Construction and characterization of a fosmid library for pathogenic bacterium Vibrio anguillarum

Vibrio anguillarum is a common bacterial pathogen in fish.However,little is known about its pathogenic mechanism,in part,because the entire genome has not been completely sequenced.We constructed a fosmid library for V.anguillarum containing 960 clones with an average insert size of 37.7 kb and 8.6-fold genome coverage.We characterized the library by end-sequencing 50 randomly selected clones.This generated 93 sequences with a total length of 57 485 bp covering 1.4% of the whole genome.Of these sequences,58(62.4%) were homologous to known genes,30(32.3%) were genes with hypothetical functions,and the remaining 5(5.3%) were unknown genes.We demonstrated the utility of this library by PCR screening of 10 genes.This resulted in an average of 6.2 fosmid clones per screening.This fosmid library offers a new tool for gene screening and cloning of V.anguillarum,and for comparative genomic studies among Vibrio species.

Construction and Characterization of Grass Carp (Ctenopharyngodon idellus) Fosmid Library

Grass carp （Ctenopharyngodon idellus） genomic fosmid library cotaining 129 014 clones was constructed and characterized from one diploid grass carp. The average insert size of the fosmid library was determined to be 35 kb by pulsed field gel electrophoresis, which is 4.1-fold coverage of the grass carp genome. To demonstrate the probability of picking the functional genes from the library, eleven functional genes were screened by three-dimensional PCR technique. The number of positive clones of these genes was from 1 to 6. So, this library may screen any useful genes from grass carp. This grass carp genome fosmid library will be integrated in the presently ongoing efforts to determine the sequence of the grass carp genome.

Construction,Characterization,and Chromosomal Mapping of a Fosmid Library of the White-Cheeked Gibbon (Nomascus leucogenys)

Gibbons have experienced extensive karyotype rearrangements during evolution and represent an ideal model for studying the underlying molecular mechanism of evolutionary chromosomal rearrangements. It is anticipated that the cloning and sequence characterization of evolutionary chromosomal breakpoints will provide vital insights into the molecular force that has driven such a radical karyotype reshuffle in gibbons. We constructed and characterized a high-quality fosmid li- brary of the white-cheeked gibbon （Nomascus leucogenys） containing 192,000 non- redundant clones with an average insert size of 38 kb and 2.5-fold genome coverage. By end sequencing of 100 randomly selected fosmid clones, we generated 196 se- quence tags for the library. These end-sequenced fosmid clones were then mapped onto the chromosomes of the white-cheeked gibbon by fluorescence in situ hy- bridization~ and no spurious chimeric clone was detected. BLAST search against the human genome showed a good correlation between the number of hit clones and the number of chromosomes, an indication of unbiased chromosomal distribu- tion of the fosmid library. The chromosomal distribution of the mapped clones is also consistent with the BLAST search result against human and white-cheeked gibbon genomes. The fosmid library and the mapped clones will serve as a valu- able resource for further studying gibbons＇ chromosomal rearrangements and the underlying molecular mechanism as well as for comparative genomic study in the lesser apes.

Construction of random sheared fosmid library from Chinese cabbage and its use for Brassica rapa genome sequencing project

As a part of the Multinational Genome Sequencing Project of Brassica rapa, linkage group R9 and R3 were sequenced using a bacterial artificial chromosome （BAC） by BAC strategy. The current physical contigs are expected to cover approximately 90% euchromatins of both chromosomes. As the project progresses, BAC selection for sequence extension becomes more limited because BAC libraries are restriction enzyme-specific. To support the project, a random sheared fosmid library was constructed. The library consists of 97536 clones with average insert size of approximately 40 kb corresponding to seven genome equivalents, assuming a Chinese cabbage genome size of 550 Mb. The library was screened with primers designed at the end of sequences of nine points of scaffold gaps where BAC clones cannot be selected to extend the physical contigs. The selected positive clones were end-sequenced to check the overlap between the fosmid clones and the adjacent BAC clones. Nine fosmid clones were selected and fully sequenced. The sequences revealed two completed gap filling and seven sequence extensions, which can be used for further selection of BAC clones confirming that the fosmid library will facilitate the sequence completion of B. rapa.

Screening and characterization of a novel ruminal cellulase gene(Umcel-1) from a metagenomic library of gayal(Bos frontalis)

Gayal is a rare semi-wild bovine species found in the Indo-China. They can graze grasses, including bamboo leaves, as well as reeds and other plant species, and grow to higher mature live weights than Yunnan Yellow cattle maintained in similar harsh environments. The aim of this study was to identify specific cellulase in the gayal rumen. A metagenomic fosmid library was constructed using genomic DNA isolated from the ruminal contents of four adult gayals. This library contained 38400 clones with an average insert size of 35.5 kb. The Umcel-1 gene was isolated from this library. Investigation of the cellulase activity of 24 random clones led to the identification of the Umcel-1 gene, which exhibited the most potent cellulase activity. Sequencing the Umcel-1 gene revealed that it contained an open reading frame of 942 base pairs that encoded a product of 313 amino acids. The putative gene Umcel-1 product belonged to the glycosyl hydrolase family 5 and showed the highest homology to the cellulase （GenBank accession no. YP_004310852.1 ） from Clostridium lentocellum DSM 5427, with 44% identity and 62% similarity. The Umcel-1 gene was heterologously expressed in Escherichia coil BL21, and recombinant Umcel-1 was purified. The activity of purified recombinant Umcel-1 was assessed, and the results revealed that it hydrolyzed carboxymethyl cellulose with optimal activity at pH 5.5 and 45~C. To our knowledge, this study provides the first evidence for a cellulase produced by bacteria in gayal rumen.