More Like this

1. Heterotrophic Bacteria Dominate Catalase Expression during Microcystis Blooms

   https://doi.org/10.1128/aem.02544-21  

   Smith, Derek J. ; Berry, Michelle A. ; Cory, Rose M. ; Johengen, Thomas H. ; Kling, George W. ; Davis, Timothy W. ; Dick, Gregory J. ( July 2022 , Applied and Environmental Microbiology)

   Nojiri, Hideaki (Ed.)

   ABSTRACT In the oligotrophic oceans, key autotrophs depend on “helper” bacteria to reduce oxidative stress from hydrogen peroxide (H 2 O 2 ) in the extracellular environment. H 2 O 2 is also a ubiquitous stressor in freshwaters, but the effects of H 2 O 2 on autotrophs and their interactions with bacteria are less well understood in freshwaters. Naturally occurring H 2 O 2 in freshwater systems is proposed to impact the proportion of microcystin-producing (toxic) and non-microcystin-producing (nontoxic) Microcystis in blooms, which influences toxin concentrations and human health impacts. However, how different strains of Microcystis respond to naturally occurring H 2 O 2 concentrations and the microbes responsible for H 2 O 2 decomposition in freshwater cyanobacterial blooms are unknown. To address these knowledge gaps, we used metagenomics and metatranscriptomics to track the presence and expression of genes for H 2 O 2 decomposition by microbes during a cyanobacterial bloom in western Lake Erie in the summer of 2014. katG encodes the key enzyme for decomposing extracellular H 2 O 2 but was absent in most Microcystis cells. katG transcript relative abundance was dominated by heterotrophic bacteria. In axenic Microcystis cultures, an H 2 O 2 scavenger (pyruvate) significantly improved growth rates of one toxic strain while other toxic and nontoxic strains were unaffected. These results indicate that heterotrophic bacteria play a key role in H 2 O 2 decomposition in Microcystis blooms and suggest that their activity may affect the fitness of some Microcystis strains and thus the strain composition of Microcystis blooms but not along a toxic versus nontoxic dichotomy. IMPORTANCE Cyanobacterial harmful algal blooms (CHABs) threaten freshwater ecosystems globally through the production of toxins. Toxin production by cyanobacterial species and strains during CHABs varies widely over time and space, but the ecological drivers of the succession of toxin-producing species remain unclear. Hydrogen peroxide (H 2 O 2 ) is ubiquitous in natural waters, inhibits microbial growth, and may determine the relative proportions of Microcystis strains during blooms. However, the mechanisms and organismal interactions involved in H 2 O 2 decomposition are unexplored in CHABs. This study shows that some strains of bloom-forming freshwater cyanobacteria benefit from detoxification of H 2 O 2 by associated heterotrophic bacteria, which may impact bloom development. 

   more » « less
2. Emerging threats and persistent conservation challenges for freshwater biodiversity

   https://doi.org/10.1111/brv.12480  

   Reid, Andrea J. ; Carlson, Andrew K. ; Creed, Irena F. ; Eliason, Erika J. ; Gell, Peter A. ; Johnson, Pieter T. J. ; Kidd, Karen A. ; MacCormack, Tyson J. ; Olden, Julian D. ; Ormerod, Steve J. ; et al ( November 2018 , Biological Reviews)

   In the 12 years since Dudgeonet al. (2006) reviewed major pressures on freshwater ecosystems, the biodiversity crisis in the world's lakes, reservoirs, rivers, streams and wetlands has deepened. While lakes, reservoirs and rivers cover only 2.3% of the Earth's surface, these ecosystems host at least 9.5% of the Earth's described animal species. Furthermore, using the World Wide Fund for Nature's Living Planet Index, freshwater population declines (83% between 1970 and 2014) continue to outpace contemporaneous declines in marine or terrestrial systems. The Anthropocene has brought multiple new and varied threats that disproportionately impact freshwater systems. We document 12 emerging threats to freshwater biodiversity that are either entirely new since 2006 or have since intensified: (i) changing climates; (ii) e‐commerce and invasions; (iii) infectious diseases; (iv) harmful algal blooms; (v) expanding hydropower; (vi) emerging contaminants; (vii) engineered nanomaterials; (viii) microplastic pollution; (ix) light and noise; (x) freshwater salinisation; (xi) declining calcium; and (xii) cumulative stressors. Effects are evidenced for amphibians, fishes, invertebrates, microbes, plants, turtles and waterbirds, with potential for ecosystem‐level changes through bottom‐up and top‐down processes. In our highly uncertain future, the net effects of these threats raise serious concerns for freshwater ecosystems. However, we also highlight opportunities for conservation gains as a result of novel management tools (e.g. environmental flows, environmental DNA) and specific conservation‐oriented actions (e.g. dam removal, habitat protection policies, managed relocation of species) that have been met with varying levels of success. Moving forward, we advocate hybrid approaches that manage fresh waters as crucial ecosystems for human life support as well as essential hotspots of biodiversity and ecological function. Efforts to reverse global trends in freshwater degradation now depend on bridging an immense gap between the aspirations of conservation biologists and the accelerating rate of species endangerment.

    

   more » « less
3. Cylindrospermopsis raciborskii Virus and host: genomic characterization and ecological relevance

   https://doi.org/10.1111/1462-2920.14425  

   Martin, Robbie M. ; Moniruzzaman, Mohammad ; Mucci, Nicholas C. ; Willis, Anusuya ; Woodhouse, Jason N. ; Xian, Yuejiao ; Xiao, Chuan ; Brussaard, Corina P. D. ; Wilhelm, Steven W. ( October 2018 , Environmental Microbiology)

   Cylindrospermopsis (Raphidiopsis) raciborskiiis an invasive, filamentous, nitrogen‐fixing cyanobacterium that forms frequent blooms in freshwater habitats. While viruses play key roles in regulating the abundance, production and diversity of their hosts in aquatic ecosystems, the role(s) of viruses in the ecology ofC. raciborskiiis almost unexplored. Progress in this field has been hindered by the absence of a characterized virus–host system inC. raciborskii. To bridge this gap, we sequenced the genome of CrV‐01T, a previously isolated cyanosiphovirus, and its host,C. raciborskiistrain Cr2010. Analyses suggest that CrV‐01T represents a distinct clade of siphoviruses infecting, and perhaps lysogenizing, filamentous cyanobacteria. Its genome contains unique features that include an intact CRISPR array and a 12 kb inverted duplication. Evidence suggests CrV‐01T recently gained the ability to infect Cr2010 and recently lost the ability to form lysogens. The cyanobacterial host contains a CRISPR‐Cas system with CRISPR spacers matching protospacers within the inverted duplication of the CrV‐01T genome. Examination of metagenomes demonstrates that viruses with high genetic identity to CrV‐01T, but lacking the inverted duplication, are present inC. raciborskiiblooms in Australia. The unique genomic features of the CrV/Cr2010 system offers opportunities to investigate in more detail virus–host interactions in an ecologically important bloom‐forming cyanobacterium.

    

   more » « less
4. 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
5. Carboxysome Mispositioning Alters Growth, Morphology, and Rubisco Level of the Cyanobacterium Synechococcus elongatus PCC 7942

   https://doi.org/10.1128/mBio.02696-20  

   Rillema, Rees ; Hoang, Y ; MacCready, Joshua S. ; Vecchiarelli, Anthony G. ( August 2021 , mBio)

   Komeili, Arash (Ed.)

   ABSTRACT Cyanobacteria are the prokaryotic group of phytoplankton responsible for a significant fraction of global CO 2 fixation. Like plants, cyanobacteria use the enzyme ribulose 1,5-bisphosphate carboxylase/oxidase (Rubisco) to fix CO 2 into organic carbon molecules via the Calvin-Benson-Bassham cycle. Unlike plants, cyanobacteria evolved a carbon-concentrating organelle called the carboxysome—a proteinaceous compartment that encapsulates and concentrates Rubisco along with its CO 2 substrate. In the rod-shaped cyanobacterium Synechococcus elongatus PCC 7942, we recently identified the McdAB system responsible for uniformly distributing carboxysomes along the cell length. It remains unknown what role carboxysome positioning plays with respect to cellular physiology. Here, we show that a failure to distribute carboxysomes leads to slower cell growth, cell elongation, asymmetric cell division, and elevated levels of cellular Rubisco. Unexpectedly, we also report that even wild-type S. elongatus undergoes cell elongation and asymmetric cell division when grown at the cool, but environmentally relevant, growth temperature of 20°C or when switched from a high- to ambient-CO 2 environment. The findings suggest that carboxysome positioning by the McdAB system functions to maintain the carbon fixation efficiency of Rubisco by preventing carboxysome aggregation, which is particularly important under growth conditions where rod-shaped cyanobacteria adopt a filamentous morphology. IMPORTANCE Photosynthetic cyanobacteria are responsible for almost half of global CO 2 fixation. Due to eutrophication, rising temperatures, and increasing atmospheric CO 2 concentrations, cyanobacteria have gained notoriety for their ability to form massive blooms in both freshwater and marine ecosystems across the globe. Like plants, cyanobacteria use the most abundant enzyme on Earth, Rubisco, to provide the sole source of organic carbon required for its photosynthetic growth. Unlike plants, cyanobacteria have evolved a carbon-concentrating organelle called the carboxysome that encapsulates and concentrates Rubisco with its CO 2 substrate to significantly increase carbon fixation efficiency and cell growth. We recently identified the positioning system that distributes carboxysomes in cyanobacteria. However, the physiological consequence of carboxysome mispositioning in the absence of this distribution system remains unknown. Here, we find that carboxysome mispositioning triggers changes in cell growth and morphology as well as elevated levels of cellular Rubisco. 

   more » « less