Assessment of nitrogen fixation rates in the Laurentian Great Lakes

Natwora, Kaela E.; Sheik, Cody S.

doi:10.1016/j.jglr.2021.07.005

Cited by 13 publications

(8 citation statements)

References 49 publications

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“…We observed differential expression of various genes involved in N-fixation across time and space in western Lake Erie. This finding, along with previously reported expression of nifH (Steffen et al, 2015) and fixation of N in western Lake Erie (Natwora and Sheik, 2021), challenge the notion that current western Lake Erie cyanoHABs do not contain N-fixers (Barnard et al, 2021;Newell et al, 2019). Our results also suggest that the ADA taxa are the primary or sole N-fixers in western Lake Erie, in contrast to Sandusky Bay where N fixation has been attributed to both cyanobacteria and heterotrophic bacteria (Davis et al, 2015).…”

Section: Dolichospermum Spp Can Also Dominate Great Lakes Cyanohabs F...supporting

confidence: 79%

Transcriptionally active nitrogen fixation and biosynthesis of diverse secondary metabolites by Dolichospermum and Aphanizominom-like Cyanobacteria in western Lake Erie Microcystis blooms

Yancey

Mathiesen

Dick

2022

Preprint

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Cyanobacterial harmful algal blooms (cyanoHABs) in the western basin of Lake Erie are dominated by microcystin producing Microcystis spp., but other cyanobacterial taxa that coexist in these communities may play important roles in production of toxins and shaping bloom dynamics and community function. In this study, we used metagenomic and metatranscriptomic data from the 2014 western Lake Erie cyanoHAB to explore the genetic diversity and biosynthetic potential of cyanobacteria belonging to the Anabaena, Dolichospermum, Aphanizomenon (ADA) clade. We reconstructed two near-complete metagenome-assembled genomes from two distinct ADA clade species, each containing biosynthetic gene clusters that encode novel and known secondary metabolites that were transcriptionally active. These taxa also appear to have varying nutrient acquisition strategies, and their ability to fix N may be important for synthesizing N rich metabolites as well as supporting bloom persistence. Although not the dominant organism in this system, these results suggest that ADA may be important community members in western Lake Erie cyanoHABs that have the potential to produce unmonitored toxins.

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Section: Dolichospermum Spp Can Also Dominate Great Lakes Cyanohabs F...supporting

confidence: 79%

Transcriptionally active nitrogen fixation and biosynthesis of diverse secondary metabolites by Dolichospermum and Aphanizominom-like Cyanobacteria in western Lake Erie Microcystis blooms

Yancey

Mathiesen

Dick

2022

Preprint

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“…Potential nitrogen fixation rates were quantified using the acetylene reduction assay (ARA) method, previously described in (Natwora & Sheik, 2021). The ARA quantifies the conversion of acetylene gas to ethylene gas by the nitrogenase enzyme (Christiansen et al, 2000;Stewart et al, 1967).…”

Section: Assessing Nitrogen Fixation Rates Using the Acetylene Reduct...mentioning

confidence: 99%

“…blooms and can produce a surplus of free N (Hoffman et al 2022). While heterotrophic release of N is important, nitrogen fixation, a microbial mediated process in which atmospheric nitrogen (N2) is fixed to ammonia (NH3), can be a significant and underappreciated source of bioavailable ammonia in lakes (Natwora & Sheik, 2021) and in cyanobacterial blooms (Beversdorf et al, 2013). Together this highlights that biological nitrogen cycling is highly important to the maintenance and duration of cHABs.…”

Section: Introductionmentioning

confidence: 99%

“…In Lake Erie, up to 85% of N2 fixed through nitrogen fixation leads to N assimilation in the cell or to the surrounding microbial community (Salk et al, 2018). Recent work has shown that across the Laurentian Great Lakes nitrogen fixation is an important process (Natwora & Sheik, 2021). The influence nitrogen fixation has on eutrophication is especially evident in freshwater bodies that hold dense diazotrophic (nitrogen fixing microorganisms) populations that contribute to the sustainably of available nitrogen (Scott & Marcarelli, 2012;Wurtsbaugh et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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Nitrogen dynamics and fixation control cyanobacterial abundance, diversity, and toxicity in Lake of the Woods (USA, Canada)

Natwora

Heathcote

Edlund

et al. 2023

Preprint

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Our understanding of drivers of cyanobacterial harmful algal blooms (cHABs) is evolving, but it is apparent that not all lakes are created equal. Nitrogen (N) is an important component of all cHABs and is crucial for cyanotoxin production. It is generally assumed that external nitrogen inputs are the primary N source for cHABs. However, in northern lakes, nitrogen inputs are typically low which suggests that internal nitrogen cycling, through heterotrophic organic matter decomposition or nitrogen fixation, may play a significant role in cHAB development and sustainment. Using Lake of the Woods as a testbed, we quantified nutrients, cyanotoxins, nitrogen fixation, and the microbial community in the southern extent of the lake. During our temporal study, inorganic nitrogen species (NO3-+NO2- and NH4+) were either at very low concentrations or below detection, while phosphorus was in excess. These conditions resulted in nitrogen-deficient growth and thereby favored nitrogen-fixing cyanobacterial species. In response, nitrogen fixation rates increased exponentially throughout the summer and coincided with the Aphanizomenon sp. bloom. Despite nitrogen limitation, microcystin, anatoxin, saxitoxin, and cylindrospermopsin were all detected, with microcystin being the most abundant cyanotoxin detected. Microcystin concentrations were highest when free nitrogen was available and coincided with an increase in Microcystis. Together, our work suggests that internal nitrogen dynamics are responsible for the dominance of nitrogen-fixing cyanobacteria and that additions of nitrogen may increase the likelihood of other cyanobacterial species, currently at low abundance, to increase growth and cyanotoxin production.

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“…Similarly, diazotrophic cyanobacteria are thought to gain a unique advantage in N‐limited systems (Harke et al, 2016; Hayes et al, 2015). Measurable N‐fixation under N‐replete, P‐limited conditions (Miller et al, 2013; Natwora & Sheik, 2021; Paerl & Otten, 2016), however, challenges the deterministic coupling of this physiological adaptation to broad stoichiometric gradients and highlights the functional diversity that can exist within aquatic microbial assemblages, including consortia dominated by cyanobacteria.…”

Section: The Paradox Of Cyanobacterial Proliferationmentioning

confidence: 99%

Paradox versus paradigm: A disconnect between understanding and management of freshwater cyanobacterial harmful algae blooms

et al. 2022

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Freshwater cyanobacterial harmful algae blooms (cHABs) are a major threat to human and environmental health and are increasing globally in frequency and severity. To manage this threat in a timely manner, science must focus on increasing our ability to predict the growth and toxigenicity of specific taxa of cyanobacteria. Recent molecular research has revealed striking genomic and metabolic diversity among the many morphologically indistinguishable sub‐species and strains of cyanobacteria. Assemblage‐level molecular metabolic capability surveys promise to improve our ability to predict cyanobacterial responses to environmental forcing, but many of these cutting‐edge techniques are not widely available or cost‐effective enough to be employed in routine monitoring programmes to support management decisions. Taxonomic ambiguity, cryptic functional specialisation, incongruence between genomic capability and phylogeny, and genomic flexibility impose severe challenges to our ability to ascribe autecological attributes at a level of taxonomic resolution that is attainable under current management strategies (i.e. Linnaean species). This lack of knowledge prohibits reliable predictions of species' responses to environmental stressors. Cyanobacterial species comprise consortia of metabolically diverse, morphologically indistinct strains that span a range of ecological specialisation. Under current, broadly applied taxonomic concepts, these species functionally embody a generalist ecological strategy—persisting and/or proliferating where other specialised competitors are negatively impacted. We postulate that within current management frameworks, characterising of cyanobacterial species as competing generalists, as well as considering abundance trajectories of well‐characterised, non‐cyanobacterial specialist phytoplankton will generate more scalable, mechanistic, and management‐relevant insight into increasing cHAB frequency and severity in suitable time frames. Here we recommend that cHAB management considers the competitive framework of phytoplankton communities, including cyanobacteria, wherein diverse environmental changes lead to deterministic responses by readily identifiable, documented specialist taxa. Characterising these changes in community structure will quantify the relative importance of altered stressors and resource availability that can be exploited by metabolically flexible cyanobacteria.

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Assessment of nitrogen fixation rates in the Laurentian Great Lakes

Cited by 13 publications

References 49 publications

Transcriptionally active nitrogen fixation and biosynthesis of diverse secondary metabolites by Dolichospermum and Aphanizominom-like Cyanobacteria in western Lake Erie Microcystis blooms

Transcriptionally active nitrogen fixation and biosynthesis of diverse secondary metabolites by Dolichospermum and Aphanizominom-like Cyanobacteria in western Lake Erie Microcystis blooms

Nitrogen dynamics and fixation control cyanobacterial abundance, diversity, and toxicity in Lake of the Woods (USA, Canada)

Paradox versus paradigm: A disconnect between understanding and management of freshwater cyanobacterial harmful algae blooms

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