Gap-free genome assembly of anadromous Coilia nasus.

The Chinese tapertail anchovy, Coilia nasus, is a socioeconomically important anadromous fish that migrates from near ocean waters to freshwater to spawn every spring. The analysis of genomic architecture and information of C. nasus were hindered by the previously released versions of reference genomes with gaps. Here, we report the assembly of a chromosome-level gap-free genome of C. nasus by incorporating high-coverage and accurate long-read sequence data with multiple assembly strategies. All 24 chromosomes were assembled without gaps, representing the highest completeness and assembly quality. We assembled the genome with a size of 851.67 Mb and used BUSCO to estimate the completeness of the assembly as 92.5%. Using a combination of de novo prediction, protein homology and RNA-seq annotation, 21,900 genes were functionally annotated, representing 99.68% of the total predicted protein-coding genes. The availability of gap-free reference genomes for C. nasus will provide the opportunity for understanding genome structure and function, and will also lay a solid foundation for further management and conservation of this important species.

A new species of mammalian trypanosome, Trypanosoma (Megatrypanum) bubalisi sp. nov., found in the freshwater leech Hirudinaria manillensis.

Leeches have long been considered potential vectors for the aquatic lineage of trypanosomes, while bloodsucking insects are generally considered as the vectors for the terrestrial lineage of trypanosomes. The freshwater leech, Hirudinaria manillensis, is a widely distributed species in southern China and could potentially act as the vector for trypanosomes. Prior to this study, no trypanosomes had been reported from this leech. However, in this study, leeches were collected from three different places in Guangdong province, China, and a large number of flagellates were isolated and successfully cultured in vitro. Based on morphology, these flagellates looked like a typical trypanosome species. Analysis was carried out on the molecular sequences of the 18S rRNA gene and the glycosomal glyceraldehyde-3-phosphate dehydrogenase (gGAPDH) gene. To our surprise, these flagellates were identified as likely to be a mammalian trypanosome belonging to the clade containing Trypanosoma (Megatrypanum) theileri but they are significantly different from the typical TthI and TthII stocks. Analyses of blood composition indicated that the source of the blood meal in these leeches was from the water buffalo (Bubalus bubalis). To further test if this flagellate from the freshwater leech was indeed a mammalian trypanosome, we transferred the trypanosomes cultured at 27-37 °C and they were able to successfully adapt to this mammalian body temperature, providing further supporting evidence. Due to the significant genetic differences from other related trypanosomes in the subgenus Megatrypanum, we propose that this flagellate, isolated from H. manillensis, is a new species and have named it Trypanosoma bubalisi. Our results indicate that freshwater leeches may be a potential vector of this new mammalian trypanosome.

Trehalose, an easy, safe and efficient cryoprotectant for the parasitic protozoan Trypanosoma brucei.

Trehalose, a non-permeating cryoprotective agent (CPA), has been documented as less toxic and highly efficient at cryopreserving different kinds of cells or organisms. In the present study, trehalose was evaluated for its application in cryopreservation of both Trypanosoma brucei procyclic and bloodstream form cells. The cryopreservation efficiency was determined by the motility of trypanosomes after thawing, as well as a subsequent recovery and infectivity assessment. The viability of trypanosomes from cultivation that were frozen in a serial concentrations of trehalose showed similar results to classical CPAs of glycerol and DMSO. Nevertheless, trypanosomes cryopreserved in 0.2M trehalose showed the best growth characteristic during subsequent cultivation. In addition, CPA cocktails with trehalose and permeating CPA glycerol or DMSO were developed and evaluated. Interestingly, trypanosomes in host (mouse) blood cryopreserved in 0.4M trehalose plus 5% glycerol showed higher infectivity than those preserved in trehalose/DMSO cocktails as well as individually. Further investigations showed that, in comparison with slow freezing at -80°C, flash freezing in liquid nitrogen provided better cryopreservation for bloodstream form cells than slow freezing. In conclusion, trehalose is an easy, safe and efficient CPA for cryopreservation of T. brucei and potentially for other protozoan species and cells.

Current status of Clonorchis sinensis and clonorchiasis in China.

The oriental liver fluke, Clonorchis sinensis, a pathogen causing clonorchiasis, is of major socio-economic importance in East Asia, including China, Korea and Vietnam. This parasite is now recognized as a biocarcinogen strongly linked to cholangiocarcinoma in humans. Here, we describe the status of clonorchiasis in China, where it has been estimated that more than 15 million patients are affected. This paper also summarizes the major advances in the field of clonorchiasis research during last decade, including diagnosis techniques, pathogenesis and genome/transcriptome/proteome studies in the last years. We strongly hope that our work can stimulate the governments of the countries or regions where clonorchiasis is endemic to pay more attention to this disease and establish related guidelines to prevent and control it.