淡水养殖水体细菌群落结构与硝化速率的关系

为研究3类淡水养殖水体(精养虾蟹池、湖泊养殖水体和精养鱼池)细菌群落结构与硝化速率的关系,通过16S rRNA基因高通量测序与流式细胞仪分析了 15个养殖水体的细菌种群结构和总菌数,并测定了硝化速率.结果表明:淡水养殖水体中的优势菌群门为变形菌门(Proteobacteria)、放线菌门(Acidobacteria)和...     

Biological productivity and carbon cycling in the Arctic Ocean

Primary production, bacterial production, particulate organic carbon fluxes and organic carbon burial rates were quantified during the summer period of 1999 in the Arctic Ocean via 14C uptake, 3H uptake, 234Th/238U disequilibrium and 210Pbex dating, respectively. The integrated primary production in the water column was as high as 197 mmolC/(m2@d) in the Chukchi shelf and was 3.8 mmolC/(m2@d) in the Canada Basin. These rates are higher than those reported previously. The ratios of bacterial production to primary production in the study region were higher than 0.5, indicating that microbial activity is not depressed but important in cold Arctic waters. 234Th/238U disequilibria were evident at the station in the Canada Basin. The presence of significant 234Th deficiency suggested that scavenging and removal processes are also important to biogeochemical cycles of trace elements in the Arctic Ocean. Particulate organic carbon export flux was estimated to be 1.0 mmolC/(m2@d). Measurements of sediment excess 210Pb profile in the Chukchi shelf allowed us to estimate the amount of organic carbon buried in the bottom sediment, which ranged from 25 to 35 mmolC/(m2@d) and represented about 59%-82% of the mean primary production in the euphotic zone. Overall, our results indicated that the Arctic Ocean has active carbon cycling and is not a biological desert as previously believed. Therefore, the Arctic Ocean may play an important role in the global carbon cycle and climate change.     

木醋杆菌1.1812发酵产细菌纤维素的研究

通过单因素试验和正交试验对木醋杆菌1.1812液体发酵产细菌纤维素的培养基和培养条件进行优化,得到木醋杆菌1.1812发酵产细菌纤维素的适宜培养基和条件是:蔗糖5%,蛋白胨1.5%,柠檬酸0.2%,Na2HPO4.12H2O 0.2%,KH2PO40.2%,MgSO4.7H2O 0.03%,乙醇1%,pH值6.8,温度28℃,培养周期6 d。细菌纤维素产量干重为2 g/L。发酵完毕后过滤收集粗纤维,再用4%NaOH溶液冲洗,去离子水和0.5%乙酸反复冲洗,即获细菌纤维素。通过Sephadex G-150柱层析对细菌纤维素进行组成分析,发现木醋杆菌1.1812发酵所得的纤维素成分较为单一。     

谷胱甘肽S—转移酶5—5和细菌二氯甲烷脱卤素酶的性质比较

通过简便的两步阴离子交换色谱，从遗传工程菌株大肠杆菌ＪＭ１０５中纯化出哺乳动物的谷胱甘肽Ｓ－转移酶５－５（ＧＳＴ５－５），ＧＳＴ５－５以二卤甲烷为底物时的动力学常数，热稳定性和最适ｐＨ被测定，并与细菌二氯甲烷脱卤素酶的上述性质进行了比较。     

金矿中铜的细菌浸出——Ⅱ.氧化亚铁硫杆菌浸出含铜金精矿中的铜

从矿山酸性排水中分离出氧化亚铁的细菌菌株,经鉴定为氧化亚铁硫杆菌(Thiobacillus ferrooxidans);靠细菌的生物氧化作用浸出含铜金精矿中的铜。当浸出条件控制在pH2.0,温度30℃,矿浆浓度为15%,细菌接种量为10~6个细胞/ml,矿样含铜量为5.07%时,经摇瓶振荡浸出21天,铜的浸出率可达45%左右。最适浸出温度为35℃,超过38℃则生物学氧化作用停止。高温下浸出仅是化学作用为主。细菌浸渣经氰化实验,氰化钠消耗量较对照减少了81%。     

Aerobic anoxygenic phototrophic bacteria and their roles in marine ecosystems

Aerobic anoxygenic phototrophic bacteria(AAPB) are characterized by the following physiological and ecological features. A mother AAPB cell can unusually divide into 3 daughter cells and looks like a “Y” during the division. AAPB cells sometimes adhere together forming a free-floating population. Most of the known AAPB species are obligately aerobic. Bacteriochlorophyll a (BChl a) is the only photosynthetic pigment in AAPB, and the number of BChl a molecules in an AAPB cell is much less than that in an anaerobic phototrophic bacterial cell, while the accessorial pigments carotenoids in AAPB are abundant in concentration and diverse in species. In addition to the common magnesium containing BChl a, a zinc-containing BChla was also seen in AAPB. AAPB have light harvesting complex I but usually lack light harvesting complex II. Although AAPB featur in photosynthesis, their growth is not necessarily lightdependent. There is a mechanism controlling the photosynthesis approach. AAPB are widely distributed in marine environments especially in oligotrophic oceans accounting for a substantial portion of the total biomass and playing a unique role in the cycle of carbon and other biogenic elements. Besides the contribution to primary production, AAPB also have great potentials in bioremediation of polluted environments. Studies on AAPB would be of great value in understanding the evolution of photosynthesis and the structure and function of marine ecosystems.     

Obtaining transgenic rice resistant to rice fungal blast disease by controlled cell death strategy

The strategy of the two-component system,composed of Barnase and Barstar which encode RNase and a specific inhibitor to the RNase respectively, is adopted to obtain transgenic rice resistant to rice fungal blast disease. In this study, two chimeric promoters, induced by rice blast fungus pathogen (Magnaporthe grisea), are fused with Barnase respectively to construct two plant expression vectors, pWBNBS and pPBNBS together with the Barstar driven by CaMV 35S promoter. The resistance of the transgenic rice lines to rice blast fungus disease and rice blight disease are evaluated. The results show that (1) the expression of Barnase is induced in rice leaves when inoculated with the spores of Magnaporthe grisea; (2) the induced expression level of Barnase surpasses the level of Barstar, which elicits a similar hypersensitive response (HR) in the leaves, and the transgenic plant shows high resistance to the rice fungal blast disease; and (3) transgenic rice plants also show obvious resistance to rice bacterial blight disease. Taken together, these results suggest that the transgenic rice plants harboring this two-component system acquire relatively broad spectrum resistance against pathogens, especially high resistance to rice fungal pathogen.     

Lytic transglycosylases in macromolecular transport systems of Gram-negative bacteria

The cell wall of Gram-negative bacteria is essential for the integrity of the bacterial cell but also imposes a physical barrier to trans-envelope transport processes in which DNA and/or proteins are taken up or secreted by complex protein assemblies. The presence of genes encoding lytic transglycosylases in macromolecular transport systems (bacteriophage entry, type II secretion and type IV pilus synthesis, type III secretion, type IV secretion) suggests an important role for these specialised cell-wall-degrading enzymes. Such enzymes are capable of locally enlarging gaps in the peptidoglycan meshwork to allow the efficient assembly and anchoring of supramolecular transport complexes in the cell envelope. In this review, current knowledge on the role and distribution of these specialised murein-degrading enzymes in diverse macromolecular transport systems is summarised and discussed.Received 13 February 2003; received after revision 25 April 2003; accepted 12 May 2003     

Variations of sulfur and carbon isotopes in seawater during the Doushantuo stage in late Neoproterozoic

The Doushantuo Formation of the Sinian System in the Yangtze area is the first sedimentary stratigraphic unit after the Neoproterozoic Snowball Earth event[1], named the Nantuo Glaciation in south China. There are not only phosphorite and manganese mineralized beds[2], but also a series of biome which represents the biological radiation in Neoproterozoic[3] found in this formation. It is important to study the palaeoenvironment and the early biological evolution implied in the Doushantuo …