oalib
匹配条件: “” ,找到相关结果约100条。
列表显示的所有文章,均可免费获取
第1页/共100条
每页显示
Biosynthesis and Molecular Genetics of Polyketides in Marine Dinoflagellates  [PDF]
Ralf Kellmann,Anke Stüken,Russell J. S. Orr,Helene M. Svendsen,Kjetill S. Jakobsen
Marine Drugs , 2010, DOI: 10.3390/md8041011
Abstract: Marine dinoflagellates are the single most important group of algae that produce toxins, which have a global impact on human activities. The toxins are chemically diverse, and include macrolides, cyclic polyethers, spirolides and purine alkaloids. Whereas there is a multitude of studies describing the pharmacology of these toxins, there is limited or no knowledge regarding the biochemistry and molecular genetics involved in their biosynthesis. Recently, however, exciting advances have been made. Expressed sequence tag sequencing studies have revealed important insights into the transcriptomes of dinoflagellates, whereas other studies have implicated polyketide synthase genes in the biosynthesis of cyclic polyether toxins, and the molecular genetic basis for the biosynthesis of paralytic shellfish toxins has been elucidated in cyanobacteria. This review summarises the recent progress that has been made regarding the unusual genomes of dinoflagellates, the biosynthesis and molecular genetics of dinoflagellate toxins. In addition, the evolution of these metabolic pathways will be discussed, and an outlook for future research and possible applications is provided.
Discovery of Nuclear-Encoded Genes for the Neurotoxin Saxitoxin in Dinoflagellates  [PDF]
Anke Stüken,Russell J. S. Orr,Ralf Kellmann,Shauna A. Murray,Brett A. Neilan,Kjetill S. Jakobsen
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0020096
Abstract: Saxitoxin is a potent neurotoxin that occurs in aquatic environments worldwide. Ingestion of vector species can lead to paralytic shellfish poisoning, a severe human illness that may lead to paralysis and death. In freshwaters, the toxin is produced by prokaryotic cyanobacteria; in marine waters, it is associated with eukaryotic dinoflagellates. However, several studies suggest that saxitoxin is not produced by dinoflagellates themselves, but by co-cultured bacteria. Here, we show that genes required for saxitoxin synthesis are encoded in the nuclear genomes of dinoflagellates. We sequenced >1.2×106 mRNA transcripts from the two saxitoxin-producing dinoflagellate strains Alexandrium fundyense CCMP1719 and A. minutum CCMP113 using high-throughput sequencing technology. In addition, we used in silico transcriptome analyses, RACE, qPCR and conventional PCR coupled with Sanger sequencing. These approaches successfully identified genes required for saxitoxin-synthesis in the two transcriptomes. We focused on sxtA, the unique starting gene of saxitoxin synthesis, and show that the dinoflagellate transcripts of sxtA have the same domain structure as the cyanobacterial sxtA genes. But, in contrast to the bacterial homologs, the dinoflagellate transcripts are monocistronic, have a higher GC content, occur in multiple copies, contain typical dinoflagellate spliced-leader sequences and eukaryotic polyA-tails. Further, we investigated 28 saxitoxin-producing and non-producing dinoflagellate strains from six different genera for the presence of genomic sxtA homologs. Our results show very good agreement between the presence of sxtA and saxitoxin-synthesis, except in three strains of A. tamarense, for which we amplified sxtA, but did not detect the toxin. Our work opens for possibilities to develop molecular tools to detect saxitoxin-producing dinoflagellates in the environment.
Characterisation of the paralytic shellfish toxin biosynthesis gene clusters in Anabaena circinalis AWQC131C and Aphanizomenon sp. NH-5
Troco K Mihali, Ralf Kellmann, Brett A Neilan
BMC Biochemistry , 2009, DOI: 10.1186/1471-2091-10-8
Abstract: We describe the identification, annotation and bioinformatic characterisation of the putative paralytic shellfish toxin biosynthesis clusters in an Australian isolate of Anabaena circinalis and an American isolate of Aphanizomenon sp., both members of the Nostocales. These putative PST gene clusters span approximately 28 kb and contain genes coding for the biosynthesis and export of the toxin. A putative insertion/excision site in the Australian Anabaena circinalis AWQC131C was identified, and the organization and evolution of the gene clusters are discussed. A biosynthetic pathway leading to the formation of saxitoxin and its analogues in these organisms is proposed.The PST biosynthesis gene cluster presents a mosaic structure, whereby genes have apparently transposed in segments of varying size, resulting in different gene arrangements in all three sxt clusters sequenced so far. The gene cluster organizational structure and sequence similarity seems to reflect the phylogeny of the producer organisms, indicating that the gene clusters have an ancient origin, or that their lateral transfer was also an ancient event. The knowledge we gain from the characterisation of the PST biosynthesis gene clusters, including the identity and sequence of the genes involved in the biosynthesis, may also afford the identification of these gene clusters in dinoflagellates, the cause of human mortalities and significant financial loss to the tourism and shellfish industries.Paralytic shellfish poisoning (PSP) is a syndrome acquired through the consumption of contaminated shellfish or drinking water. Its symptoms include numbness and ascending paralysis followed by respiratory arrest [1]. Toxicity is mediated by a group of toxins collectively referred to as paralytic shellfish toxins (PSTs) or saxitoxins (STX).The global occurrence of PSTs coupled with their chemical stability and high toxicity, presents a formidable problem for marine and freshwater regulating bodies, while detrimenta
Origin of Saxitoxin Biosynthetic Genes in Cyanobacteria  [PDF]
Ahmed Moustafa, Jeannette E. Loram, Jeremiah D. Hackett, Donald M. Anderson, F. Gerald Plumley, Debashish Bhattacharya
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0005758
Abstract: Background Paralytic shellfish poisoning (PSP) is a potentially fatal syndrome associated with the consumption of shellfish that have accumulated saxitoxin (STX). STX is produced by microscopic marine dinoflagellate algae. Little is known about the origin and spread of saxitoxin genes in these under-studied eukaryotes. Fortuitously, some freshwater cyanobacteria also produce STX, providing an ideal model for studying its biosynthesis. Here we focus on saxitoxin-producing cyanobacteria and their non-toxic sisters to elucidate the origin of genes involved in the putative STX biosynthetic pathway. Methodology/Principal Findings We generated a draft genome assembly of the saxitoxin-producing (STX+) cyanobacterium Anabaena circinalis ACBU02 and searched for 26 candidate saxitoxin-genes (named sxtA to sxtZ) that were recently identified in the toxic strain Cylindrospermopsis raciborskii T3. We also generated a draft assembly of the non-toxic (STX?) sister Anabaena circinalis ACFR02 to aid the identification of saxitoxin-specific genes. Comparative phylogenomic analyses revealed that nine putative STX genes were horizontally transferred from non-cyanobacterial sources, whereas one key gene (sxtA) originated in STX+ cyanobacteria via two independent horizontal transfers followed by fusion. In total, of the 26 candidate saxitoxin-genes, 13 are of cyanobacterial provenance and are monophyletic among the STX+ taxa, four are shared amongst STX+ and STX-cyanobacteria, and the remaining nine genes are specific to STX+ cyanobacteria. Conclusions/Significance Our results provide evidence that the assembly of STX genes in ACBU02 involved multiple HGT events from different sources followed presumably by coordination of the expression of foreign and native genes in the common ancestor of STX+ cyanobacteria. The ability to produce saxitoxin was subsequently lost multiple independent times resulting in a nested relationship of STX+ and STX? strains among Anabaena circinalis strains.
Insights on the evolution of trehalose biosynthesis
Nelson Avonce, Alfredo Mendoza-Vargas, Enrique Morett, Gabriel Iturriaga
BMC Evolutionary Biology , 2006, DOI: 10.1186/1471-2148-6-109
Abstract: In this study we show that trehalose biosynthesis ability is present in eubacteria, archaea, plants, fungi and animals. In bacteria there are five different biosynthetic routes, whereas in fungi, plants and animals there is only one. We present phylogenetic analyses of the trehalose-6-phosphate synthase (TPS) and trehalose-phosphatase (TPP) domains and show that there is a close evolutionary relationship between these domains in proteins from diverse organisms. In bacteria TPS and TPP genes are clustered, whereas in eukaryotes these domains are fused in a single protein.We have demonstrated that trehalose biosynthesis pathways are widely distributed in nature. Interestingly, several eubacterial species have multiple pathways, while eukaryotes have only the TPS/TPP pathway. Vertebrates lack trehalose biosynthetic capacity but can catabolise it. TPS and TPP domains have evolved mainly in parallel and it is likely that they have experienced several instances of gene duplication and lateral gene transfer.One of the fundamental challenges for an organism is to survive changes in the physical environment-mainly extreme temperatures, salinity, or dehydration. This problem was to be solved very early in evolution since the first cells inhabited the primitive seas [1,2]. Organisms evolved two different strategies to contend with abiotic stress. In certain species that live in extreme environments, for instance strict thermophiles and halophiles, the metabolic capabilities were modified, such that the optimal enzymatic activity or membrane stability are at high temperature or salinity, respectively [3]. Other organisms when exposed to extreme conditions have a drastically different adaptation to contend with stress. They evolved biosynthetic pathways for osmotically active compounds, cryoprotectants or thermoprotectants, thus enabling survival until conditions are favourable again. Among these compounds are polyols such as mannitol, sorbitol, some amino acids (proline and glu
Neurotoxic Alkaloids: Saxitoxin and Its Analogs  [PDF]
Maria Wiese,Paul M. D’Agostino,Troco K. Mihali,Michelle C. Moffitt,Brett A. Neilan
Marine Drugs , 2010, DOI: 10.3390/md8072185
Abstract: Saxitoxin (STX) and its 57 analogs are a broad group of natural neurotoxic alkaloids, commonly known as the paralytic shellfish toxins (PSTs). PSTs are the causative agents of paralytic shellfish poisoning (PSP) and are mostly associated with marine dinoflagellates (eukaryotes) and freshwater cyanobacteria (prokaryotes), which form extensive blooms around the world. PST producing dinoflagellates belong to the genera Alexandrium, Gymnodinium and Pyrodinium whilst production has been identified in several cyanobacterial genera including Anabaena, Cylindrospermopsis, Aphanizomenon Planktothrix and Lyngbya. STX and its analogs can be structurally classified into several classes such as non-sulfated, mono-sulfated, di-sulfated, decarbamoylated and the recently discovered hydrophobic analogs—each with varying levels of toxicity. Biotransformation of the PSTs into other PST analogs has been identified within marine invertebrates, humans and bacteria. An improved understanding of PST transformation into less toxic analogs and degradation, both chemically or enzymatically, will be important for the development of methods for the detoxification of contaminated water supplies and of shellfish destined for consumption. Some PSTs also have demonstrated pharmaceutical potential as a long-term anesthetic in the treatment of anal fissures and for chronic tension-type headache. The recent elucidation of the saxitoxin biosynthetic gene cluster in cyanobacteria and the identification of new PST analogs will present opportunities to further explore the pharmaceutical potential of these intriguing alkaloids.
Multi-gene analysis of Symbiodinium dinoflagellates: a perspective on rarity, symbiosis, and evolution  [PDF]
Xavier Pochon,Hollie M. Putnam,Ruth D. Gates
PeerJ , 2015, DOI: 10.7717/peerj.394
Abstract: Symbiodinium, a large group of dinoflagellates, live in symbiosis with marine protists, invertebrate metazoans, and free-living in the environment. Symbiodinium are functionally variable and play critical energetic roles in symbiosis. Our knowledge of Symbiodinium has been historically constrained by the limited number of molecular markers available to study evolution in the genus. Here we compare six functional genes, representing three cellular compartments, in the nine known Symbiodinium lineages. Despite striking similarities among the single gene phylogenies from distinct organelles, none were evolutionarily identical. A fully concatenated reconstruction, however, yielded a well-resolved topology identical to the current benchmark nr28S gene. Evolutionary rates differed among cellular compartments and clades, a pattern largely driven by higher rates of evolution in the chloroplast genes of Symbiodinium clades D2 and I. The rapid rates of evolution observed amongst these relatively uncommon Symbiodinium lineages in the functionally critical chloroplast may translate into potential innovation for the symbiosis. The multi-gene analysis highlights the potential power of assessing genome-wide evolutionary patterns using recent advances in sequencing technology and emphasizes the importance of integrating ecological data with more comprehensive sampling of free-living and symbiotic Symbiodinium in assessing the evolutionary adaptation of this enigmatic dinoflagellate.
Evolution of Lysine Biosynthesis in the Phylum Deinococcus-Thermus  [PDF]
Hiromi Nishida,Makoto Nishiyama
International Journal of Evolutionary Biology , 2012, DOI: 10.1155/2012/745931
Abstract: Thermus thermophilus biosynthesizes lysine through the α-aminoadipate (AAA) pathway: this observation was the first discovery of lysine biosynthesis through the AAA pathway in archaea and bacteria. Genes homologous to the T. thermophilus lysine biosynthetic genes are widely distributed in bacteria of the Deinococcus-Thermus phylum. Our phylogenetic analyses strongly suggest that a common ancestor of the Deinococcus-Thermus phylum had the ancestral genes for bacterial lysine biosynthesis through the AAA pathway. In addition, our findings suggest that the ancestor lacked genes for lysine biosynthesis through the diaminopimelate (DAP) pathway. Interestingly, Deinococcus proteolyticus does not have the genes for lysine biosynthesis through the AAA pathway but does have the genes for lysine biosynthesis through the DAP pathway. Phylogenetic analyses of D. proteolyticus lysine biosynthetic genes showed that the key gene cluster for the DAP pathway was transferred horizontally from a phylogenetically distant organism. 1. Introduction The Deinococcus-Thermus phylum constitutes one of the major bacterial evolutionary lineages [1, 2]. At present, the genome sequence data of 6 genera (13 organisms) belonging to this phylum are available in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database [3]. Two pathways for lysine biosynthesis have been described, namely, the α-aminoadipate (AAA) pathway and the diaminopimelate (DAP) pathway [5]. The AAA pathway has two different types [6]. In T. thermophilus, a gene cluster was found for lysine biosynthesis not through the DAP pathway but through the AAA pathway [6–8]. Although Deinococcus radiodurans has genes homologous to the T. thermophilus lysine biosynthetic genes, these genes are scattered on the genome [9]. In addition, the D. radiodurans aspartate kinase that catalyzes the phosphorylation of L-aspartate (the first reaction in the DAP pathway) is structurally and phylogenetically very different from that of T. thermophilus [10]. Recent studies have shown that the genome signatures of these 2 bacteria are different [4], supporting the theory that Deinococcus species acquired genes from various other bacteria to survive different kinds of environmental stresses, whereas Thermus species have acquired genes from thermophilic bacteria to adapt to high-temperature environments [11]. The distribution of lysine biosynthetic genes in the Deinococcus-Thermus phylum has not been clearly described. In this study, we compared the distribution of the genes for lysine biosynthesis between 13 organisms (D. deserti, D.
An Overview on the Marine Neurotoxin, Saxitoxin: Genetics, Molecular Targets, Methods of Detection and Ecological Functions  [PDF]
Kathleen D. Cusick,Gary S. Sayler
Marine Drugs , 2013, DOI: 10.3390/md11040991
Abstract: Marine neurotoxins are natural products produced by phytoplankton and select species of invertebrates and fish. These compounds interact with voltage-gated sodium, potassium and calcium channels and modulate the flux of these ions into various cell types. This review provides a summary of marine neurotoxins, including their structures, molecular targets and pharmacologies. Saxitoxin and its derivatives, collectively referred to as paralytic shellfish toxins (PSTs), are unique among neurotoxins in that they are found in both marine and freshwater environments by organisms inhabiting two kingdoms of life. Prokaryotic cyanobacteria are responsible for PST production in freshwater systems, while eukaryotic dinoflagellates are the main producers in marine waters. Bioaccumulation by filter-feeding bivalves and fish and subsequent transfer through the food web results in the potentially fatal human illnesses, paralytic shellfish poisoning and saxitoxin pufferfish poisoning. These illnesses are a result of saxitoxin’s ability to bind to the voltage-gated sodium channel, blocking the passage of nerve impulses and leading to death via respiratory paralysis. Recent advances in saxitoxin research are discussed, including the molecular biology of toxin synthesis, new protein targets, association with metal-binding motifs and methods of detection. The eco-evolutionary role(s) PSTs may serve for phytoplankton species that produce them are also discussed.
Surface Plasmon Spectroscopic Detection of Saxitoxin  [PDF]
Hongxia Chen,Youn Sook Kim,Sam-Rok Keum,Sung-Hoon Kim,Heung-Jin Choi,Jaebeom Lee,Won Gun An,Kwangnak Koh
Sensors , 2007, DOI: 10.3390/s7071216
Abstract: For the surface-optoelectronic study of Saxitoxin sensing, we fabricated self-assembled calix[4]arene derivative monolayers as the recognition-functional interfaces ona gold surface. An interaction study between Saxitoxin and calix[4]arene derivativemonolayers were performed using surface plasmon resonance (SPR) spectroscopy. Amongthree calix[4]arene derivatives, calix[4]arene crown ether SAM showed the highestsensitivity to Saxitoxin. The detection limit of this system is three orders of magnitudelower than that of the mouse bioassay which is the current benchmark for Saxitoxindetection.
第1页/共100条
每页显示


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.