧光标记的寡核苷酸做探针。近年来新兴起的高分辨率熔解曲线技术可以采用非标记的探针对已知位点的SNP(single nucleotide polymorphism)或突变进行基因分型研究。采用非标记探针法对已知位点的基因分型研究具有廉价、快速、简便等特点,因此被大量应用在和疾病、形状等相关的一些多肽位点的研究中。本文较详细地介绍该技术的基本原理和实验中的注意事项。     

Reductive Reactivity of Iron(III) Oxides in the East China Sea Sediments: Characterization by Selective Extraction and Kinetic Dissolution

Reactive Fe(III) oxides in gravity-core sediments collected from the East China Sea inner shelf were quantified by using three selective extractions (acidic hydroxylamine, acidic oxalate, bicarbonate-citrate buffered sodium dithionite). Also the reactivity of Fe(III) oxides in the sediments was characterized by kinetic dissolution using ascorbic acid as reductant at pH 3.0 and 7.5 in combination with the reactive continuum model. Three parameters derived from the kinetic method: m ₀ (theoretical initial amount of ascorbate-reducible Fe(III) oxides), k′ (rate constant) and γ (heterogeneity of reactivity), enable a quantitative characterization of Fe(III) oxide reactivity in a standardized way. Amorphous Fe(III) oxides quantified by acidic hydroxylamine extraction were quickly consumed in the uppermost layer during early diagenesis but were not depleted over the upper 100 cm depth. The total amounts of amorphous and poorly crystalline Fe(III) oxides are highly available for efficient buffering of dissolved sulfide. As indicated by the m ₀, k′ and γ, the surface sediments always have the maximum content, reactivity and heterogeneity of reactive Fe(III) oxides, while the three parameters simultaneously downcore decrease, much more quickly in the upper layer than at depth. Albeit being within a small range (within one order of magnitude) of the initial rates among sediments at different depths, incongruent dissolution could result in huge discrepancies of the later dissolution rates due to differentiating heterogeneity, which cannot be revealed by selective extraction. A strong linear correlation of the m ₀ at pH 3.0 with the dithionite-extractable Fe(III) suggests that the m ₀ may represent Fe(III) oxide assemblages spanning amorphous and crystalline Fe(III) oxides. Maximum microbially available Fe(III) predicted by the m ₀ at pH 7.5 may include both amorphous and a fraction of other less reactive Fe(III) phases.     

Spatial distributions of dimethyl sulfur compounds,DMSP-lyase activity,and phytoplankton community in the East China Sea during fall

The spatial distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), DMSP-lyase activity (DLA) and their controlling factors including nutrients, phytoplankton community and bacterial abundance were investigated in the East China Sea (ECS) during fall from October 19 to November 2, 2015. Diatoms and dinoflagellates dominated the phytoplankton community, while other taxonomic groups were rare and mainly found in the oligotrophic open sea. Affected by the high nutrients concentrations, Chl a, DMS, DMSP and DLA showed high values in eutrophic inshore waters, and decreased from the costal zones to the open sea. Statistical analysis suggested that diatoms and dinoflagellates were the main controlling factors of DMS, DMSP, and DLA in ECS. For size-fractionated samples, a reduced contribution of the microplankton from inshore stations to offshore stations affected by the trophic conditions was noted. Meanwhile, this decrease in microplankton led to an increase in the ratio of DLA contributed by picoplankton and free-living bacteria from the estuary area to the offshore region. The DMS sea-to-air flux was calculated using the equation of Nightingale et al. (Glob Biogeochem Cy 14(1):373–387, 2000), and approximately 2.88 × 10^?2 Tg of sulfur was transferred from the sea into the atmosphere in the form of DMS in ECS during fall.     

Experimental evidence for long-term coexistence of copiotrophic and oligotrophic bacteria in pelagic surface seawater

Most marine copiotrophic bacteria can produce extracellular enzymes to degrade biopolymers into bio-available smaller solutes, while oligotrophic bacteria usually cannot. Bacterial extracellular enzymes and enzymatic products can be a common resource that could be utilized by both copiotrophs and oligotrophs; when present, oligotrophs may outcompete the enzyme-producing copiotrophs. However, copiotrophs and oligotrophs consistently coexist in the ocean. How they maintain coexistence has still not been experimentally studied. In this study, the interaction and coexistence of a copiotroph and an oligotroph, isolated from the same surface seawater sample and utilizing the same proteinaceous substrate, were experimentally investigated. The copiotroph could secrete extracellular proteases to degrade and then utilize the proteinaceous substrate. The oligotroph was unable to utilize the proteinaceous substrate by itself, but could grow by using the hydrolysate amino acids. The copiotroph outcompeted the oligotroph by adsorbing the amino acids quickly and having a higher growth rate in the rich medium. The oligotroph survived by adapting to low concentration of nutrients. The copiotroph and oligotroph were able to maintain long-term (up to 142 days) coexistence in the laboratory. This study indicates that differences in the utilization of different concentrations of nutrients can drive the coexistence of marine copiotrophs and oligotrophs.     

S-Nitrosylation of Akt by organic nitrate delays revascularization and the recovery of cardiac function in mice following myocardial infarction

The effects of long-term nitrate therapy are compromised due to protein S-Nitrosylation, which is mediated by nitric oxide (NO). This study is to determine the role of Akt S-Nitrosylation in the recovery of heart functions after ischaemia. In recombinant Akt protein and in HEK293 cells, NO donor decreased Akt activity and induced Akt S-Nitrosylation, but was abolished if Akt protein was mutated by replacing cysteine 296/344 with alanine (Akt-C296/344A). In endothelial cells, NO induced Akt S-Nitrosylation, reduced Akt activity and damaged multiple cellular functions including proliferation, migration and tube formation. These alterations were ablated if cells expressed Akt-C296/344A mutant. In Apoe^−/− mice, nitroglycerine infusion increased both Akt S-Nitrosylation and infarct size, reduced Akt activity and capillary density, and delayed the recovery of cardiac function in ischaemic hearts, compared with mice infused with vehicle. Importantly, these in vivo effects of nitroglycerine in Apoe^−/− mice were remarkably prevented by adenovirus-mediated enforced expression of Akt-C296/344A mutant. In conclusion, long-term usage of organic nitrate may inactivate Akt to delay ischaemia-induced revascularization and the recovery of cardiac function through NO-mediated S-Nitrosylation.