凡纳滨对虾低盐度高产虾池环境微生物生态研究

对广东珠三角地区,凡纳滨对虾低盐度高产虾池环境微生物调查结果,养殖水体异养菌平均数量为5.15×104cfu·mL-1,致病性弧菌为5.00×103cfu·mL-1,池底泥浆中异养细菌平均数量为2.41×106cfu·mL-1,致病性弧菌为1.45×105cfu·mL-1。不同虾池异养细菌的数量差别小而稳定,致病性弧菌的数量差别及波动大。淤泥较深的老化虾池,水体和泥浆中异养细菌平均分别为6.10×104cfu·mL-1和2.89×106cfu·mL-1,致病性弧菌为6.00×103cfu·mL-1和2.14×105cfu·mL-1;无淤泥虾池水体和泥浆中异养细菌平均分别为4.53×104cfu·mL-1和2.08×106cfu·mL-1,致病性弧菌为4.34×103cfu·mL-1和9.86×104cfu·mL-1。老化虾池底泥致病性弧菌明显偏高,成为老化虾池易爆发虾病的重要原因。低盐度虾池水体异养菌和致病性弧菌的数量变化,表现为养殖前期高,中后期低而稳定;池底泥浆中异养菌和致病性弧菌的数量变化,呈不规则波动。高的养殖水温对养殖环境异养菌和致病性弧菌表现抑制作用,养殖环境微生物与水体浮游藻类也有一定的关系。     

巨桉人工林地土壤微生物类群的生态分布规律

研究了四川省洪雅县巨桉人工林地土壤微生物数量及其类群分布规律.结果表明,洪雅县巨桉人工林地土壤微生物数量具有明显的季节变化,各样地均以秋季最多,达到17.42×10⁶ CFU·g^-1,春季次之,夏季最少.土壤微生物主要集中在0～20 cm的土层,随着土层的加深,微生物数量迅速减少;在0～60 cm土层,同一类群微生物数量变动范围较大,其中好气性细菌0.31×10 ⁶～14.39×10⁶ CFU·g^-1,放线菌0.06×10 ⁶～0.79×10⁶ CFU·g^-1,真菌0.02×10 ⁶～0.07×10 ⁶ CFU·g^-1,厌氧细菌0.05×106～3.22×106 CFU·g^-1.巨桉人工林地微生物以细菌为主要类群,占微生物总数的92.83%以上,其次是放线菌和真菌,其微生物组成结构合理.与青冈次生林和农耕地相比,巨桉人工林地微生物数量远远高于青冈次生林地,有利于土壤微生物生长.细菌生理类群的Simpson多样性指数和Shannon-Wiener多样性指数分别达到0.773和1.896.     

鱼虾混养生态系中细菌动态变化的研究

中国对虾和黑鲷混养生态系中几种主要细菌的动态变化研究结果表明 ,养殖初期 ,鱼虾混养池水体中异养菌总量和硝酸盐还原菌数量较低 ,但高于对照的对虾单养池 .随着养殖时间的推移 ,对照池的两种菌的菌量急剧增加 ,8、9月份菌量仍维持在较高水平 ;而混养池的菌量在高温季节虽有增加 ,但仍保持在 10 4 cells·ml-1范围内 ,增长幅度远远低于对照池 ,且 9月底开始下降 .底泥中的细菌数量与水体中细菌有相似的变化规律 ,但一般高于同期水中菌量 1～ 2个数量级 .混养池中的弧菌数量一直低于同期对照池 .可见 ,鱼虾混养可通过对养殖生态系中细菌的激活和调节作用 ,调节生态系统的物质循环 ,使其保持高速、稳定运行 ,为对虾生长提供一个健康而稳定的环境 ,同时增加综合养殖效益     

食物浓度对角突臂尾轮虫种群增长、个体大小和卵大小的影响

以蛋白核小球藻为食物 ,应用群体累积培养法研究了食物浓度对角突臂尾轮虫种群增长、个体大小和卵大小等的影响 .结果表明 ,食物浓度对角突臂尾轮虫种群增长率、个体大小和卵大小均有极显著影响 .其中 ,轮虫种群增长率与食物浓度间呈曲线相关 ;当食物浓度为 8.2 4 5 3× 10 6cells·ml-1时 ,种群增长率达最大值 0 .6 0 85d-1;在所研究的食物浓度范围内 ,轮虫个体具有随食物浓度的增大而增大的趋势 ,轮虫卵体积在中等食物浓度范围 (6 .0× 10 6～ 9.0× 10 6cells·ml-1)时较大     

食物密度对镜湖萼花臂尾轮虫不同克隆生活史特征的影响

对镜湖萼花臂尾轮虫（Brachionus calyciflorus）夏季种群内4个生化遗传特征上互不相同的克隆（克隆A、B、C和D）在4个斜生栅藻（Scenedesmus obliquus）密度（1.0×10⁶、2.0×10⁶、4.0×10⁶和8.0×10⁶ cells·L^-1）下的生活史特征进行了研究.结果表明：食物密度对各克隆轮虫的存活率和繁殖率均有不同的影响.4克隆中克隆C的世代时间最短,克隆B的世代时间、生命期望和平均寿命最长,克隆A的后代混交雌体百分率最高;净生殖率和个体适合度在4克隆间无显著差异.镜湖萼花臂尾轮虫在2.0×10⁶ cells·L^-1的食物密度下净生殖率最低;在1.0×10⁶cells·L^-1的食物密度下平均寿命和生命期望最短,而后代混交雌体百分率却最高;在8.0×10⁶cells·L^-1的食物密度下种群内禀增长率最高,平均寿命和生命期望最长;在高食物密度（4.0、8.0×10⁶cells·L^-1）下个体适合度较大.克隆C的个体适合度在密度为3.9×10⁶cells·L^-1时最小,而克隆D的个体适合度在食物密度为6.34×10⁶cells·L^-1时最大.食物密度的变化可能是7月份之后镜湖萼花臂尾轮虫从水环境中消失的原因,而4克隆轮虫个体适合度的相似性则可能是镜湖轮虫共存于同一水体的原因之一.     

黄河上游玛曲段春季浮游生物群落结构特征

为了了解黄河上游玛曲段的水质状况,于2006年4—5月对黄河玛曲段干流浮游生物的群落组成进行了调查。结果表明：全段的浮游植物共有5门23种（属）,浮游植物密度为3.2×10⁴～54×10⁴ cells·L^-1,平均密度为19.7×10⁴ cells·L^-1,生物量为0.069～0.464 mg·L^-1,平均生物量为0.228 mg·L^-1,其中密度最高的为齐哈玛,生物量最高的为玛曲大桥;浮游动物共有2门10种（属）,密度为670～1273 cells·L^-1,平均为881.56 cells·L^-1,生物量为0.044～0.089 mg·L^-1,平均为0.064 mg·L^-1;该河段浮游生物组成多以冷水性为主;浮游植物多样性指数介于2～3,表明黄河上游玛曲段水质呈轻度污染;浮游生物丰富度与均匀度值均较低,群落结构组成不稳定,易受外界环境的干扰。     

2004年东海原甲藻赤潮爆发的现场调查和分析

2004年4～5月对东海赤潮高发区开展了赤潮原因种的大面观测并对期间爆发的特大赤潮进行跟踪调查,在56个站位采集了171份样品。表层东海原甲藻(Prorocentrumdonghaiense)变化范围为2.5×103～6.0×107cells·L-1,最大值出现在122.94°E,30°N的rb12A站;中层东海原甲藻变化范围为1.0×103～5.32×106cells·L-1,最大值出现在rf40站。从水平分布看,东海原甲藻呈不均匀分布,从垂直分布看,赤潮爆发前原甲藻细胞在水体中层密集,大量增殖后上升到表层,爆发赤潮。     

青岛近海及其临近海域冬季微微型浮游植物的分布

微微型浮游植物（0.2～2.0 μm） 是海水中最小的自养浮游生物, 在世界各海域广泛分布, 并在海洋有机物质循环中起着非常重要的作用.利用荧光显微技术对青岛近海及其邻近海域冬季微微型浮游植物丰度进行了调查,研究了微微型浮游植物的空间变化和昼夜变化的特征, 并分析了微微型浮游植物丰度与环境因子的相关性. 结果显示, 冬季该海域以富含藻红素（Phycoerythrin-rich, PE）的聚球藻(Synechococcus, Syn)细胞占优势,微微型真核藻类（Picoeukaryote, Euk）次之,而富含藻蓝素（Phycocyanin-rich, PC）的聚球藻细胞数量很低, 未发现原绿球藻（Prochlorococcus, Pro）的存在.Syn 的变化范围为8.97×10³～1.95×10⁵ cells·ml^-1, 平均4.67×10⁴ cells·ml^-1; Euk的变化范围为1.95×10²～1.01×10⁴ cells·ml^-1, 平均2.39×10³ cells·ml^-1. Syn丰度在胶南以南海域出现高值区域, 在即墨海域和崂山东南海域出现低值区域. Euk丰度在日照海域出现高值区域; 崂山海域为低值区域; 各水层Syn和Euk丰度均无明显差异(P﹥0.05). 对胶州湾中部连续站4层水体的24 h昼夜连续变化进行观测发现, Syn、Euk丰度都有明显昼夜波动.相关性分析表明： Syn与温度、 电导率呈正相关, 与溶氧浓度呈显著负相关; Euk与盐度和溶氧浓度呈显著负相关. 微微型浮游植物对总浮游植物生物量的贡献约为20％.     

深圳海域养殖牡蛎卫生质量状况(Ⅱ)-农药、微生物及麻痹性贝毒的含量与评价

为了了解深圳海域养殖牡蛎体内的卫生质量状况,我们于2002年1月～2004年2月对该海域养殖牡蛎体内的污染物水平进行了检测,结果显示六六六(BHC)为ND(未检出)～0.100 mg·Kg-1湿重,DDT为0.004～0.255mg·Kg-1湿重,细菌总数为ND～9.3×104 Ind·g-1,大肠菌群为ND～5.6×104 Ind·(100g)-1,PSP为ND～34μg·(100g)-1,副溶血性弧菌沙井和后海的近江牡蛎检测结果为阳性,其余站位未检出.参照GB18406.4-2001<农产品安全质量无公害水产品安全要求>,深圳海域养殖牡蛎的六六六、DDT、细菌总数和PSP完全符合要求,沙井和后海的近江牡蛎副溶血性弧菌超标,所有站位的大肠菌群均存在超标.综合重金属的检测结果发现,所有站位的牡蛎均有多个污染物超标,卫生质量欠佳,珠江口和深圳湾的近江牡蛎较大亚湾和大鹏湾的长牡蛎和褶牡蛎卫生质量更差.     

微生态制剂改善对虾养殖池塘底质的效果

研究了在117 d的养殖周期中微生态制剂对南美白对虾池塘底质的改良效果.结果表明,与对照组相比,施用微生态制剂可使底质中总氮、总磷和硫化物的含量显著下降;总菌数量无显著变化,而芽孢杆菌、氨化细菌以及硫氧化细菌、硫还原细菌、弧菌数量差异显著,其中弧菌数量在施用微生态制剂处理和对照条件下分别为3.65×10³ cfu·g^-1和1.16×10⁵ cfu·g^-1.表明施用微生态制剂可以减少氮、磷、硫等营养物质的积累,改善池塘底质的菌相,为南美白对虾的健康养殖提供良好的池塘底质环境.     

Sulfide fluxes in a microbial mat from the Ebro Delta, Spain

The sulfur cycle of Ebro Delta microbial mats was studied in order to determine sulfide production and sulfide consumption. Vertical distribution of two major functional groups involved in the sulfur cycle, anoxygenic phototrophic bacteria and dissimilatory sulfate-reducing bacteria (SRB), was also studied. The former reached up to 2.2×10⁸ cfu cm^–3 sediment in the purple layer, and the latter reached about 1.8×10⁵ SRB cm^–3 sediment in the black layer. From the changes in sulfide concentrations under light-dark cycles it can be inferred that the rate of H₂S production was 6.2 μmol H₂S cm^–3 day^–1 at 2.6 mm, and 7.6 μmol H₂S cm^–3 day^–1 at 6 mm. Furthermore, sulfide consumption was also assessed, determining rates of 0.04, 0.13 and 0.005 mmol l^–1 of sulfide oxidized at depths of 2.6, 3 and 6 mm, respectively. Electronic Publication     

Diversity and vertical distribution of magnetotactic bacteria along chemical gradients in freshwater microcosms

The vertical distribution of magnetotactic bacteria along various physico-chemical gradients in freshwater microcosms was analyzed by a combined approach of viable cell counts, 16S rRNA gene analysis, microsensor profiling and biogeochemical methods. The occurrence of magnetotactic bacteria was restricted to a narrow sediment layer overlapping or closely below the maximum oxygen and nitrate penetration depth. Different species showed different preferences within vertical gradients, but the largest proportion (63-98%) of magnetotactic bacteria was detected within the suboxic zone. In one microcosm the community of magnetotactic bacteria was dominated by one species of a coccoid "Alphaproteobacterium", as detected by denaturing gradient gel electrophoresis in sediment horizons from 1 to 10 mm depth. Maximum numbers of magnetotactic bacteria were up to 1.5 x 10(7) cells/cm3, which corresponded to 1% of the total cell number in the upper sediment layer. The occurrence of magnetotactic bacteria coincided with the availability of significant amounts (6-60 microM) of soluble Fe(II), and in one sample with hydrogen sulfide (up to 40 microM). Although various trends were clearly observed, a strict correlation between the distribution of magnetotactic bacteria and individual geochemical parameters was absent. This is discussed in terms of metabolic adaptation of various strains of magnetotactic bacteria to stratified sediments and diversity of the magnetotactic bacterial communities.     

Detection of ingested bacteria in benthic ciliates using fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) was applied to detect ingested natural bacteria within the food vacuoles of ciliates harvested from the natural sediment. In addition to this important qualitative aspect, FISH was also successfully used to measure the bacterivory of a culture of the ciliate Tetrahymena pyriformis on natural field sediment bacteria. In this feeding experiment, we compared the FISH technique with the only available alternative technique using fluorescently stained sediment (FS-sediment). The ingestion rate of unstained sediment bacteria determined by FISH was 4.6 bacteria per ciliate and hour. In contrast, Tetrahymena pyriformis cells that fed on bacteria from FS-sediment ingested 12.7 bacteria per ciliate and hour. Bacterial abundances in the sediment were equal in both sediment types (4 x 10(8) cells g sediment dry weight(-1)) when determined by DAPI counts. However, when analyzed using DTAF-counts, the number of bacteria in the FS-sediment increased to 9.7 x 10(8) cells g sediment dry weight(-1). From our findings we conclude that bacterivory by ciliates is overestimated when FS-sediment is used because DTAF stains bacteria as well as protein-containing detritus particles, which are also ingested by many ciliates. In contrast, FISH is a direct, a posteriori method that specifically stains phylogenetic lineages, e.g. eubacteria, after ingestion and thereby avoids a false determination of the number of ingested bacteria. Thus this method can also be used for the study of natural ciliate bacterivory in benthic systems.     

长江口低氧区异养细菌及氮磷细菌分布

2009年8月15-28日,对长江口低氧高发海域的异养细菌、无机磷细菌、有机磷细菌、反硝化细菌和氨化细菌的空间分布特征进行初步研究.结果表明:氨化细菌数量最高,表层水、底层水和表层沉积物的数量均值分别为307.52×104个·L-1、184.50×104个·L-1和199.97×102个·g-1;其次为异养细菌,数量均值分别为87.35×104 cfu·L-1、86.85×104cfu·L-1和64.26×102cfu·g-1;再次为有机磷细菌,数量均值分别为19.26×104 cfu·L-1、18.82×104cfu·L-1和19.56×102cfu·g-1;无机磷细菌只分布在长江口内和河口南槽至舟山海域,数量均值分别为18.50×104cfu·L-1、31.00×104cfu·L-1和7.17×102cfu·g-1;反硝化细菌分布广,但数量较低,均值分别为3.94×104个·L-1、23.08×104个·L-1和6.22×102个·g-1.相关性分析结果说明:盐度、硝酸盐、磷酸盐、硅酸盐和pH是影响水体和表层沉积物异养细菌、磷细菌和反硝化细菌分布的主要因子;底层水和表层沉积物异养细菌、磷细菌与水温呈显著正相关;底层水异养细菌和有机磷细菌与溶解氧(DO)呈显著正相关;表层沉积物无机磷细菌与DO呈显著正相关,氨化细菌与DO呈显著负相关.聚类分析结果说明:低氧对表层沉积物的细菌群落结构产生影响.     

我国东南沿海亚历山大藻休眠孢囊的分布和萌发研究

对4个海域的塔玛亚历山大藻(Alerandrium tamarense)和链状亚历山大藻(A．catenella)休眠孢囊的分布及萌发进行了研究．结果表明,厦门港仅在X1和X2站位有分布,且密度很小(0．4个·g-1);广西只在G2站位有发现,密度较少(2．5个·g-1泥样)．闽江口有3个站位有分布,M4站位的4～6cm层密度最大,达到6个·g-1泥样;长江口的孢囊分布广、密度大,DG-26站位的8～10cm层孢囊密度达到了23．2个·g-1泥样．孢囊的分布与沉积物底质类型、沉积速率、海流都有一定的关系．光照对孢囊萌发没有影响,温度升高导致萌发率和存活率均增大,而萌发时间缩短;在低氧条件下(0．01mgO2L-1),孢囊萌发率为0．亚历山大藻孢囊在合适的环境条件下终年都会萌发     

Estimation of methanotroph abundance in a freshwater lake sediment

The numbers of methane-oxidizing bacteria (methanotrophs) in the sediments of Lake Washington were estimated using three culture-independent methods. Quantitative slot-blot hybridizations were performed with type I and type II methanotroph-specific probes. These data were compared to data from quantitative hybridizations using a pmoA-specific probe and a eubacterial probe. From the combined hybridization data, the methanotroph population in Lake Washington was estimated to be 3.6 x 10(8)-7.4 x 10(8) cells/g dry weight. Methanotroph community structure and number were also investigated using polar lipid fatty acid (PLFA) analysis. Analysis of biomarker PLFAs characteristic of both type I (16:1 omega 8) and type II (18:1 omega 8) methanotrophs was used to estimate the abundance of these bacteria in Lake Washington sediments. From the PLFA data, the methanotroph population in Lake Washington was estimated to be 7.1 x 10(8)-9.4 x 10(9) cells/g dry weight. As a third method of quantitation, we calculated the methanotroph population using the total methane oxidation rate for whole cells in Lake Washington sediment to be 1.3 x 10(8)-1.2 x 10(9) cells/g dry weight. The three independent estimates of the number of methanotrophs in Lake Washington sediment agree within a two- to fourfold range. These data suggest that the three techniques used in this study detect the functionally significant population of methanotrophs in Lake Washington. Furthermore, these techniques will be useful for obtaining estimates of methanotroph abundance in additional environments.     

Application of antisera raised against sulfate-reducing bacteria for indirect immunofluorescent detection of immunoreactive bacteria in sediment from the German Baltic Sea.

Polyclonal rabbit antisera raised against sulfate-reducing bacteria (SRB) could detect several distinct populations of bacteria in sediment from the German Baltic Sea. The depth distribution of immunoreactive bacteria was determined by an indirect immunofluorescence filter method. Anti-Desulfovibrio desulfuricans DSM 1926 serum showed maximum bacterial numbers at a depth of 18 cm, with a concentration of 60 x 10(6) cells cm-3. With anti-Desulfovibrio baculatus DSM 2555 serum, counts were highest at the same depth, approaching 0.7 x 10(6) cells cm-3. Other significantly smaller populations were observed. Anti-SRBStrain 1 (lactate,vibrio) maxima were at 0 to 4 cm and at 17 to 18 cm. Anti-SRBStrain 2 (lactate,vibrio) serum showed several local maxima. Anti-SRBStrain 3 (lactate,oval) serum detected one single peak at a depth of 10 to 12 cm. Also determined were rates of sulfate reduction, total bacterial counts by acridine orange staining, and the viable counts by dilution series on anaerobic lactate medium. The total bacterial counts were highest (180 x 10(6) cells cm-3) at 3 to 4 cm and dropped to 24 x 10(6) cells cm-3 at 10 to 11 cm but showed additional local maxima reaching 140 x 10(6) cells cm-3 at a depth of 17 to 18 cm. Viable counts probable number) were above 10(5) CFU cm-3 at 0 to 3.6 cm but remained below 10(3) CFU at 7.2 to 18 cm. The sulfate reduction rate was maximal (107 nmol cm-3 day-1) at a depth of 1 to 2 cm, dropped to 10 nmol cm-3 day-1 at 12 to 13 cm, and reached 38 nmol cm-3 day-1 at 17 to 18 cm.     

泥螺养殖滩涂异养菌群和弧菌的检测

1　引　　言泥螺 (Ｂｕｌｌａｃｔａｅｘａｒａｔａ)隶属腹足纲软体动物 ,肉质鲜嫩、营养丰富 ,是浙江沿海重要的滩涂养殖品种 .至 2 0 0 0年浙江省养殖面积已达 1.13× 10 4ｈｍ2 ,由于实行生态养殖 ,本轻利厚 ,广受养农的青睐 .随着泥螺养殖生产的发展 ,养殖业的自身污染和陆源排污水的大量入海 ,养殖生态环境越趋恶化 ,使生物病原大量滋生 ,自 1995年以来常诱发养殖泥螺的暴发性死亡 .有关海洋滩涂环境细菌的研究至今未见报道 .为探明泥螺养殖周期内暴发性死亡与滩涂环境的关系 ,对养殖滩涂的细菌菌群组成及其生态特性进行了检测分析 .2…     

Large fraction of dead and inactive bacteria in coastal marine sediments: comparison of protocols for determination and ecological significance

It is now universally recognized that only a portion of aquatic bacteria is actively growing, but quantitative information on the fraction of living versus dormant or dead bacteria in marine sediments is completely lacking. We compared different protocols for the determination of the dead, dormant, and active bacterial fractions in two different marine sediments and at different depths into the sediment core. Bacterial counts ranged between (1.5 +/- 0.2) x 10(8) cells g(-1) and (53.1 +/- 16.0) x 10(8) cells g(-1) in sandy and muddy sediments, respectively. Bacteria displaying intact membrane (live bacterial cells) accounted for 26 to 30% of total bacterial counts, while dead cells represented the most abundant fraction (70 to 74%). Among living bacterial cells, nucleoid-containing cells represented only 4% of total bacterial counts, indicating that only a very limited fraction of bacterial assemblage was actively growing. Nucleoid-containing cells increased with increasing sediment organic content. The number of bacteria responsive to antibiotic treatment (direct viable count; range, 0.3 to 4.8% of the total bacterial number) was significantly lower than nucleoid-containing cell counts. An experiment of nutrient enrichment to stimulate a response of the dormant bacterial fraction determined a significant increase of nucleoid-containing cells. After nutrient enrichment, a large fraction of dormant bacteria (6 to 11% of the total bacterial number) was "reactivated." Bacterial turnover rates estimated ranged from 0.01 to 0.1 day(-1) but were 50 to 80 times higher when only the fraction of active bacteria was considered (on average 3.2 day(-1)). Our results suggest that the fraction of active bacteria in marine sediments is controlled by nutrient supply and availability and that their turnover rates are at least 1 order of magnitude higher than previously reported.     

Microbial production and consumption of dimethyl sulfide (DMS) in a sea grass (Zostera noltii)-dominated marine intertidal sediment ecosystem (Bassin d'Arcachon, France)

The relation between net dimethyl sulfide (DMS) production and changes in near surface (0-5 mm) oxygen concentrations in a sea grass (Zostera noltii Hornem)-covered intertidal sediment ecosystem was examined during a diel cycle. Sediment covered with Zostera was found to be more oxygenated than uncovered sediment during the period of photosynthesis. This phenomenon was probably caused by radial oxygen loss of the Zostera root-rhizome system. The population sizes of the three functional groups of microbes mainly responsible for the concentration of DMS, the dimethylsulfoniopropionate (DMSP)-demethylating, DMSP-cleaving and DMS-oxidizing bacteria, were quantified by most probable number (MPN) methodologies. Sediments with Zostera supported substantially higher populations of both aerobic (149x10(6) cm(-3) DMSP-utilizing and 0.4x10(6) cm(-3) DMS-oxidizing) and anaerobic (43x10(6) cm(-3) DMSP-utilizing and 0.4x10(6) cm(-3) DMS-oxidizing) microorganisms than sediments without Zostera (DMSP-utilizing aerobes and anaerobes both 2x10(6) cm(-3) and DMS-oxidizing aerobes and anaerobes both 0.2x10(6) cm(-3)). Experiments conducted with sediment cores and sediment slurries suggested that the net production of DMS in these sediments was significantly lower during oxic periods than during anoxic periods. Intact sediment cores with and without Zostera produced DMS when incubated under anoxic/dark conditions (97.0 and 53.6 nmol DMS m(-2) h(-1), respectively), while oxic/light-incubated cores did not produce detectable amounts of DMS. In addition, kinetic parameter values (V(max) and K(m)) for DMSP degradation in cell suspensions of isolated DMSP-demethylating and DMSP-cleaving bacteria were measured and compared to documented values for other strains. Both V(max) and K(m) values for DMSP-demethylating organisms were found to be relatively low (14.4-20.1 nmol DMSP mg protein(-1) min(-1) and 4.1-15.5 μM, respectively) while these parameter values varied widely in the group of the DMSP-cleaving organisms (6.7-1000 nmol DMSP mg protein(-1) min(-1) and 2-2000 μM, respectively). It was hypothesized that a diel rhythm in DMS emission occurred, with a relatively low net production during the day and a high net production during the night. Environmental changes which result in increased anoxic conditions in coastal sediments, such as an increase in eutrophication, may therefore result in increased atmospheric DMS emission rates.