Yang Guanpin

Cylindrotheca closterium Is a Species Complex as Was Evidenced by the Variations of rbcL Gene and SSU rDNA

The genus Cylindrotheca consists of a small group of marine diatoms with a few species described. Eleven isolates of diatoms identified as Cylindrotheca closterium morphologically were obtained from Jiaozhou Bay with their nuclear-encoded small-subunit ribosomal RNA (SSU rDNA) and chloroplast-encoded rbcL gene sequences determined in this study. Interestingly, very high sequence divergences of SSU rDNA and rbcL gene were found among these isolates, and numerous nucleotide variation of rbcL gene caused relatively few variation of deduced amino acid sequence. Phylogenetic analyses based on SSU rDNA and rbcL gene, respectively, grouped the isolates into 6 clades. Phylogenetic tree of SSU rDNA placed all the Cylindrotheca isolates together, separating them into two lineages clearly. Lineage I was composed of the eleven C. closterium isolates obtained in this study together with another C. closterium isolate, but some clades were not well supported. Lineage II contained two C. closterium isolates and one C. fusiformis isolate. Phylogenetic analysis of rbcL gene also separated the Cylindrotheca isolates into two well-defined lineages. The eleven C. closterium isolates formed a lineage and all clades were supported strongly. Statistical comparisons of SSU rDNA indicated that the average distance within lineage I was significantly higher than that of other microalgae species (P < 0.01). These results suggested the existence of cryptic species within C. closterium.

Design of Vibrio 16S rRNA Gene Specific Primers and Their Application in the Analysis of Seawater Vibrio Community

The pathogenic species of genusVibrio cause vibriosis, one of the most prevalent diseases of maricultured animals and seafood consumers. Monitoring their kinetics in the chain of seafood production, processing and consumption is of great importance for food and mariculture safety. In order to enrichVibrio-representing 16S ribosomal RNA gene (rDNA) fragments and identify these bacteria further real-timely and synchronously among bacterial flora in the chain, a pair of primers that selectively amplifyVibrio 16S rDNA fragments were designed with their specificities and coverage testified in the analysis of seawaterVibrio community. The specificities and coverage of two primers, VF169 and VR744, were determined theoretically among bacterial 16S rDNAs available in GenBank by using BLAST program and practically by amplifying,Vibrio 16S rDNA fragments from seawater DNA. More than 88.3% of sequences in GenBank, which showed identical matches with VR744, belong toVibrio genus. A total of 33 clones were randomly selected and sequenced. All of the sequences showed their highest similarities to and clustered around those of diverse knownVibrio species. The primers designed are capable of retrieving a wide range ofVibrio 16S rDNA fragments specifically among bacterial flora in seawater, the most important natural environment of seafood cultivation.

Expression detection of DMRTs and two sox9 genes in Takifugu rubripes (Tetraodontidae, Vertebrata)

Sex determination and sex differentiation are important phenomena in fish, but the mechanisms of sex determination in Takifugu rubripes are poorly understood. In our study, the expression patterns of genes for DMRTs (DMRT1, DMRT2 and DMRT3), sox9a and sox9b in T. rubripes tissues were verified with the Reverse Transcription (RT)-PCR detection. It is showed that DMRT1 expressions in testis and ovaries were much lower, and no expressions were found in muscle, blood and tailfin. However, expressions for DMRT2 and DMRT3 were not found in the tissues stated above. Transcripts of sox9a were detected in muscle, fin, ovary and testis, but not in blood, whereas sox9b expression was only detected in ovary. The expression patterns of DMRTs, sox9a and sox9b in T. rubripes gonads suggest that these genes may not be sex-specific.

Nematode Diversity of Qingdao Coast Inferred from the 18S Ribosomal RNA Gene Sequence Analysis

The 18S ribosomal DNA gene (18S rDNA) sequences (approximately 1300 bp in length) were amplified from the DNA extracted from the free-living marine nematodes collected from the inter-tidal sediment of Qingdao coast in bulk with nematode specific primers. The PCR products were cloned, re-amplified, digested with Rsa I and Hin6 I restriction endonucleases and separated in agarose gel. Among 17 restriction fragment length types, types 1, 2 and 6 covered 61.2%, 14.4% and 9.3% of the clones analyzed, respectively, while the remaining 14 only covered 21 clones, which accounted for 15.1% of the total. Twenty-four representative clones were sequenced and phylogenetically analyzed by referring to those currently available in RDP and GenBank databases. Although it was hard to assign these sequences to known species or genera due to the lack of the 18S rDNA sequence data of known marine free-living nematodes, the obtained sequences were assigned to the nematodes of Adenophorea. Among them, twelve sequences were close to Pontonema vulgare and Adoncholaimus sp., four to Daptonema procerus and two (identical) to Enoplus brevis. Our results showed that free-living marine nematode diversities could be determined by PCR retrieving and analysis of the 18S rDNA sequences and an 18S rDNA sequence could be assigned to a species or a genus only if the 18S rDNA sequences of the free-living marine nematodes were accumulated to some extent.