海洋硅藻硅质细胞壁结构的形成机理研究概述

硅藻具有形态各异、结构复杂、精美绝伦的硅质细胞壁,是海洋中进行生物硅化最主要的生物体。硅质细胞壁的形成同样是一个错综复杂的过程,它涉及硅藻细胞将硅酸从胞外转运到胞内;硅酸在细胞内的转移;在硅沉积囊泡(SDV)中的浓缩沉积;最后合成具种类特异性的细胞壁。重点介绍硅酸转运基因(SITs)的分子特征与作用机制;与生物硅化相关的三种蛋白即硅体蛋白(frus-tulins)、亲硅蛋白(silaffins)和侧壁蛋白(pleuralins)的结构与功能;硅质结构如何在硅沉积囊泡内最终形成的模式。     

Fronts and surface zonal geostrophic current along 115°E in the southern Indian Ocean

硅藻具有形态各异、结构复杂、精美绝伦的硅质细胞壁,是海洋中进行生物硅化最主要的生物体。硅质细胞壁的形成同样是一个错综复杂的过程,它涉及硅藻细胞将硅酸从胞外转运到胞内;硅酸在细胞内的转移;在硅沉积囊泡(SDV)中的浓缩沉积;最后合成具种类特异性的细胞壁。重点介绍硅酸转运基因(SITs)的分子特征与作用机制;与生物硅化相关的三种蛋白即硅体蛋白(frustulins)、亲硅蛋白(silaffins)和侧壁蛋白(pleuralins)的结构与功能;硅质结构如何在硅沉积囊泡内最终形成的模式。     

硅藻硅酸盐转运子(silicate transporter, SIT)研究进展

硅藻是海洋浮游植物主要类群和海洋生态系统的重要初级生产者,其硅质壁的存在使其成为了海洋生物硅的最大贡献者,而且成为海洋碳汇的主要来源。因此,硅质壁形成机制的阐明至关重要。硅酸盐转运是硅藻硅质壁形成中的关键,阐明其转运机制对建立硅藻代谢途径模型和进一步理解硅藻在海洋生态系统及生物地球化学循环中的作用具有重大意义。硅酸盐转运子(silicate transporter,SIT)是硅藻中参与硅吸收或转运的一类膜蛋白,因其重要性及多样性成为讨论及研究的焦点。本文综述了硅藻中SIT的分子特征、分子机制、功能多样性及进化关系,为SIT转运机制的研究提供了理论基础。     

硅藻硅酸转运子（silicon transporters, SITs）研究进展

硅藻是海洋浮游植物主要类群和海洋生态系统的重要初级生产者，其硅质壁的存在使其成为了海洋生物硅的最大贡献者，而且成为海洋碳汇的主要来源。因此，硅质壁形成机制的阐明至关重要。硅酸转运是硅藻硅质壁形成中的关键，阐明其转运机制对建立硅藻代谢途径模型和进一步理解硅藻在海洋生态系统及生物地球化学循环中的作用具有重大意义。硅酸转运子(silicon transporters, SITs)是硅藻中参与硅吸收或转运的一类膜蛋白，因其重要性及多样性成为讨论及研究的焦点。本文综述了硅藻中SITs的分子特征、分子机制、功能多样性及进化关系，为SITs转运机制的研究提供了理论基础。     

楚科奇海与白令海表层沉积中的钙质和硅质微体化石研究

通过对北冰洋楚科奇海和令海41个表层沉积样品中的有孔虫、介形类等钙质微体化石和硅藻、放射虫、海绵骨针等硅质微体化石的定量分析，发现表层沉积中浮游有孔虫几乎缺失，这可能与该区表层生产力相对低、碳酸盐溶解作用较强有关，而底栖有孔虫和硅质微体化石的丰度分布则明显受表层沉积物类型、表层初级生物生产力和碳酸盐溶解作用所控制。其中，北冰洋楚科奇海陆架区有孔虫丰度和分异度低，含少量浅水介形类，放射虫在陆架浅水区缺失，但含有较多硅藻和海绵骨针等其它硅质微体化石，反映该区由于海冰、表层海水温度较冷而导致表歧初级生产力相对低。白令海陆坡区底栖有孔虫丰度比较科奇海高一个数量级，底栖有孔虫分异度也相对高，硅藻、放射虫、海绵骨针等硅质微体化石的丰度与钙质化石一样，其丰度比楚科奇海明显高，反映表层初级生产力相对高。根据白令海陆坡区底栖有孔虫和硅质微体化石丰度、底栖有孔虫胶结质壳比值的水深变化，推测该区碳酸盐溶跃层和补偿深度（CCD）相对浅，分别位于水深2000m和3800m处。     

硅藻硅质化蛋白——亲硅蛋白(silaffins)

硅藻是一类在全世界水环境中都有发现的单细胞真核藻类,其特有的硅质壁使其成为海洋生物硅的最大贡献者,它们在全球碳/硅元素的生物地球化学循环中扮演至关重要的角色。亲硅蛋白(silaffins)是一种分离于硅藻硅质壁,并与其硅质化密切相关的蛋白。亲硅蛋白可以在体外硅酸溶液中沉淀二氧化硅(SiO_2),这种活性来自其特有的蛋白序列和翻译后修饰调节。基于对亲硅蛋白结构的理解,多种与其相似的仿生多肽被应用到人工SiO_2的合成中。本文综述了硅藻亲硅蛋白的分离鉴定、功能以及其在生物技术和生物医药方面的应用,为亲硅蛋白基础研究和应用潜力提供基础。     

海水中可溶性无机硅

海水中可溶性无机硅(以下简称硅),是海洋浮游植物所必须的营养盐之一,尤其是对硅藻类浮游植物、放射虫和硅质海绵,硅更是构成机体不可缺少的组分。在海洋浮游植物中硅藻占很大部分,硅藻繁殖时摄取硅使海水中硅的含量下降。浮游植物死亡下沉分解又释放出硅,使海水中硅的含量再生。另外放射虫也能排泄出二氧化硅,硅质死亡迅速释放二氧化硅进入海水中。总之硅的含量对于海洋生物产量具有直接和间     

第五节 海水中可溶性无机硅

海水巾可溶性无机硅(以下简称硅)，是海洋浮游植物所必须的营养盐之一，尤其是对硅藻类浮游植物、放射虫和硅质海绵，硅更是构成机体不可缺少的组分。在海洋浮游植物中硅藻占很大部分，硅藻繁殖时摄取硅使海水中硅的含量下降。浮游植物死亡下沉分解又释放出硅，使海水中硅的含量再生。另外放射虫也能排泄出二氧化硅，硅质死亡迅速释放二氧化硅进入海水中。总之硅的含量对于海洋生物产量具有直接和间接影响，由此可知生物活动使海水中硅的含量随季节呈现周期性变化。     

西太平洋E20岩芯末次冰期以来的沉积特征与环境意义

硅藻席沉积在热带西太平洋陆续被发现,其形成年代和机制对于热带西太平洋碳循环研究具有重要意义。本文对采自西马里亚纳弧,含近2.5 m厚硅藻席沉积的E20岩芯进行了高分辨率的XRF元素扫描、颜色扫描以及AMS14C测年分析。结果表明,E20可分为3个沉积单元,从下至上具有深海黏土—硅质软泥—硅质黏土的沉积序列,Ti、Fe、Cu、Br等元素呈三段式变化,Ca与Si元素呈反向变化。综合AMS14C测年结果推测,E20反映了西太平洋低纬度海区末次冰期以来显著的环境变化,10.9～28.6 ka B.P.为硅藻席勃发期,而末次冰期时风尘输入量的增加可能是勃发的主要原因。硅藻席沉积的保存与其周围的围陷地形有很大关系。     

低盐度形成的微生物膜对厚壳贻贝稚贝附着的影响

为研究环境因子在厚壳贻贝(Mytilus coruscus)稚贝附着过程中的调控作用, 作者探讨了低盐度对微生物膜生物构成、群落结构的影响及所形成微生物膜对厚壳贻贝稚贝附着的影响。在实验室条件下, 研究微生物膜的日龄与干质量、细菌密度和硅藻密度、叶绿素a含量的关系及其对厚壳贻贝稚贝附着的影响。通过DGGE指纹图谱技术对微生物膜中的细菌群落结构多样性进行了分析。研究发现,盐度13和23时形成的微生物膜能有效促进厚壳贻贝稚贝的附着, 且盐度23、28d时稚贝附着率最高, 达到72%。相关性分析表明, 微生物膜的诱导活性与盐度、干质量、细菌密度、硅藻密度、日龄呈显著正相关性, 与叶绿素a无相关性。微生物膜的干质量、附着细菌密度及底栖硅藻密度明显随着日龄的增加而增加, 叶绿素a含量与微生物膜日龄无显著相关性。细菌群落在厚壳贻贝稚贝附着过程中发挥重要调控作用。     

The use of soft X-ray spectromicroscopy to investigate the distribution and composition of organic matter in a diatom frustule and a biomimetic analog

Diatoms play a significant role in the global carbon cycle through their role in biogenic silica production and the transport of organic matter to the seafloor. Recent work has shown that silicified diatom frustules contain a significant amount of organic matter, and that the proportion of diatom-bound organic matter increases with depth in the water column and sediments. Here, we investigate the association between organic matter and the mineral phase. We used a combination of scanning transmission X-ray microscopy (STXM) and carbon X-ray absorption near-edge structure (XANES) spectroscopy to characterize the distribution and composition of organic matter in frustules of the diatom Cylindrotheca closterium and a biomimetic silica gel. To our knowledge, this study represents the first successful attempt to simultaneously image and obtain chemical information about the organic matter within a diatom frustule using X-ray spectromicroscopy near the carbon edge. Organic carbon, most likely protein, was distributed throughout the frustules and was not removed by harsh chemical treatment. The physical structure of the frustules appeared to be related to the chemical composition of this organic matter, with aromatic or unsaturated carbon being concentrated in the most intricately patterned regions of the frustule. A similar physical and chemical structure was observed in a biomimetic silica gel precipitated spontaneously with polylysine. These results are consistent with the theory that organic constituents of diatom frustules direct silica precipitation and become incorporated within the silica matrix as it forms. The relationship between organic matter composition and silica morphology, the failure of harsh chemical treatments to remove this organic matter, and the spontaneous nature of the co-precipitation of silica and organic matter indicate some chemical interaction between the siliceous and organic components of diatom frustules. Frustule-bound organic matter should therefore be protected from decomposition in the water column or diagenetic alteration in sediments unless the frustule dissolves.     

Observations of resuspended diatoms in the turbid tidal edge

Observations of resuspended diatoms in the shallow waters (<60 cm) of the turbid tidal edge are described for single sites on two tidal flats–the Molenplaat in the Westerschelde estuary, and the Hond in the Ems-Dollard estuary, The Netherlands. High concentrations of chlorophyll-a (chl-a) were observed in the trailing edge of the ebbing tide in water depths of <20 cm, after which concentrations decreased markedly. Peak mean values were 19 μg chl-a l⁻¹ in 10 cm of water at the Molenplaat, and 45 μg chl-a l⁻¹ in 5 cm of water at the Hond. Similar trends were observed on the flooding tide, although peak values were far less pronounced (6 and 30 μg chl-a l⁻¹ respectively). Microscopic examination of the diatom community within the turbid tidal edge at the Molenplaat revealed that peaks in biomass were caused by suspended benthic diatoms, as well as the large centric diatom Coscinodiscus sp., particularly on the ebb tide. Planktonic diatoms other than Coscinodiscus sp. were more randomly distributed and did not appear to follow any particular trend. It would seem that as the tide recedes, resuspended benthic diatoms and large Coscinodiscus sp. cells become concentrated in the shallow water. However, the virtual absence of Coscinodiscus sp. from the leading edge of the flooding tide suggests that most of the resuspended cells do not settle to the seabed, but are washed away into the channels. The small peak of benthic diatoms at the leading edge of the flood tide is most likely resuspended locally from the sediment, along with large numbers of diatom frustules.     

Biological controls on dissolution of diatom frustules during their descent to the deep ocean: Lessons learned from controlled laboratory experiments

The majority of opal produced by diatoms dissolves during their sedimentation to the seafloor, but spatial and temporal variability of dissolution rates are large. Controlled laboratory experiments using live phytoplankton or phyto-detritus may help identify the different processes, including those that are biologically mediated or physico-chemically driven, that impact the dissolution of frustules and the aforementioned variability. Results of eight bSiO₂ dissolution experiments, seven of which were conducted at low temperatures (<6 °C) are presented within the context of earlier similar studies, and different phases of dissolution dynamics characterized. TEP concentration, aggregation and the physiological status of the diatoms determined the period during which diatoms may maintain the protective membrane that surrounds their frustule and effectively reduces or completely inhibits (lag period) dissolution for some time. Once diatoms loose the capability to maintain their protective membrane, bacterial activity compromises it. Physico-chemical dissolution, which depends on frustule structure and abiotic environmental conditions, begins once the protective membrane is damaged. The ability of diatoms to maintain their membrane, the bacterial composition and activity governing its degradation, and the physico-chemical dissolution dynamics of exposed frustules are all impacted by temperature. In our experiments instantaneous dissolution rates were not dependant on bSiO₂ concentration at low temperatures, although such a relationship was observed under otherwise identical conditions at 15 °C, implying that biotic factors rather than physico-chemical processes initially dominated dissolution at polar temperatures. Since inhibition of bSiO₂ dissolution at low temperatures was inhibited to a greater extent than organic matter degradation, we postulate that it was not reduced bacterial activity but the enhanced ability of diatoms to maintain their membrane and thus withstand microbial attack that caused the low initial dissolution rates at <6 °C. In situ, interactions between the different biotic and abiotic processes impacting dissolution combined with differences in sinking velocity of diatom aggregates and grazing effects could easily explain high spatial and temporal variability in the accumulation of diatoms on the seafloor. Simple calculations based on our experimental results suggest that Fragilariopsis kerguelensis, for example, would be appreciably more likely to reach the seafloor than Chaetoceros debilis if both grow at low growth rates, e.g. under growth limiting conditions. However, dissolution behavior of Chaetoceros debilis during sedimentation may differ under conditions where this species forms large blooms.     

不同藻类生态参数在反演沉积物环境中的应用比较

海洋沉积物中残留的硅壳、甲藻孢囊、类脂类化合物及生物硅等生态参数被广泛应用于反演和指示海洋古环境特征.本研究通过测定烟台四十里湾表层沉积物中的硅藻化石、甲藻孢囊、菜籽甾醇、甲藻甾醇及生物硅5种生态参数,比较不同生态参数的相关性及它们在反演海洋环境中的功能差异,建立了多参数综合应用的研究方法.研究发现,沉积物中的硅壳丰度与菜籽甾醇含量及生物硅含量存在明显正相关关系(P＜0.05),菜籽甾醇含量与生物硅含量可以较好的佐证与提高沉积物中硅壳对硅藻生物量指示的准确性;甲藻孢囊与甲藻甾醇含量相关性不明显(P＞0.05),相较而言,甲藻甾醇可以更准确的反演甲藻的生物量.因此,生物与化学参数的结合应用不仅可以提高生物量指示的精确性,而且有助于从物种组成角度更好的了解藻类对环境变化的响应特征.     

Dietary Preferences and Carbon Absorption by two Grazing Gastropods, G/bbula umbilicaris (LINNÉ) and Jujubinus striatus (LINNÉ)

Abstract. Ingestion rates and absorption efficiencies in Gibbula umbilicaris and Jujubinus striatus feeding on green algal films, diatoms, macro-epiphytes, and dead Posidonia ocean/'ca-Ieaves have been investigated in laboratory experiments.
For both gastropod species, ingestion rates were highest in diatoms and thin green algal films as food source. G. umbilicaris exhibited significant lower consumption rates when feeding on seagrass debris or macro-epiphytes, J. striatus consumed neither Posidonia-debris nor macro-epiphytes.
Highest carbon absorption efficiencies were found in both gastropod species when feeding on diatoms and green algal films. Significantly lower efficiencies were found in G. umbilicaris when consuming seagrass debris or macro-epiphytes.
Analyses of fecal material confirmed these findings. Highest organic carbon contents were measured in fecal pellets produced after consumption of seagrass debris or macro-epiphytes reflecting the presence of structural carbohydrates. SEM examinations of feces revealed mainly diatom frustules, refractory parts of macroalgal and other plant material. Analyses of gut contents gave similar results suggesting a basically microphagous herbivory for both gastropod species.
Since seagrass debris and macro-epiphytes are not used very effectively, the high absorption efficiencies when animals feed on the microfloral component of the periphyton are discussed as possible adaptation to limited food availability.     

Variations of antioxidant efficiency and presence of endosymbiotic diatoms in the Antarctic porifera Haliclona dancoi

The role of endosymbiotic diatoms as pro-oxidant stressors in porifera has been investigated in the Antarctic sponge Haliclona dancoi in which the presence of diatoms is influenced by marked seasonal variations during the austral summer. Both chlorophaeopigments and frustules were absent in sponge tissues sampled in early November at the beginning of the summer and increased from the mid of December with slightly shifted temporal trends. The efficiency of antioxidant defenses in the sponge showed a marked response to symbionts with clearly enhanced values corresponding to the peak of diatoms.     

Variations of antioxidant efficiency and presence of endosymbiotic diatoms in the Antarctic porifera Haliclona dancoi

The role of endosymbiotic diatoms as pro-oxidant stressors in porifera has been investigated in the Antarctic sponge Haliclona dancoi in which the presence of diatoms is influenced by marked seasonal variations during the austral summer. Both chlorophaeopigments and frustules were absent in sponge tissues sampled in early November at the beginning of the summer and increased from the mid of December with slightly shifted temporal trends. The efficiency of antioxidant defenses in the sponge showed a marked response to symbionts with clearly enhanced values corresponding to the peak of diatoms.     

Seasonal trends in the pigment and amino acid compositions of sinking particles in biogenic CaCO3 and SiO2 dominated regions of the Pacific sector of the Southern Ocean along 170°W

We investigated amino acids and pigments in particles settling through the water column of the Southern Ocean and showed that spatial and temporal differences in phytoplankton source and consumer population influence sinking particle composition. Sediment traps were deployed along 170°W from November 1996 to March 1998 as part of the United States Joint Global Ocean Flux Study (US JGOFS) Antarctic Environment Southern Ocean Process Study (AESOPS) program. Peak fluxes of amino acids and pigments occurred during austral spring and summer (November–April) and were highest in the Antarctic Circumpolar Current (ACC). Compositional changes in pigments and total hydrolyzed amino acids demonstrate how the source of sinking particles varies with latitude and suggest that sinking material was most degraded in relatively diatom-depleted regions and toward the end of the high-flux period (February–March). At the Subantarctic Front, high proportions of pheophytin and β-alanine illustrate the important role of microbes in degradation. Further south at the Antarctic Polar Front, glycine, pyropheophorbide, and pheophorbide enrichments reflected a greater contribution of diatoms and greater processing by zooplankton grazers. Even further south in the ACC, enrichments of the diatom pigment fucoxanthin, diatom cell wall indicators glycine and serine, and diatom frustule-bound amino acids suggested the settling of empty frustules and aggregates. Despite being protected by the mineral, diatom-bound amino acids were not preferentially preserved between shallow and deep traps, possibly because of silica dissolution and a relatively small amount of organic carbon remineralization. Our results show that organic matter at diatom-rich stations is removed by mechanisms that do not result in the appearance of organic matter degradation indicators. Recent observations that calcium carbonate has a higher carrying capacity for sinking organic matter than silica may be related to diatom silicification, physiological status and decomposition pathway.     

The occurrence of ‘epipsammic’ diatom populations: A result of interaction between physical sorting of sediment and certain properties of diatom species

The role of ‘sand’ (particles >55 μm) as a substratum for benthic diatoms was investigated, using sediments collected from tidal flats and main channels in the Ems estuary. On average, 13% of the sand grains were occupied by one or more diatom cells. It appeared that 80% of the diatom cells in this fraction were present in or on mud coating the sand grains. Of the sand grains in the water, 7% were occupied by diatom cells. The preference of benthic diatoms for the mud coatings rather than the bare parts of the sand grains stresses the importance of ‘mud’ (particles <55 μm) as a substratum for diatoms on the tidal flats. This was confirmed by separate cell counts for the mud and sand fractions.Of the sand grains with attached diatoms, the mean number of diatom cells per grain in the water was similar to that on the tidal flats. This indicates a large exchange of sand between tidal flats and channels. A similar exchange between tidal flats and possibly a shift in the species composition. These processes suggested by the striking similarities in cell number distribution and species composition in samples from these two habitats. However, on exposed tidal flats certain species were present in lower numbers than in the channels, indicating that loosely attached diatoms can be scoured off their substratum. Consequently, two factors are assumed to contribute to the dynamics of the species composition of benthic diatoms. The first is the adhesion capacity of diatoms and the second is sediment sorting by currents and waves. These factors cause a differential but significant flux of benthic diatoms to and from the channels, followed by changes over time in the diatom populations on the tidal flats and possibility a shift in the species composition. These processes show that the terms ‘epipelic’ and ‘epipsammic’ are not helpful to classify the main components of the diatom flora in this estuary.     

我国典型潮间带底栖硅藻群落空间分布特征

底栖硅藻是河口、泥质海滩生态系统的重要生物类群,其数量与分布变化直接或间接地影响到多种海洋生物的饵料供给、海鸟的生存与迁徙。通过对我国从南到北14个典型潮间带表层沉积物中底栖硅藻的分析,共鉴定出硅藻153种,其物种多样性（Shannon-Weaver 指数范围:1.61~4.39）与生物量（范围:0.09×103 ~ 10×103个/g,干质量）在空间上存在显著差异;聚类分析与相似性分析检验（r=0.738,P=0.1%< 0.01）表明,14个调查区域的硅藻群落在空间上可分为4个大的组合,分别对应着渤、黄、东、南海4个区域,吻合了我国近海浮游植物的地理分布特征。与环境因素的相关性分析表明,底栖硅藻群落的物种多样性与生物量受沉积物类型与盐度的影响显著,泥质区域更有利于硅藻的保存,而生物多样性在泥砂质低盐区域相对较高。此外,底栖硅藻生物量与表层沉积物中TOC含量表现出显著正相关性;δ13C数值的空间变化范围为-25‰~-20‰,指示了有机质陆海混合的特征,其中,涧河河口、黄河口、大沽河口、苏北浅滩区域,δ13C数值明显偏正,表明底栖硅藻可能是这些区域沉积物中有机碳的重要贡献者。