An improvement in the (H2O)-O-18 technique for phytoplankton gross primary productivity (GPP), net primary productivity (NPP), and gross respiration (GR) is described that reduces cost, labor, and time over the traditional isotope ratio mass spectrometer (IRMS) method. Membrane inlet mass spectrometry (MIMS) was optimized to measure small (3 mL) samples with low isotope enrichment (1% O-18) and at high analytical precision (similar to 1 per mil). A photosynthetron was used to measure up to 10-point light curves of GPP, NPP, and GR using a total of 50 mL of sample water with an isotope cost of <$15 per experiment. A new incubation device is described, a Coronatron, that allows up to 12 samples with nutrient manipulation under uniform irradiance. Example light curves from highly contrasting natural water samples are presented that show elevated GPP relative to NPP and substantial light-stimulated GR. To highlight the improved method, examples nutrient manipulation curves are also presented showing GPP, NPP, and GR as a function of changes in ambient nitrate concentrations and different temperatures under constant light.
Abstract Paralytic shellfish toxins (PSTs) are produced by certain species of cyanobacteria and dinoflagellates. Part of the PST biosynthetic pathway has been elucidated in cyanobacteria, and the implication of some sxt genes has been confirmed by experimental studies. Contrary to cyanobacteria, knowledge about PST biosynthesis in dinoflagellates is more limited and generally restricted to comparative studies with the cyanobacterial pathway. To investigate the specificity of the PST pathway in dinoflagellates, 16 toxigenic and nontoxigenic Alexandrium minutum strains from a recombinant cross were compared, without prior assumption about genes or metabolites involved in PST synthesis, using an integrative approach combining untargeted metabolomic and transcriptomic data. Among the 60 most distinguishing transcripts between toxigenic and non‐toxigenic strains, only three sxt genes were present: sxt A4, sxt G, and sxt I. In contrast, non‐ sxt homologs were detected as highly discriminant between these two phenotypes. More specifically, a phy H homolog may act as the analog of the sxt S gene observed in cyanobacteria. Moreover, we identified four putative synthetic PST intermediates. Among these, Int‐C'2 correlated with the toxic phenotype, whereas three others were detected in both toxigenic and nontoxigenic strains, suggesting that these strains may share some parts of the biosynthetic pathway. Finally, our analyses identified both horizontally gained sxt genes and endogenous genes, including the candidate gene phy H, as candidate components of the PST biosynthetic pathway in A. minutum .
Abstract An improvement in the H 2 18 O technique for phytoplankton gross primary productivity (GPP), net primary productivity (NPP), and gross respiration (GR) is described that reduces cost, labor, and time over the traditional isotope ratio mass spectrometer (IRMS) method. Membrane inlet mass spectrometry (MIMS) was optimized to measure small (3 mL) samples with low isotope enrichment (1% 18 O) and at high analytical precision (~1 per mil). A photosynthetron was used to measure up to 10‐point light curves of GPP, NPP, and GR using a total of 50 mL of sample water with an isotope cost of <$15 per experiment. A new incubation device is described, a Coronatron, that allows up to 12 samples with nutrient manipulation under uniform irradiance. Example light curves from highly contrasting natural water samples are presented that show elevated GPP relative to NPP and substantial light‐stimulated GR. To highlight the improved method, examples nutrient manipulation curves are also presented showing GPP, NPP, and GR as a function of changes in ambient nitrate concentrations and different temperatures under constant light.
Giant kelp (Macrocystis pyrifera) forests have declined by 95% in Australia since the 1970s due to climate change. Despite expanding restoration efforts, long-term recovery is still lacking. Factors influencing recruitment by the microscopic gametophyte phase may represent a key mechanism underpinning the successful recovery and restoration of M. pyrifera. In the northern hemisphere, kelp gametophytes grow epiphytically and endophytically in red macroalgae and may represent an important "propagule bank" for kelp gametophyte recruitment. Our goal was to determine if M. pyrifera recruitment might depend on endo- or epiphytic gametophyte growth with understory red macroalgae on reefs in Tasmania, Australia. We first examined the composition and biomass of understory macroalgae living under kelp forests in Tasmania. We then tested if M. pyrifera gametophytes were located epiphytically or endophytically within specific red macroalgal hosts of 13 common species. Digital polymerase chain reaction (PCR) with M. pyrifera primers found M. pyrifera gametophytes in eight species of red macroalgae (Ballia callitricha, Gloiocladia halymenioides, Halopeltis australis, Phacelocarpus pepperocarpos, Plocamium angustum, Plocamium dilatatumi, Ptilonia australasica, and Ptilonia subulifera), with Ballia callitricha being the most common host (66.7% positive detections). By sterilizing the surface of host tissue, the detection of M. pyrifera DNA was consistent with endophytic occurrence of kelp gametophytes within the red macroalgal hosts but did not exclude the possibility that they also live epiphytically. These results suggest that red macroalgae may provide an important propagule bank for M. pyrifera gametophytes, and maintaining healthy understory assemblages may facilitate recovery and restoration efforts of M. pyrifera.
Abstract The taxonomy of heteropolar, tapering, and unbranched heterocytous cyanobacteria has undergone significant changes over time. Several novel species, genera, and families have been established using a polyphasic approach, which has provided a greater resolution in the systematics of these organisms. The Calotrichaceae, as of today, stands as a well‐resolved and monophyletic clade with at least five genera. The family has had some major revisions as well as additions. In addition, parameters such as the comparison of the 16S–23S ITS rRNA regions for the separation of one species from another have also grown and evolved and been amended recently within the genus Dulcicalothrix of the family Calotrichaceae. This approach has created the need to compare orthologous 16S–23S ITS rRNA region operons for better resolution at the species level. This study reviews the taxonomic advancements within the family Calotrichaceae with a discussion on the taxonomic status of the ambiguous positioning of the genus Neocalothrix and Phayaothrix . Considering the illegitimate status of Neocalothrix based on morphological, ecological, molecular, and phylogenetic evidence and the rules and recommendations of the International Code of Nomenclature for Algae, Fungi, and Plants , we have hereby transferred Neocalothrix to the existing genus Fulbrightiella and describe five novel species of Dulcicalothrix , viz. D. epiphytica , D. tripathii , D. acuminata , D. bombayensis , and D. goaensis from the Konkan region of India identified using a polyphasic approach.
