TOXICITY OF SOME MARINE SNAILS RESPONSIBLE FOR RECENT FOOD POISONINGS IN VIETNAM

During the years of 2006 - 2007, about five food poisoning cases with fatalities caused by marine snails reported in coastal areas of Vietnam. From stock over of poisoning materials from three out of five cases, causative species were identified as Nassarius papillosus, Nassasius (Alectrion) glans glans, N. (Zeuxis) comptus and Natica (Natica) fasciata. These species also caused poisonings in several countries such as Japan, the Philippines, Brunei and Taiwan. High level of tetrodotoxin was found in the specimens of N. papillosus as the causative component for food poisoning with three patients including two deaths on October 17, 2006 in Quang Ngai province.  In contrast, no tetrodotoxin was detected in three other snail species which were eaten at the poisonings on December 17, 2007 in Ninh Thuan province and December 27, 2007 in Binh Thuan province. Although the origin of tetrodotoxin in marine snails has not been clarified yet, it is urgently necessary to warn potential risks from marine snails to public as some of them may become suddenly toxic with unknown mechanism. Tóm tắt: Có ít nhất 5 vụ ngộ độc thực phẩm do ăn ốc biển được ghi nhận tại các vùng ven biển Việt Nam trong các năm 2006-2007. Mẫu vật ốc biển còn sót lại của 3 trong số 5 vụ ngộ độc này được xác định thuộc các loài Nassarius papillosus, Nassasius (Alectrion) glans glans, N. (Zeuxis) comptus và Natica (Natica) fasciata. Đây cũng là những loài gây ra những vụ ngộ độc tương tự ở một số Quốc gia khác như Nhật Bản, Phi-lip-pin, Brunây và Đài Loan. Bằng phương pháp sắc ký lỏng hiệu năng cao (HPLC), đã xác định được hàm lượng khá cao độc tố tetrodotoxin (TTX)  trong mẫu vật của loài N. papillosus gây ra vụ ngộ độc cho 3 nạn nhân (2 tử vong) ngày 17 - 10 - 2006 tại tỉnh Quảng Ngãi. Ngược lại, không tìm thấy sự có mặt của độc tố TTX trong 3 loài ốc biển nghi ngờ gây ra 2 vụ ngộ độc khác vào 17 - 12 - 2007 tại Ninh Thuận và 27 - 12 - 2007 tại Bình Thuận. Mặc dù nguồn gốc của độc tố TTX trong ốc biển vẫn còn chưa được biết đến, nhưng một số loài ốc biển có thể trở nên độc một cách bất thường vào một thời điểm nhất định nào đó, do vậy cần thiết phải có cảnh báo về nguy cơ ngộ độc từ những loài sinh vật này

VI SINH VẬT BIỂN: NGUỒN CÁC CHẤT TỰ NHIÊN CÓ HOẠT TÍNH SINH HỌC ỨNG DỤNG TRONG NGHIÊN CỨU DƯỢC

Marine microbiology is currently the topic that scientists worldwide are interested in with the aim of searching for bioactive substances. In addition to the inherent microorganisms in marine sediments, other marine lives - associated microorganisms have recently been more invested and important achievements of pharmaceutical research applications have been gained in the last few decades. In this article, we review the milestones in the process of looking for “drugs from the sea” and focus on remarkable results in marine microbes associated with invertebrate and their potential application in drug investigation from the latest published papers in prestigious international journals.Vi sinh vật biển hiện đang là đối tượng mà các nhà khoa học trên toàn thế giới quan tâm nghiên cứu cho mục đích tìm kiếm các chất có hoạt tính sinh học. Ngoài những vi sinh vật cố hữu trong trầm tích biển, vi sinh vật sống cùng sinh vật biển khác gần đây được nghiên cứu nhiều hơn và thu được nhiều thành quả đáng kể, ứng dụng tìm kiếm thuốc chữa bệnh trong vài thập kỷ qua. Trong bài này, chúng tôi điểm lại những mốc quan trọng trong quá trình tìm kiếm “thuốc từ biển”, đồng thời tổng quan một số kết quả nghiên cứu nổi bật gần nhất được công bố trên các tạp chí uy tín trên thế giới về sự đa dạng của vi sinh vật biển sống cùng động vật không xương sống và tiềm năng ứng dụng nghiên cứu dược của chúng

Dinophysis spp. recorded in the coastal waters of northern Vietnam during 2002-2003

A monitoring on toxins responsible for Diarrhetic Shellfish Poisoning (DSP) was carried out at several culture areas of hard clam (Meretrix meretrix) in the northern coast of Vietnam during May 2002 and December 2003. Quantitative observation of Dinophysis spp. was made one to four times every month and DSP toxins in the hard clam grown in the area was analyzed monthly using the HPLC method. Six species of Dinophysis were recorded, including D. caudata, D. fortii, D. miles, D. rotundata, D. mitra and D. hastata. Among them, D. caudata was the most common species. Others were not common and their densities were ignorable. D. caudata appeared almost all around the year at all sampling sites with density ranged from 0 to more than 3000 cells/l. However, it was more abundant during the warm period, i.e. from late February to late November. For the rest of a year, cells were rarely found. D. caudata was recorded in a wide range of temperature (15-34.3℃), but its significant density (over 100 cells/l) was only observed when water temperature exceeded 20℃. D. caudata appeared and could reach high density at all salinity in the range of 8-34 PSU. The highest recorded density was 3128 cells/l at 22℃ and 8.2 PSU in Thanh Hoa area in February 2003. ""Blooms"" of D. caudata, together with other dominant dinoflagellates, usually coincided with the vanishing period of diatoms. Okadaic acid (OA) was detected in edible part of clams but at low concentration in all samples. Maximal level was 80ng OA/100g, encountered in Thanh Hoa transect during August 2002 and April 2003. DTX 1-4 were not detected in all samples. No significant correlation between OA concentration in clam and the density of D. caudata in the water sample was observed, although toxins sometimes peaked the same time with D. caudata density. Low concentration of toxins implicates low risk of DSP and explains the absence of poisoning cases in the area so far. However, other shellfishes in the area should also be subjected to toxin monitoring

Bacteria associated with soft coral from Mot island - Nha Trang bay and their antimicrobial activities

Microbial communities associated with invertebrates had been considered as a new source of bioactive compounds. The soft coral associated bacteria in Mot island, Nha Trang bay were isolated, extracted and assessed for antagonistic activity against human and coral pathogens, the strongly active strains were identified by 16S rRNA analysis. The soft coral associated bacterium SCN10 had abcd antibacterial pattern which was named for inhibition towards Bacillus subtilis (pattern a), Escherichia coli (pattern b), Salmonella typhimurium (pattern c) and Serratia marcescens (pattern d). It was the nearest strain to the well-known antibiotic producer Bacillus amyloliquefaciens with 99% sequence similarity. Whereas strain SCL19 had abde pattern which means inhibition of the growth of B. subtilis, E. coli, S. marcescens and Vibrio parahaemolyticus (pattern e). This strain SCL19 affiliated with Bacillus sp. strain A-3-23B with 99.8% identity. In addition to antimicrobial activity to the aforementioned tested bacteria, the isolate SCX15 also inhibited Vibrio alginolyticus (pattern f) and Candida albicans (pattern g), so this isolate possessed abcdefg antimicrobial pattern. The coral associated isolate SCX15 was identified as Bacillus velezensis with 99% sequence similarity. Among the 78 screened strains, 25 isolates possessed antibacterial activity against at least one of seven tested microorganisms and exhibited 12 different types of antimicrobial activities, suggesting that they can produce many different natural substances with antibacterial activity

Domoic acid in a bivalve Spondylus cruentus in Nha Trang Bay, Khanh Hoa Province, Vietnam

Recently we have found that domoic acid (DA), a toxin responsible for amnesic shellfish poisoning, is always detected in bivalve species belonging to a genus Spondylus randomly collected from various parts of the tropical areas including Vietnam. In Vietnam, 10 species of Spondylus are known to grow. Among these species, S. cruentus is a commercially valuable species. Domoic acid in S. cruentus collected in Nha Trang Bay is analyzed by ELISA and LC/MS/MS. Remarkable individual difference was observed in DA level among 28 specimens of S. cruentus collected from the same area at the same time. The DA level in S. cruentus apparently showed a seasonal variation. However, the variation of DA content seems to be due to a large individual difference among the specimens. When the specimens were reared in plankton-free conditions, DA level in S. cruentus did not decreaseds for 45 days, showing that S. cruentus maintains DA for a long period

Analysis of rDNA reveals a high genetic diversity of Halophila major in the Wallacea region

The genus Halophila shows the highest species diversity within the seagrass genera. Southeast Asian countries where several boundary lines exist were considered as the origin of seagrasses. We hypothesize that the boundary lines, such as Wallace’s and Lydekker’s Lines, may act as marine geographic barriers to the population structure of Halophila major. Seagrass samples were collected at three islands in Vietnamese waters and analyzed by the molecular maker ITS. These sequences were compared with published ITS sequences from seagrasses collected in the whole region of interest. In this study, we reveal the haplotype and nucleotide diversity, linking population genetics, phylogeography, phylogenetics and estimation of relative divergence times of H. major and other members of the Halophila genus. The morphological characters show variation. The results of the ITS marker analysis reveal smaller groups of H. major from Myanmar, Shoalwater Bay (Australia) and Okinawa (Japan) with high supporting values. The remaining groups including Sri Lanka, Viet Nam, the Philippines, Thailand, Malaysia, Indonesia, Two Peoples Bay (Australia) and Tokushima (Japan) showed low supporting values. The Wallacea region shows the highest haplotype and also nucleotide diversity. Non-significant differences were found among regions, but significant differences were presented among populations. The relative divergence times between some members of section Halophila were estimated 2.15–6.64 Mya

Field Equations in General Relativity with Internal Symmetry

The covariant wedge products of tetrads in General Relativity are introduced and related field equations are derived. The electromagnetic dual field is treated in detail and it is shown that this field is closely related with one component field, which is eigenfunction of d'Alembertian operator. The formalism is developed to incorporate internal symmetry