Explore the vast range of titles available.

Brevetoxins (BTXs) are marine biotoxins responsible for neurotoxic shellfish poisoning (NSP) after ingestion of contaminated shellfish. NSP is characterized by neurological, gastrointestinal and/or cardiovascular symptoms. The main known producer of BTXs is the dinoflagellate Karenia brevis, but other microalgae are also suspected to synthesize BTX-like compounds. BTXs are currently not regulated in France and in Europe. In November 2018, they have been detected for the first time in France in mussels from a lagoon in the Corsica Island (Mediterranean Sea), as part of the network for monitoring the emergence of marine biotoxins in shellfish. To prevent health risks associated with the consumption of shellfish contaminated with BTXs in France, a working group was set up by the French Agency for Food, Environmental and Occupational Health & Safety (Anses). One of the aims of this working group was to propose a guidance level for the presence of BTXs in shellfish. Toxicological data were too limited to derive an acute oral reference dose (ARfD). Based on human case reports, we identified two lowest-observed-adverse-effect levels (LOAELs). A guidance level of 180 µg BTX-3 eq./kg shellfish meat is proposed, considering a protective default portion size of 400 g shellfish meat.

Efficient RNA extraction methods are needed to study transcript regulation. Such methods must lyse the cell without degrading the genetic material. For cyanobacteria this can be particularly challenging because of the presence of the cyanobacteria cell envelope. The great breath of cyanobacterial shape and size (unicellular, colonial, or filamentous multicellular) created a variety of cell lysis methods. However, there is still a lack of reliable techniques for nucleic acid extraction for several types of cyanobacteria. Here we designed and tested 15 extraction methods using physical, thermic or chemical stress on the filamentous cyanobacteria Planktothrix agardhii. Techniques based on the use of beads, sonication, and heat shock appeared to be too soft to break the Planktothrix agardhii cell envelope, whereas techniques based on the use of detergents degraded the cell envelope but also the RNA. Two protocols allowed to successfully obtain good-quality RNA. The first protocol consisted to manually crush the frozen cell pellet with a pestle and the second was based on the use of high-intensity ultra-sonication. When comparing these two, the high-intensity ultra-sonication protocol was less laborious, faster and allowed to extract 3.5 times more RNA compared to the liquid nitrogen pestle protocol. The high-intensity ultra-sonication protocol was then tested on five Planktothrix strains, this protocol allowed to obtain >8.5 μg of RNA for approximatively 3.5 × 108 cells. The extracted RNA were characterized by 260/280 and 260/230 ratio > to 2, indicating that the samples were devoid of contaminant, and RNA Quality Number > to 7, meaning that the integrity of RNA was preserved with this extraction method. In conclusion, the method we developed based on high-intensity ultra-sonication proved its efficacy in the extraction of Planktothrix RNA and could be helpful for other types of samples.

Microcystins (MCs) are the most commonly-reported hepatotoxins produced by various cyanobacterial taxa in fresh waters to constitute a potential threat to human and animal health. The biological role of MCs in the producer organisms is not known, and it would be very useful to understand the driving force behind the toxin production. Recent studies have suggested that MCs may have a protective function in cells facing environmental stress. Following this starting premise, we speculate that under adverse conditions the expression of stress-related genes coding for Heat Shock Proteins (Hsp) might be different in an MC-producing strain and its MC-deficient mutant. We therefore used RT-qPCR to compare the expression of 13 hsp genes of an MC-producing strain of Planktothrix agardhii (CYA126/8) and its MC-deficient ΔmcyD mutant over different periods of exposure to high light stress (HL). Three reference genes (RGs) were selected from six candidates to normalize the RT-qPCR data. Of these three RGs (rsh, rpoD, and gltA), gltA is used here for the first time as an RG in prokaryotes. Under HL stress, five genes were found to be strongly up-regulated in both strains (htpG, dnaK, hspA, groES, and groEL). Unexpectedly, we found that the MC-producing wild type strain accumulated higher levels of htpG and dnaK transcripts in response to HL stress than the MC-deficient mutant. In addition, a significant increase in the mcyE transcript was detected in the mutant, suggesting that MCs are required under HL conditions. We discuss several possible roles of MCs in the response to HL stress through their possible involvement in the protective mechanisms of the cells.

Selected strains of filamentous Phormidium-like cyanobacteria isolated from two Arctic regions (Ellesmere Island, High Canadian Arctic and Svalbard) and from Antarctica (Antarctic peninsula, South Shetland Islands and South Orkney Islands) were studied. The polyphasic approach used included phenotypic observations of morphological features and genotypic analyses (restriction fragment length polymorphism of 16S rRNA gene, internal transcribed space, 16S rRNA gene sequence analysis). Although genotypes generally correspond to observed morphotypes, the genetic analyses revealed a high degree of biodiversity that could not be unveiled using solely morphological evaluations. According to the phylogenetic analysis, the three clones were divided into two major clades, indicating that the phylogenetic distance between Arct-Ph5/Ant-Ph68 and Ant-Ph58 was so large they belonged to different genera. The polyphyletic position of strains of the genus Phormidium was confirmed by this study, attesting the need to entirely revise classification in this taxon in the future.

Microcystins (MCs) are the most commonly-reported hepatotoxins produced by various cyanobacterial taxa in fresh waters to constitute a potential threat to human and animal health. The biological role of MCs in the producer organisms is not known, and it would be very useful to understand the driving force behind the toxin production. Recent studies have suggested that MCs may have a protective function in cells facing environmental stress. Following this starting premise, we speculate that under adverse conditions the expression of stress-related genes coding for Heat Shock Proteins (Hsp) might be different in an MC-producing strain and its MC-deficient mutant. We therefore used RT-qPCR to compare the expression of 13 hsp genes of an MC-producing strain of Planktothrix agardhii (CYA126/8) and its MC-deficient [DELTA]mcyD mutant over different periods of exposure to high light stress (HL). Three reference genes (RGs) were selected from six candidates to normalize the RT-qPCR data. Of these three RGs (rsh, rpoD, and gltA), gltA is used here for the first time as an RG in prokaryotes. Under HL stress, five genes were found to be strongly up-regulated in both strains (htpG, dnaK, hspA, groES, and groEL). Unexpectedly, we found that the MC-producing wild type strain accumulated higher levels of htpG and dnaK transcripts in response to HL stress than the MC-deficient mutant. In addition, a significant increase in the mcyE transcript was detected in the mutant, suggesting that MCs are required under HL conditions. We discuss several possible roles of MCs in the response to HL stress through their possible involvement in the protective mechanisms of the cells.

Comte K., Coursin T. and Carre-Mlouka A. 2013. A new genotype in the genus Arthrospira (Oscillatoriales, Cyanobacteria) revealed by a mosaic-like structure of the 16S-23SrRNA intergenic spacer region in strain PCC 9901. Phycologia 52: 333-337. DOI: 10.2216/12-063.1 We examined the phylogenetic assignment of the Chinese strain PCC 9901, a cyanobacterium previously identified as Lyngbya laxespiralis, using phenotypic and molecular approaches. Phylogenetic analysis of the 16S rRNA gene sequence showed that strain PCC 9901 clustered with Arthrospira rather than Lyngbya. While all the Arthrospira strains were assigned to four genotypes (clusters IA, IB, IIA and IIB) based on the 16S-23S internal transcribed spacer (ITS) rRNA sequences, we reported here an unexpected new genotype for strain PCC 9901 that we named cluster III. A mosaic-like structure was found in two of the three intergenic spacer regions of the ITS (ISR1 and ISR3). In addition, a short repeated sequence was specific for genotype I, and a motif was found in genotype II sequences, but they were absent from the PCC 9901 ITS sequence, suggesting multiple recombination events and/or divergent evolution. Strain PCC 9901 was therefore placed into Arthrospira, and it constituted a new ITS cluster, together with other Asian strains.

Planktothrix agardhii is one of the freshwater cyanobacteria that can produce the hepatotoxin microcystins (MC)—a real threat to human and animal health. Knowledge of the biological role of MC in producing organisms is highly desired to understand the driving force of MC production. Recently, emerging evidences have suggested that MC may have protective role in cells facing environmental stress. If this is true, one should expect differences in the cellular protective mechanisms between MC-containing and MC-deficient mutant strains. To test this hypothesis, it would be essential to investigate the consequences of the loss of MC in Planktothrix in the transcriptional responses of its heat shock proteins (Hsps) to abiotic stresses—an important component of cellular stress response. However, a crucial first step is prerequisite for the isolation of hsp genes here, as the genome of Planktothrix has not been fully published. Therefore, we have successfully isolated four hsp genes including clpC (hsp100), htpG (hsp90), groEL (hsp60), and groES (hsp10) from Planktothrix agardhii PCC 7805 using ramped annealing PCR (RAN-PCR) with consensus-degenerate hybrid oligonucleotide primers (CODEHOP) and annealing control primer (ACP) system. In addition, some putative regulatory sequences found in the upstream region of groESL operon of Planktothrix agardhii were also discussed.

Uptake of several naturally occurring organic solutes by the unicellular cyanobacterium Microcystis sp. caused changes in cell turgor pressure (pt), which was determined by measuring the mean critical pressure (pc) of gas vesicles in the cells. Cells had an initial pt of 0.34 MPa, which decreased to 0.08 MPa in 0.15 M sucrose. In solutions of polyols, pt gradually recovered as the solutes penetrated the cytoplasmic membranes. From measurements of the exponential rate of turgor increase, cell volume and surface area, the permeability coefficient of the cytoplasmic membrane to each solute was calculated. Permeabilities to amino acids, ammonium ions and sodium acetate indicated little passive movement of these substances across the cell surface from solutions at high concentrations. We looked for evidence of ion trapping of acetic acid: at low pH there was a rapid rise in turgor pressure indicating a rapid uptake of this weak acid. After 20 min the turgor was lost, apparently due to loss of integrity of the cell membranes. For cells in natural habitats, studies of the permeability of cells to solutes is relevant to the problem of retaining substances that are accumulated by active uptake from solutions of low concentrations in natural waters.

Microcystins (MCs) are the most commonly-reported hepatotoxins produced by various cyanobacterial taxa in fresh waters to constitute a potential threat to human and animal health. The biological role of MCs in the producer organisms is not known, and it would be very useful to understand the driving force behind the toxin production. Recent studies have suggested that MCs may have a protective function in cells facing environmental stress. Following this starting premise, we speculate that under adverse conditions the expression of stress-related genes coding for Heat Shock Proteins (Hsp) might be different in an MC-producing strain and its MC-deficient mutant. We therefore used RT-qPCR to compare the expression of 13 hsp genes of an MC-producing strain of Planktothrix agardhii (CYA126/8) and its MC-deficient Delta mcyD mutant over different periods of exposure to high light stress (HL). Three reference genes (RGs) were selected from six candidates to normalize the RT-qPCR data. Of these three RGs (rsh, rpoD, and gltA), gltA is used here for the first time as an RG in prokaryotes. Under HL stress, five genes were found to be strongly up-regulated in both strains (htpG, dnaK, hspA, groES, and groEL). Unexpectedly, we found that the MC-producing wild type strain accumulated higher levels of htpG and dnaK transcripts in response to HL stress than the MC-deficient mutant. In addition, a significant increase in the mcyE transcript was detected in the mutant, suggesting that MCs are required under HL conditions. We discuss several possible roles of MCs in the response to HL stress through their possible involvement in the protective mechanisms of the cells.