New or otherwise interesting desmid taxa from the Bangweulu region (Zambia). 1. Genera Micrasterias and Allorgeia (Desmidiales)

Background and aims - As for desmids, the Bangweulu wetlands in Zambia have turned out to belong to the most species-rich areas in Africa. Because of the scarce desmid literature dealing with those wetlands the present authors visited the region in question intending to increase our knowledge of African endemic species. Methods - Samples were collected from Lake Bangweulu and adjacent swamps as well as from Lake WakaWaka, a small isolated lake c. 150 km south-east of it. Collection was by squeezing submerged plant material or using a plankton net. Samples were partly immediately fixed for drawing desmid taxa later on, partly taken home alive for photographing and possible culturing. Key results -Two taxa are described as new to science: Micrasterias denboeri and M. radians var. cruxoides. M. truncata var. africana is raised to species level. Two varieties of M. tropica, i.e. var. elegans and var. elongata are split off as separate species. M. tropica var. crassa is recombined to M. robusta var. crassa. The asymmetric taxa M. sudanensis and Allorgeia incredibilis are discussed for their possible relationships. Conclusions - Most of the taxa discussed may be considered African endemics. Some of them, i.e. M. denboeri, M. sudanensis and Allorgeia incredibilis, presumably are even confined to the tropical central part of Africa. Most of the tropical records of M. crux-melitensis in literature probably have to be considered small forms of M. radians rather than to refer to European-North American M. crux-melitensis

Distributional patterns in some neotropical desmid species (Algae, Chlorophyta) in relation to migratory bird routes

La discussion est basée sur des échantillonnages réalisés par les auteurs en Colombie, et sur les données de la littérature. Des différences marquées entre la flore des Desmidiées tropicales d'Amérique Centrale et de l'ouest de L'Amérique du Sud, d'une part, et celle des bassins Orénoque-Amazone, d'autre part, suggèrent que les Andes limitent la distribution des algues d'eau douce en étant une barrière aux migrations des oiseaux aquatiques qui en sont les vecteurs potentiels. (Résumé d'auteur

Genome-wide diel growth state transitions in the diatom Thalassiosira pseudonana

Marine diatoms are important primary producers that thrive in diverse and dynamic environments. They do so, in theory, by sensing changing conditions and adapting their physiology accordingly. Using the model species Thalassiosira pseudonana, we conducted a detailed physiological and transcriptomic survey to measure the recurrent transcriptional changes that characterize typical diatom growth in batch culture. Roughly 40% of the transcriptome varied significantly and recurrently, reflecting large, reproducible cell-state transitions between four principal states: (i) "dawn," following 12 h of darkness; (ii ) "dusk," following 12 h of light; (iii ) exponential growth and nutrient repletion; and (iv) stationary phase and nutrient depletion. Increases in expression of thousands of genes at the end of the reoccurring dark periods (dawn), including those involved in photosynthesis (e.g., ribulose-1,5- bisphosphate carboxylase oxygenase genes rbcS and rbcL), imply large-scale anticipatory circadian mechanisms at the level of gene regulation. Repeated shifts in the transcript levels of hundreds of genes encoding sensory, signaling, and regulatory functions accompanied the four cell-state transitions, providing a preliminary map of the highly coordinated gene regulatory program under varying conditions. Several putative light sensing and signaling proteins were associated with recurrent diel transitions, suggesting that these genes may be involved in light-sensitive and circadian regulation of cell state. These results begin to explain, in comprehensive detail, how the diatom gene regulatory program operates under varying environmental conditions. Detailed knowledge of this dynamic molecular process will be invaluable for new hypothesis generation and the interpretation of genetic, environmental, and metatranscriptomic data from field studies

Fe limitation decreases transcriptional regulation over the diel cycle in the model diatom Thalassiosira pseudonana.

Iron (Fe) is an important growth factor for diatoms and its availability is further restricted by changes in the carbonate chemistry of seawater. We investigated the physiological attributes and transcriptional profiles of the diatom Thalassiosira pseudonana grown on a day: night cycle under different CO2/pH and iron concentrations, that in combination generated available iron (Fe\u27) concentrations of 1160, 233, 58 and 12 pM. We found the light-dark conditions to be the main driver of transcriptional patterns, followed by Fe\u27 concentration and CO2 availability, respectively. At the highest Fe\u27 (1160 pM), 55% of the transcribed genes were differentially expressed between day and night, whereas at the lowest Fe\u27 (12 pM), only 28% of the transcribed genes displayed comparable patterns. While Fe limitation disrupts the diel expression patterns for genes in most central metabolism pathways, the diel expression of light- signaling molecules and glycolytic genes was relatively robust in response to reduced Fe\u27. Moreover, we identified a non-canonical splicing of transcripts encoding triose-phosphate isomerase, a key-enzyme of glycolysis, generating transcript isoforms that would encode proteins with and without an active site. Transcripts that encoded an active enzyme maintained a diel expression at low Fe\u27, while transcripts that encoded the non-active enzyme lost the diel expression. This work illustrates the interplay between nutrient limitation and transcriptional regulation over the diel cycle. Considering that future ocean conditions will reduce the availability of Fe in many parts of the oceans, our work identifies some of the regulatory mechanisms that may shape future ecological communities

Staurastrum volans var. fuquenense nov. var., an interesting desmid taxon in the phytoplankton of laguna fúquene (colombia)

Of Staurastrum volans W. and amp; G. S. West, previously only known from Africa, a variety fuquenense COESEL is newly described from laguna Fúquene in the Colombian Andes. Judging from the ecological data of the localities in Colombia and from those recorded from African habitats, Staurastrum volans may be characterized ecologically as a planktonic desmid species that is well adapted to neutral to somewhat alkaline, eutrophic and unstable habitats.Se describe una nueva variedad de la laguna de Fuquene situada en los Andes de Colombia, perteneciente a la especie Staurastrum volans W. and amp; G. S. West, conocida hasta ahora solamente de Africa. A juzgar por los datos ecológicos de las localidades colombianas y de las registradas en los hábitat africanos, S. volans puede caracterizarse ecológicamente como una especie planctónica de desmidias, bien adaptada a medios eutróficos e inestables, cuyo pH osciló entre neutro a ligeramente alcalin

Diel transcriptional oscillations of light-sensitive regulatory elements in open-ocean eukaryotic plankton communities

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Coesel, S. N., Durham, B. P., Groussman, R. D., Hu, S. K., Caron, D. A., Morales, R. L., Ribalet, F., & Armbrust, E. V. Diel transcriptional oscillations of light-sensitive regulatory elements in open-ocean eukaryotic plankton communities. Proceedings of the National Academy of Sciences of the United States of America, 118(6), (2021): e2011038118, https://doi.org/10.1073./pnas.2011038118.The 24-h cycle of light and darkness governs daily rhythms of complex behaviors across all domains of life. Intracellular photoreceptors sense specific wavelengths of light that can reset the internal circadian clock and/or elicit distinct phenotypic responses. In the surface ocean, microbial communities additionally modulate nonrhythmic changes in light quality and quantity as they are mixed to different depths. Here, we show that eukaryotic plankton in the North Pacific Subtropical Gyre transcribe genes encoding light-sensitive proteins that may serve as light-activated transcription factors, elicit light-driven electrical/chemical cascades, or initiate secondary messenger-signaling cascades. Overall, the protistan community relies on blue light-sensitive photoreceptors of the cryptochrome/photolyase family, and proteins containing the Light-Oxygen-Voltage (LOV) domain. The greatest diversification occurred within Haptophyta and photosynthetic stramenopiles where the LOV domain was combined with different DNA-binding domains and secondary signal-transduction motifs. Flagellated protists utilize green-light sensory rhodopsins and blue-light helmchromes, potentially underlying phototactic/photophobic and other behaviors toward specific wavelengths of light. Photoreceptors such as phytochromes appear to play minor roles in the North Pacific Subtropical Gyre. Transcript abundance of environmental light-sensitive protein-encoding genes that display diel patterns are found to primarily peak at dawn. The exceptions are the LOV-domain transcription factors with peaks in transcript abundances at different times and putative phototaxis photoreceptors transcribed throughout the day. Together, these data illustrate the diversity of light-sensitive proteins that may allow disparate groups of protists to respond to light and potentially synchronize patterns of growth, division, and mortality within the dynamic ocean environment.This work was supported by a grant from the Simons Foundation (SCOPE Award 329108 [to E.V.A.]) and XSEDE Grant Allocation OCE160019 (to R.D.G.)