Allan Cembella | Alfred Wegener Institute for Polar and Marine Research (original) (raw)
Papers by Allan Cembella
The Harmful Algal Bloom species Alexandrium fundeyense is responsible for outbreaks of paralytic ... more The Harmful Algal Bloom species Alexandrium fundeyense is responsible for outbreaks of paralytic shellfish poisoning in the marine realm of temperate waters. Unknown lytic compounds produced by A. fundeyense are highly discussed to facilitate the formation of these toxic blooms by reducing losses due to competition and grazing. However, avoiding being consumed has to be efficient enough to succeed among other prey organisms. We therefore identified possible feedback mechanisms that A. fundeyense might gain from the lytic compound production on the molecular level. Based on a comprehensive cDNA-library we compared the transcriptional response towards a protistan grazer (Polykrikos kofoidii) of an A. fundeyense strain capable of lytic compound production vs a strain that lacks this ability. We will further highlight genes involved in secondary metabolite synthesis that are differentially expressed between these two strains. Our results strongly suggest that the action of lytic compounds produced by A. fundeyense is associated with an induction of a wide range of cellular functions. Thus, lytic compound production seems to be a trait with more far reaching consequences than only a release from top-down processes. In summary, our results will give novel insights and issues for consideration regarding the autecology of this prominent HAB-species.
The field of marine microbial ecology of eukaryotes started to flourish due to large scale projec... more The field of marine microbial ecology of eukaryotes started to flourish due to large scale projects and new methodological innovations in molecular ecology and genomics. In line, functional analysis of marine microeukaryotic communities that combine biodiversity patterns and metatranscriptome profiles to define taxon-specific activities are only recently emerging. We will present a comprehensive dataset that links abiotic measurements to microeukaryotic community composition and its respective metatranscriptome profiles. The analysis of our metatranscriptome profiles was enabled due to the Marine Microbial Eukaryotic Transcriptome Sequencing Project (MMETSP). Specifically we will show how diversity and taxon-specific transcription patterns change within and between different ecosystems. Our data are derived from I) Disko Bay, an Arctic ecosystem located at the west coast of Greenland (69°N), II) North Atlantic waters influenced by the Gulf Stream around the islands of the Lofoten at the west coast of Norway (68/69°N) and III) a mixed water body ecosystem (North Sea / Baltic Sea) in the Kattegat around the island of Orust (58°N), located at the west coast of Sweden. Each ecosystem is represented by 5 different sampling stations. Abiotic environmental measurements contain temperature, salinity, chlorophyll, macronutrients (N and P) and silica. Molecular diversity was assessed via amplicon sequencing of the 28s hypervariable D1/D2 region with the 454 technology. Metatranscriptomic data was obtained with RNAseq using the Illumina 100 paired-end technologies.
Ecogenomics is an advanced approach to biodiversity research that can serve to define evolutionar... more Ecogenomics is an advanced approach to biodiversity research that can serve to define evolutionary relationships and species interactions within complex ecosystems. Current hypotheses propose that impacts of environmental changes on the biodiversity, composition and bioactivity of species are particularly pronounced in Arctic regions. Our study focused on the comparison of molecular biodiversity of four planktonic size-fractions (micro-, nano-, pico- and bacterioplankton) in coastal waters of Greenland and Iceland, and the consequences for ecosystem functioning. Molecular diversity was assessed via sequencing the 28S hypervariable D1/D2 region, or the 16 rDNA for 454 amplicon sequencing. Metatranscriptomic data were assessed using Illumina 100 paired-end technology. We showed that biodiversity distribution within the two areas differed markedly within and among size-fractions. In general, we observed a higher diversity, as well as higher similarities between Greenland and Iceland station transects, within smaller size-fractions. Diversity differences between the regions were highly correlated with temperature and salinity, but also with silicate and phosphate concentrations impact. This pattern was also reflected in activity profiles deduced from the metatranscriptomic analyses.
Harmful Algae, Oct 1, 2022
Marine Biology, Aug 13, 1999
Harmful Algae, Oct 1, 2022
Alexandrium minutum is a widely distributed HAB dinoflagellate that typically produces PSP neurot... more Alexandrium minutum is a widely distributed HAB dinoflagellate that typically produces PSP neurotoxins (gonyautoxins 1,2,3,4), as well as poorly characterized allelochemicals. Within the EU-Project ESTTAL (Expressed Sequence Tags of Toxic Algae), we aim to identify candidate genes and processes putatively involved in toxicity and allelochemical interactions, and in growth regulation and stress responses. To obtain RNA samples linked with physiological status, batch cultures of A. minutum were grown under different environmental conditions, yielding differences in growth, PSP toxin production, and allelochemical potency. As a basis for gene expression analysis, we generated a normalized cDNA library, from which about 10,000 expressed sequence tags (ESTs) were generated. Annotation of these data yielded first insights into the genome of A. minutum. Based on the EST library, we designed an oligonucleotide microarray, which will be used to screen for differences in gene expression among the differently treated A. minutum cultures. Here we present the results of the EST library analysis, the design of the microarray, and physiological data of cultures grown for gene expression analysis.
Cylindrospermopsis raciborskii is a filamentous, potentially toxic bloom-forming cyanobacterium i... more Cylindrospermopsis raciborskii is a filamentous, potentially toxic bloom-forming cyanobacterium in tropical and temperate freshwaters. We compared the cylindrospermopsin (CYN) producing C. raciborskii strain CS-505 (Australia) against a PSP toxin producing strain D9 (Brazil), originally identified as conspecific. Cylindrospermopsis raciborskii forms a monophyletic group comprising identities >99% for the 16S rRNA gene, whereas strains D9 and CS-505 are 99.7% similar. We sequenced the complete genome of these strains, the first for any PSP- or CYN-toxin producing cyanobacterium. The genome sizes are the smallest known for filamentous cyanobacteria (3.3 and 3.9 Mbp for D9 and CS-505, respectively), but exhibit an apparently large size difference. Genome comparison yielded 471 and 801 strain-specific genes for D9 and CS-505, respectively, and revealed remarkable differences between strains. These differences are mainly related to signatures for high genomic plasticity in CS-505, gene loss in D9 (such as the lack of nitrogen fixation genes), and genes for secondary metabolite production, specifically in the STX and CYN clusters. Functional analysis via gene expression studies using microarrays and qPCR have supported the function of the identified toxin-related gene clusters as well as indicating fundamental differences in phenotypic expression between the strains.
In marine ecosystems the interactions among protists and prokaryotes (eubacteria and cyanobacteri... more In marine ecosystems the interactions among protists and prokaryotes (eubacteria and cyanobacteria) and effects on zooplankton play a dominant role in food web ecology and trophodynamics. Among protists and cyanobacteria, species considered to be harmful algae can cause harm by forming aggregations of cells known as harmful algal blooms (HABs). Certain harmful algae can cause negative ecological effects even at relatively low cell concentrations by production of potent phycotoxins, thereby killing or incapacitating micro-grazers and diverse organisms such as fish, sea-birds and marine mammals by vectorial transfer through marine food webs. Although the ecological role of phycotoxins is poorly understood, the obvious ability of toxic protists to survive, thrive and occasionally to dominate the plankton via the formation of blooms, supports the hypothesis that these bioactive secondary metabolites have a distinct function in the ecological success and evolution of the species.A key component for defining the factors responsible for bloom development is the biochemical and molecular regulation of the toxic and other allelochemical interactions among grazers, prey, and competitors. Knowledge of the genes and enzymes involved in phycotoxin production and their metabolic regulation within the cell, and molecular regulation of other secondary metabolites that may function as allelochemicals, is very limited. Functional genomic and proteomic studies on regulation of phycotoxins/allelochemicals are crucial for our understanding of the molecular ecology of toxigenic microalgae. Studies on genetic regulation and intrinsic control mechanisms of growth and cell proliferation are also required. During the last few years, rapid advances in molecular technologies are allowing us to begin to address this lack of knowledge. Whole genome sequencing and limited genomic approaches, such as expressed sequence tags (ESTs), complemented with the development of DNA-microarrays, are powerful tools to address questions in functional genomics. Application of a spectrum of molecular methods has begun to yield valuable insights into the genetic regulation of processes such as growth and toxin synthesis in marine protists.
Harmful Algae, Nov 1, 2020
Coupling Physiological Responses of the Toxic Haptophyte Prymnesium parvum to Patterns in Gene Ex... more Coupling Physiological Responses of the Toxic Haptophyte Prymnesium parvum to Patterns in Gene ExpressionMichael F. Freitag1, Uwe John1 & AD Cembella11Alfred Wegener Institute for Polar and Marine research, 27576 Bremerhaven, Germany 2Sara Beszteri, Alfred Wegener Institute, Bremerhaven GermanyA normalized cDNA library2 from the toxic haptophyte Prymnesium parvum was used to design an oligonucleotide-based microarray platform. Allelopathic interactions were investigated between P. parvum strain RL10 and the heterotrophic dinoflagellate Oxyhrris marina. Cultures of Prymnesium were incubated together with both whole cells and cell-free filtrate from Oxyhrris cultures. During incubation with Prymnesium, the presence of Oxyhrris cells, compared to cell-free culture medium, showed no differential effect on the gene expression profile of the haptophyte. A bioassay measuring the toxicity of Prymnesium against the sensitive cryptophyte Rhodomonas baltica was additionally performed. In this case, Rhodomonas viabilities following incubation with Prymnesium and Prymnesium previously incubated with O. marina medium were virtually identical. This suggests no correlation between the presence of O. marina medium, and induced toxicity in P. parvum. Similar experiments, involving the dinoflagellate Heterocapsa rotunda and an unclassified toxic crooccal cyanobacteria strain: NIVA CYA 331, are currently underway. All tentative unique genes (TUGs) identified from the microarray hybridization will be further classified through the use of a Prymnesium fosmid library prepared from axenic cultures.
The Harmful Algal Bloom species Alexandrium fundeyense is responsible for outbreaks of paralytic ... more The Harmful Algal Bloom species Alexandrium fundeyense is responsible for outbreaks of paralytic shellfish poisoning in the marine realm of temperate waters. Unknown lytic compounds produced by A. fundeyense are highly discussed to facilitate the formation of these toxic blooms by reducing losses due to competition and grazing. However, avoiding being consumed has to be efficient enough to succeed among other prey organisms. We therefore identified possible feedback mechanisms that A. fundeyense might gain from the lytic compound production on the molecular level. Based on a comprehensive cDNA-library we compared the transcriptional response towards a protistan grazer (Polykrikos kofoidii) of an A. fundeyense strain capable of lytic compound production vs a strain that lacks this ability. We will further highlight genes involved in secondary metabolite synthesis that are differentially expressed between these two strains. Our results strongly suggest that the action of lytic compounds produced by A. fundeyense is associated with an induction of a wide range of cellular functions. Thus, lytic compound production seems to be a trait with more far reaching consequences than only a release from top-down processes. In summary, our results will give novel insights and issues for consideration regarding the autecology of this prominent HAB-species.
The field of marine microbial ecology of eukaryotes started to flourish due to large scale projec... more The field of marine microbial ecology of eukaryotes started to flourish due to large scale projects and new methodological innovations in molecular ecology and genomics. In line, functional analysis of marine microeukaryotic communities that combine biodiversity patterns and metatranscriptome profiles to define taxon-specific activities are only recently emerging. We will present a comprehensive dataset that links abiotic measurements to microeukaryotic community composition and its respective metatranscriptome profiles. The analysis of our metatranscriptome profiles was enabled due to the Marine Microbial Eukaryotic Transcriptome Sequencing Project (MMETSP). Specifically we will show how diversity and taxon-specific transcription patterns change within and between different ecosystems. Our data are derived from I) Disko Bay, an Arctic ecosystem located at the west coast of Greenland (69°N), II) North Atlantic waters influenced by the Gulf Stream around the islands of the Lofoten at the west coast of Norway (68/69°N) and III) a mixed water body ecosystem (North Sea / Baltic Sea) in the Kattegat around the island of Orust (58°N), located at the west coast of Sweden. Each ecosystem is represented by 5 different sampling stations. Abiotic environmental measurements contain temperature, salinity, chlorophyll, macronutrients (N and P) and silica. Molecular diversity was assessed via amplicon sequencing of the 28s hypervariable D1/D2 region with the 454 technology. Metatranscriptomic data was obtained with RNAseq using the Illumina 100 paired-end technologies.
Ecogenomics is an advanced approach to biodiversity research that can serve to define evolutionar... more Ecogenomics is an advanced approach to biodiversity research that can serve to define evolutionary relationships and species interactions within complex ecosystems. Current hypotheses propose that impacts of environmental changes on the biodiversity, composition and bioactivity of species are particularly pronounced in Arctic regions. Our study focused on the comparison of molecular biodiversity of four planktonic size-fractions (micro-, nano-, pico- and bacterioplankton) in coastal waters of Greenland and Iceland, and the consequences for ecosystem functioning. Molecular diversity was assessed via sequencing the 28S hypervariable D1/D2 region, or the 16 rDNA for 454 amplicon sequencing. Metatranscriptomic data were assessed using Illumina 100 paired-end technology. We showed that biodiversity distribution within the two areas differed markedly within and among size-fractions. In general, we observed a higher diversity, as well as higher similarities between Greenland and Iceland station transects, within smaller size-fractions. Diversity differences between the regions were highly correlated with temperature and salinity, but also with silicate and phosphate concentrations impact. This pattern was also reflected in activity profiles deduced from the metatranscriptomic analyses.
Harmful Algae, Oct 1, 2022
Marine Biology, Aug 13, 1999
Harmful Algae, Oct 1, 2022
Alexandrium minutum is a widely distributed HAB dinoflagellate that typically produces PSP neurot... more Alexandrium minutum is a widely distributed HAB dinoflagellate that typically produces PSP neurotoxins (gonyautoxins 1,2,3,4), as well as poorly characterized allelochemicals. Within the EU-Project ESTTAL (Expressed Sequence Tags of Toxic Algae), we aim to identify candidate genes and processes putatively involved in toxicity and allelochemical interactions, and in growth regulation and stress responses. To obtain RNA samples linked with physiological status, batch cultures of A. minutum were grown under different environmental conditions, yielding differences in growth, PSP toxin production, and allelochemical potency. As a basis for gene expression analysis, we generated a normalized cDNA library, from which about 10,000 expressed sequence tags (ESTs) were generated. Annotation of these data yielded first insights into the genome of A. minutum. Based on the EST library, we designed an oligonucleotide microarray, which will be used to screen for differences in gene expression among the differently treated A. minutum cultures. Here we present the results of the EST library analysis, the design of the microarray, and physiological data of cultures grown for gene expression analysis.
Cylindrospermopsis raciborskii is a filamentous, potentially toxic bloom-forming cyanobacterium i... more Cylindrospermopsis raciborskii is a filamentous, potentially toxic bloom-forming cyanobacterium in tropical and temperate freshwaters. We compared the cylindrospermopsin (CYN) producing C. raciborskii strain CS-505 (Australia) against a PSP toxin producing strain D9 (Brazil), originally identified as conspecific. Cylindrospermopsis raciborskii forms a monophyletic group comprising identities >99% for the 16S rRNA gene, whereas strains D9 and CS-505 are 99.7% similar. We sequenced the complete genome of these strains, the first for any PSP- or CYN-toxin producing cyanobacterium. The genome sizes are the smallest known for filamentous cyanobacteria (3.3 and 3.9 Mbp for D9 and CS-505, respectively), but exhibit an apparently large size difference. Genome comparison yielded 471 and 801 strain-specific genes for D9 and CS-505, respectively, and revealed remarkable differences between strains. These differences are mainly related to signatures for high genomic plasticity in CS-505, gene loss in D9 (such as the lack of nitrogen fixation genes), and genes for secondary metabolite production, specifically in the STX and CYN clusters. Functional analysis via gene expression studies using microarrays and qPCR have supported the function of the identified toxin-related gene clusters as well as indicating fundamental differences in phenotypic expression between the strains.
In marine ecosystems the interactions among protists and prokaryotes (eubacteria and cyanobacteri... more In marine ecosystems the interactions among protists and prokaryotes (eubacteria and cyanobacteria) and effects on zooplankton play a dominant role in food web ecology and trophodynamics. Among protists and cyanobacteria, species considered to be harmful algae can cause harm by forming aggregations of cells known as harmful algal blooms (HABs). Certain harmful algae can cause negative ecological effects even at relatively low cell concentrations by production of potent phycotoxins, thereby killing or incapacitating micro-grazers and diverse organisms such as fish, sea-birds and marine mammals by vectorial transfer through marine food webs. Although the ecological role of phycotoxins is poorly understood, the obvious ability of toxic protists to survive, thrive and occasionally to dominate the plankton via the formation of blooms, supports the hypothesis that these bioactive secondary metabolites have a distinct function in the ecological success and evolution of the species.A key component for defining the factors responsible for bloom development is the biochemical and molecular regulation of the toxic and other allelochemical interactions among grazers, prey, and competitors. Knowledge of the genes and enzymes involved in phycotoxin production and their metabolic regulation within the cell, and molecular regulation of other secondary metabolites that may function as allelochemicals, is very limited. Functional genomic and proteomic studies on regulation of phycotoxins/allelochemicals are crucial for our understanding of the molecular ecology of toxigenic microalgae. Studies on genetic regulation and intrinsic control mechanisms of growth and cell proliferation are also required. During the last few years, rapid advances in molecular technologies are allowing us to begin to address this lack of knowledge. Whole genome sequencing and limited genomic approaches, such as expressed sequence tags (ESTs), complemented with the development of DNA-microarrays, are powerful tools to address questions in functional genomics. Application of a spectrum of molecular methods has begun to yield valuable insights into the genetic regulation of processes such as growth and toxin synthesis in marine protists.
Harmful Algae, Nov 1, 2020
Coupling Physiological Responses of the Toxic Haptophyte Prymnesium parvum to Patterns in Gene Ex... more Coupling Physiological Responses of the Toxic Haptophyte Prymnesium parvum to Patterns in Gene ExpressionMichael F. Freitag1, Uwe John1 & AD Cembella11Alfred Wegener Institute for Polar and Marine research, 27576 Bremerhaven, Germany 2Sara Beszteri, Alfred Wegener Institute, Bremerhaven GermanyA normalized cDNA library2 from the toxic haptophyte Prymnesium parvum was used to design an oligonucleotide-based microarray platform. Allelopathic interactions were investigated between P. parvum strain RL10 and the heterotrophic dinoflagellate Oxyhrris marina. Cultures of Prymnesium were incubated together with both whole cells and cell-free filtrate from Oxyhrris cultures. During incubation with Prymnesium, the presence of Oxyhrris cells, compared to cell-free culture medium, showed no differential effect on the gene expression profile of the haptophyte. A bioassay measuring the toxicity of Prymnesium against the sensitive cryptophyte Rhodomonas baltica was additionally performed. In this case, Rhodomonas viabilities following incubation with Prymnesium and Prymnesium previously incubated with O. marina medium were virtually identical. This suggests no correlation between the presence of O. marina medium, and induced toxicity in P. parvum. Similar experiments, involving the dinoflagellate Heterocapsa rotunda and an unclassified toxic crooccal cyanobacteria strain: NIVA CYA 331, are currently underway. All tentative unique genes (TUGs) identified from the microarray hybridization will be further classified through the use of a Prymnesium fosmid library prepared from axenic cultures.