Project description:Proteins, lipids, and carbohydrates from the harmful algal bloom (HAB)-causing organism Pyrodinium bahamense were characterized to obtain insights into the biochemical processes in this environmentally relevant dinoflagellate. Shotgun proteomics using label-free quantitation followed by proteome mapping using the P. bahamense transcriptome and translated protein databases of Marinovum algicola, Alexandrium sp., Cylindrospermopsis raciborskii, and Symbiodinium kawagutii for annotation enabled the characterization of the proteins in P. bahamense. The highest number of annotated hits were obtained from M. algicola and highlighted the contribution of microorganisms associated with P. bahamense. Proteins involved in dimethylsulfoniopropionate (DMSP) degradation such as propionyl CoA synthethase and acryloyl-CoA reductase were identified, suggesting the DMSP cleavage pathway as the preferred route in this dinoflagellate. Most of the annotated proteins were involved in amino acid biosynthesis and carbohydrate degradation and metabolism, indicating the active roles of these molecules in the vegetative stage of P. bahamense. This characterization provides baseline information on the cellular machinery and the molecular basis of the ecophysiology of P. bahamense.
Project description:Saxitoxin (STX) is a secondary metabolite and potent neurotoxin produced by several genera of harmful algal bloom (HAB) marine dinoflagellates. The basis for variability in STX production within natural bloom populations is undefined as both toxic and non-toxic strains (of the same species) have been isolated from the same geographic locations. Pyrodinium bahamense is a STX-producing bioluminescent dinoflagellate that blooms along the east coast of Florida as well as the bioluminescent bays in Puerto Rico (PR), though no toxicity reports exist for PR populations. The core genes in the dinoflagellate STX biosynthetic pathway have been identified, and the sxtA4 gene is essential for toxin production. Using sxtA4 as a molecular proxy for the genetic capacity of STX production, we examined sxtA4+ and sxtA4- genotype frequency at the single cell level in P. bahamense populations from different locations in the Indian River Lagoon (IRL), FL, and Mosquito Bay (MB), a bioluminescent bay in PR. Multiplex PCR was performed on individual cells with Pyrodinium-specific primers targeting the 18S rRNA gene and sxtA4. The results reveal that within discrete natural populations of P. bahamense, both sxtA4+ and sxtA4- genotypes occur, and the sxtA4+ genotype dominates. In the IRL, the frequency of the sxtA4+ genotype ranged from ca. 80-100%. In MB, sxtA4+ genotype frequency ranged from ca 40-66%. To assess the extent of sxtA4 variation within individual cells, sxtA4 amplicons from single cells representative of the different sampling sites were cloned and sequenced. Overall, two variants were consistently obtained, one of which is likely a pseudogene based on alignment with cDNA sequences. These are the first data demonstrating the existence of both genotypes in natural P. bahamense sub-populations, as well as sxtA4 presence in P. bahamense from PR. These results provide insights on underlying genetic factors influencing the potential for toxin variability among natural sub-populations of HAB species and highlight the need to study the genetic diversity within HAB sub-populations at a fine level in order to identify the molecular mechanisms driving HAB evolution.
Project description:Epigenetic regulation of mutually exclusive transcription within the var gene family is important for infection and pathogenesis of the malaria parasite Plasmodium falciparum. var genes are kept transcriptionally silent via heterochromatic clusters located at the nuclear periphery; however, only a few proteins have been shown to play a direct role in var gene transcriptional regulation. Importantly, the chromatin components that contribute to var gene nuclear organization remain unknown. Here, we adapted a CRISPR-based immunoprecipitation-mass spectrometry approach for de novo identification of factors associated with specific transcriptional regulatory sequences of var genes. Tagged, catalytically inactive Cas9 (“dCas9”) was targeted to var gene promoters or introns, cross-linked, and immunoprecipitated with all DNA, proteins, and RNA associated with the targeted locus. Chromatin immunoprecipitation followed by sequencing demonstrated that genome-wide dCas9 binding was specific and robust. Proteomics analysis of dCas9-immunoprecipitates identified specific proteins for each target region, including known and novel factors such as DNA binding proteins, chromatin remodelers, and structural proteins. We also demonstrate the ability to immunoprecipitate RNA that is closely associated to the targeted locus. Our CRISPR/dCas9 study establishes a new tool for targeted purification of specific genomic loci and advances understanding of virulence gene regulation in the human malaria parasite.
Project description:The dataset comprises a whole-genome sequence of Ruegeria sp. PBVC088, a symbiotic (Gram-negative) bacterium associated with Pyrodinium bahamense var. compressum, which has been associated with harmful algal blooms in the coastal waters of west Sabah, Malaysia. Harmful algal blooms contribute to economic losses for the aquaculture industry, as well as human illnesses and fatalities due to paralytic shellfish poisoning. Bacteria-algae dynamics have posited that the interaction is potentially responsible for the toxin production during a toxic harmful algal bloom event. Despite the expanding body of literature on the capabilities of these bacteria to metabolize, produce, and modify toxins autonomously, it has yet to be confirmed that these toxin-producing bacteria are capable of autonomous toxin synthesis. Saxitoxin, a paralytic shellfish poisoning toxin, is produced by a unique biosynthetic pathway, where the genetic basis for the saxitoxin production was first reported in the saxitoxin-producing cyanobacteria strain Cylindrospermopsis raciborskii T3 (NCBI accession no. DQ787200). The genes responsible for saxitoxin biosynthesis in dinoflagellates, have yet to be fully elucidated. The identification of cyanobacteria saxitoxin biosynthesis genes (sxt) may eventually lead to the identification of homologous genes within the dinoflagellates. Previous studies on the diversity of the bacterial communities associated with the same toxic P. bahamense harmful alga has been carried out by using both the culture-dependent 16S ribosomal RNA gene sequence analysis and culture-independent 16S metagenomic sequence analysis. This study extends the knowledge pertaining to the genomic aspect of an associated bacterium isolated from P. bahamense alga by adopting a whole genome sequencing approach. Here, we report the genome sequencing, de novo assembly, and annotation data of a bacterium, Ruegeria sp. PBVC088, associated with harmful alga P. bahamense, which can be referenced by researchers to identify the genes and pathways related to toxin biosynthesis from a much larger data set. The genome of Ruegeria sp. PBVC088 was sequenced using the Illumina MiSeq platform with 250 bp paired-end reads. The number of reads generated from the MiSeq sequencer was 1,135,484, with an estimated coverage of 100X. The estimated genome size for the marine bacterium was computed to be 5.78 Mb. Annotation of the genome predicted 5,689 gene sequences, which were assigned putative functions based on homology to existing protein sequences in public databases. In addition, annotation of genes related to saxitoxin biosynthesis pathway was also performed. Raw fastq reads and the final version of the genome assembly have been deposited in the National Center for Biotechnology Information (NCBI) (BioProject: PRJNA324753, WGS: LZNT00000000, SRA: SRR3646181). The genome data provided here are expected to better understand the genetic processes involved in saxitoxin biosynthesis in marine bacteria associated with dinoflagellates.