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分布式GIS的海量数据和有限带宽的网络资源之间矛盾日益突出,远程矢量数据的查询和海量数据传输成为解决问题的关键。在分析海量数据查询特点的基础上,结合空间数据库中数据层的查询优化方法和代价函数,提出了一个在客户端定义并使用代价函数优化动态规划的矢量数据查询方法,同时在客户端实现数据拓扑差查询。实践证明,该方法能够有效提高查询速度和保持全局网络负载的良好性能。 相似文献
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Genetic engineering in filamentous N2-fixing cyanobacteria usually involves Anabaena sp. PCC 7120 and several other non-aggregating species. Mass culture and harvest of such species are more energy consuming
relative to aggregating species. To establish a gene transfer system for aggregating species, we tested many species of Anabaena and Nostoc, and identified Nostoc muscorum FACHB244 as a species that can be genetically manipulated using the conjugative gene transfer system. To promote biodegradation
of organophosphorus pollutants in aquatic environments, we introduced a plasmid containing the organophosphorus-degradation
gene (opd) into Anabaena sp. PCC 7120 and Nostoc muscorum FACHB244 by conjugation. The opd gene was driven by a strong promoter, P
psbA
. From both species, we obtained transgenic strains having organophosphorus-degradation activities. At 25°C, the whole-cell
activities of the transgenic Anabaena and Nostoc strains were 0.163±0.001 and 0.289±0.042 unit/μg Chl a, respectively. However, most colonies resulting from the gene transfer showed no activity. PCR and DNA sequencing revealed
deletions or rearrangements in the plasmid in some of the colonies. Expression of the green fluorescent protein gene from
the same promoter in Anabaena sp. PCC 7120 showed similar results. These results suggest that there is the potential to promote the degradation of organophosphorus
pollutants with transgenic cyanobacteria and that selection of high-expression transgenic colonies is important for genetic
engineering of Anabaena and Nostoc species. For the first time, we established a gene transfer and expression system in an aggregating filamentous N2-fixing cyanobacterium. The genetic manipulation system of Nostoc muscorum FACHB244 could be utilized in the elimination of pollutants and large-scale production of valuable proteins or metabolites. 相似文献
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The morphological and molecular detection for the presence of toxic Cylindrospermopsis(Nostocales,Cyanobacteria) in Beijing city,China 总被引：1，自引：0，他引：1
Cylindrospermopsis raciborskii and its highly similar relatives R aphidiopsis species have been recognized as globally invasive and expansive filamentous cyanobacteria causing water blooms. Reports on C. raciborskii/Raphidiopsis species and their harmful metabolites such as hepatotoxic cylindrospermopsins(CYNs) in Chinese waters have been increasing, but mostly restricted to the southern regions of China. To further explore the existence and distribution of C. raciborskii in China, six water samples from Beijing city were morphologically and molecularly examined. Five samples of the six were shown to have C ylindrospermopsis filaments with straight and spiral morphotypes. PCR detection targeting on Cylindrospermopsis/Raphidiopsis specific 16 S r RNA gene region also showed the positive amplification, and such amplifications were confirmed by sequencing and phylogenetic analysis. As well, three of the five Cylindrospermopsis containing samples were shown to have c yr J — a gene of CYN synthesis gene cluster. The results represented the presence of toxic C ylindrospermopsis at the most northern line in China so far, indicating rapid expansion of this harmful invasive cyanobacterium. It is strongly suggested that the monitoring on C. raciborskii/R aphidiopsis species and their production of cylindrospermopsin should be emphasized in Beijing and even more northern parts of China. 相似文献
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