More Like this

1. Microcystins in planktonic and benthic food web components from Greenlandic lakes

   https://doi.org/10.1002/ecs2.3539  

   Trout‐Haney, Jessica V. ; Cottingham, Kathryn L. ( June 2021 , Ecosphere)

   There is increasing global concern regarding the social, economic, human health, and environmental health implications of cyanotoxins. However, much of what we know about cyanotoxins comes from studies of temperate or tropical systems with conspicuous surface blooms of cyanobacteria. We measured the concentrations of microcystins (MCs), potent cyanotoxins produced by many cyanobacterial taxa, within lake food webs in southwestern Greenland. We detected MCs in six taxonomic groups of organisms and found that median MC concentrations in large (>50 µm) phytoplankton were an order of magnitude higher than benthic cyanobacteria (genusNostoc) and two orders of magnitude higher than benthic grazers and consumers (snails, dytiscid larvae, and chironomid larvae). Microcystin concentrations generally decreased with increasing trophic position, suggesting that biomagnification does not occur in these lakes. We conclude that MCs are prevalent in multiple components of these Arctic aquatic food webs and that both benthic and pelagic taxa may be sources of MCs.

    

   more » « less
2. A Tripartite, Hierarchical Sigma Factor Cascade Promotes Hormogonium Development in the Filamentous Cyanobacterium Nostoc punctiforme

   https://doi.org/10.1128/mSphere.00231-19  

   Gonzalez, Alfonso ; Riley, Kelsey W. ; Harwood, Thomas V. ; Zuniga, Esthefani G. ; Risser, Douglas D. ( June 2019 , mSphere)

   ABSTRACT Cyanobacteria are prokaryotes capable of oxygenic photosynthesis, and frequently, nitrogen fixation as well. As a result, they contribute substantially to global primary production and nitrogen cycles. Furthermore, the multicellular filamentous cyanobacteria in taxonomic subsections IV and V are developmentally complex, exhibiting an array of differentiated cell types and filaments, including motile hormogonia, making them valuable model organisms for studying development. To investigate the role of sigma factors in the gene regulatory network (GRN) controlling hormogonium development, a combination of genetic, immunological, and time-resolved transcriptomic analyses were conducted in the model filamentous cyanobacterium Nostoc punctiforme , which, unlike other common model cyanobacteria, retains the developmental complexity of field isolates. The results support a model where the hormogonium GRN is driven by a hierarchal sigma factor cascade, with sigJ activating the expression of both sigC and sigF, as well as a substantial portion of additional hormogonium-specific genes, including those driving changes to cellular architecture. In turn, sigC regulates smaller subsets of genes for several processes, plays a dominant role in promoting reductive cell division, and may also both positively and negatively regulate sigJ to reinforce the developmental program and coordinate the timing of gene expression, respectively. In contrast, the sigF regulon is extremely limited. Among genes with characterized roles in hormogonium development, only pilA shows stringent sigF dependence. For sigJ -dependent genes, a putative consensus promoter was also identified, consisting primarily of a highly conserved extended −10 region, here designated a J-Box, which is widely distributed among diverse members of the cyanobacterial lineage. IMPORTANCE Cyanobacteria are integral to global carbon and nitrogen cycles, and their metabolic capacity coupled with their ease of genetic manipulation make them attractive platforms for applications such as biomaterial and biofertilizer production. Achieving these goals will likely require a detailed understanding and precise rewiring of these organisms’ GRNs. The complex phenotypic plasticity of filamentous cyanobacteria has also made them valuable models of prokaryotic development. However, current research has been limited by focusing primarily on a handful of model strains which fail to reflect the phenotypes of field counterparts, potentially limiting biotechnological advances and a more comprehensive understanding of developmental complexity. Here, using Nostoc punctiforme , a model filamentous cyanobacterium that retains the developmental range of wild isolates, we define previously unknown definitive roles for a trio of sigma factors during hormogonium development. These findings substantially advance our understanding of cyanobacterial development and gene regulation and could be leveraged for future applications. 

   more » « less
3. Environmental Factors Impacting the Development of Toxic Cyanobacterial Proliferations in a Central Texas Reservoir

   https://doi.org/10.3390/toxins16020091  

   Perri, Katherine A. ; Bellinger, Brent J. ; Ashworth, Matt P. ; Manning, Schonna R. ( February 2024 , Toxins)

   Cyanobacterial harmful algal proliferations (cyanoHAPs) are increasingly associated with dog and livestock deaths when benthic mats break free of their substrate and float to the surface. Fatalities have been linked to neurotoxicosis from anatoxins, potent alkaloids produced by certain genera of filamentous cyanobacteria. After numerous reports of dog illnesses and deaths at a popular recreation site on Lady Bird Lake, Austin, Texas in late summer 2019, water and floating mat samples were collected from several sites along the reservoir. Water quality parameters were measured and mat samples were maintained for algal isolation and DNA identification. Samples were also analyzed for cyanobacterial toxins using LC-MS. Dihydroanatoxin-a was detected in mat materials from two of the four sites (0.6–133 ng/g wet weight) while water samples remained toxin-free over the course of the sampling period; no other cyanobacterial toxins were detected. DNA sequencing analysis of cyanobacterial isolates yielded a total of 11 genera, including Geitlerinema, Tyconema, Pseudanabaena, and Phormidium/Microcoleus, taxa known to produce anatoxins, including dihydroanatoxin, among other cyanotoxins. Analyses indicate that low daily upriver dam discharge, higher TP and NO3 concentrations, and day of the year were the main parameters associated with the presence of toxic floating cyanobacterial mats.

    

   more » « less
4. Two duckweed species exhibit variable tolerance to microcystin-LR exposure across genotypic lineages

   https://doi.org/10.1016/j.hal.2023.102548  

   Rzodkiewicz, Lacey D. ; Turcotte, Martin M. ( January 2024 , Harmful Algae)

   Cyanotoxins produced by harmful cyanobacteria blooms can damage freshwater ecosystems and threaten human health. Floating macrophytes may be used as a means of biocontrol by limiting light and resources available to cyanobacteria. However, genetic variation in macrophyte sensitivity to cyanotoxins could influence their suit- ability as biocontrol agents. We investigated the influence of such intraspecific variation on the response of two rapidly growing duckweed species, Lemna minor and Spirodela polyrhiza, often used in nutrient and metal bioremediation. We assessed two biomarkers related to productivity (biomass and chlorophyll A production) and two related to fitness measures (population size and growth rate). Fifteen genetic lineages of each species were grown in media containing common cyanotoxin microcystin-LR at ecologically relevant concentrations or control media for a period of twelve days. Genotype identity had a strong impact on all biomarker responses. Microcystin concentration slightly increased the final population sizes of both macrophyte species with a marginal effect on growth rate of L. minor and the chlorophyll A production of S. polyrhiza, but overall these species were very tolerant of microcystin. The strong tolerance supports the potential use of these plants as bioremediators of cyanobacterial blooms. However, differential impact of microcystin exposure discovered in single lineage models among genotypes indicates a potential for cyanotoxins to act as selective forces, necessitating attention to genotype selection for bioremediation. 

   more » « less
5. Predicting the effects of climate change on freshwater cyanobacterial blooms requires consideration of the complete cyanobacterial life cycle

   https://doi.org/10.1093/plankt/fbaa059  

   Cottingham, Kathryn L. ; Weathers, Kathleen C. ; Ewing, Holly A. ; Greer, Meredith L. ; Carey, Cayelan C. ; Moisander, ed., Pia ( December 2020 , Journal of Plankton Research)

   To date, most research on cyanobacterial blooms in freshwater lakes has focused on the pelagic life stage. However, examining the complete cyanobacterial life cycle—including benthic life stages—may be needed to accurately predict future bloom dynamics. The current expectation, derived from the pelagic life stage, is that blooms will continue to increase due to the warmer temperatures and stronger stratification associated with climate change. However, stratification and mixing have contrasting effects on different life stages: while pelagic cyanobacteria benefit from strong stratification and are adversely affected by mixing, benthic stages can benefit from increased mixing. The net effects of these potentially counteracting processes are not yet known, since most aquatic ecosystem models do not incorporate benthic stages and few empirical studies have tracked the complete life cycle over multiple years. Moreover, for many regions, climate models project both stronger stratification and increased storm-induced mixing in the coming decades; the net effects of those physical processes, even on the pelagic life stage, are not yet understood. We therefore recommend an integrated research agenda to study the dual effects of stratification and mixing on the complete cyanobacterial life cycle—both benthic and pelagic stages—using models, field observations and experiments.

    

   more » « less