Arnoldo Font Nájera
Karina Yew_Hoong Gin
Jennifer L. Graham
Dominik Strapagiel
Rebecca M. Gorney
Jerome Wai Kok
Shu Harn Te
Magdalena Kluska
Milena Skóra
Michał Seweryn
Francisco Josue Hun
Joanna Mankiewicz-Boczek
2025
<p><span>Cyanobacterial toxicity, cyanotoxins, and their impact on aquatic ecosystems and human health are well documented. In comparison, less is known about bloom-associated bacterial communities. Co-occurring bacteria can influence bloom development, physiology and collapse, and may also provide a niche for pathogenic bacteria. Existing research focuses on the cyanosphere of </span><i>Microcystis</i><span>-dominated blooms, despite the increasing prevalence of filamentous genera (</span><i>Aphanizomenon</i><span> and </span><i>Planktothrix</i><span>). This pilot study aimed to broaden our understanding of the bacterial consortia attached to morphologically distinct cyanobacteria (coccoid and filamentous) dominating phytoplankton communities and to explore their potential roles in amplifying the impacts of cyanobacterial blooms. We investigated four shallow freshwater bodies across three continents and two climate zones: an urban pond in the USA, a dammed reservoir and a natural lake in Poland, and an urban water body in Singapore. Amplicon sequencing (16S rRNA gene) was used to characterize bacterial communities, while shotgun metagenomics identified nitrogen- and phosphorus-cycling genes to infer potential eco-physiological functions. Cyanobacteria dominated bacterioplankton assemblages at all sites (>35.6%), with bloom composition influencing toxigenic profiles. A mixed bloom of </span><i>Microcystis</i><span>, </span><i>Snowella</i><span>, and </span><i>Aphanizomenon</i><span> had the broadest range of cyanotoxin synthetase genes (</span><i>mcy</i><span>E, </span><i>cyr</i><span>J, </span><i>ana</i><span>F and </span><i>sxt</i><span>A). </span><i>Microcystis</i><span> blooms correlated with increased </span><i>Roseomonas</i><span>, while </span><i>Planktothrix</i><span> co-occurred with </span><i>Flavobacterium</i><span> – both bacteria likely contribute to nutrient-cycling within blooms and represent potential opportunistic pathogens for aquatic organisms and humans. The </span><i>Microcystis</i><span> cyanosphere exhibited the highest number of significant positive correlations with bacteria (19 relations), compared to </span><i>Planktothrix</i><span> and </span><i>Aphanizomenon</i><span> (11 and 2 relations, respectively). Non-diazotrophic blooms of </span><i>Microcystis</i><span> and </span><i>Planktothrix</i><span> showed greater abundances of nitrogen – (</span><i>ure</i><span>B, </span><i>gln</i><span>A, </span><i>nar</i><span>B, and </span><i>nar</i><span>HZ) and phosphorus-cycling genes (</span><i>pho</i><span>BHPR and </span><i>ppk</i><span>1), indicating a strong dependence on associated bacteria for nutrient acquisition compared to diazotrophic </span><i>Aphanizomenon</i><span>. These findings suggest that </span><i>Aphanizomenon</i><span>-dominated blooms may be sustained by simpler microbiomes. Our results provide preliminary evidence of cyanosphere heterogeneity potentially shaped by the dominance or coexistence of three morphologically and eco-physiologically distinct genera of cyanobacteria. A comprehensive knowledge of the taxonomy and functional roles of bloom-associated microbiomes is therefore essential to understand bloom activity, evaluate the environmental threat, and develop effective strategies for prevention and mitigation.</span></p>
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10.3389/fmicb.2025.1655370
en
Frontiers Media
Bacterial community diversity and potential eco-physiological roles in toxigenic blooms composed of Microcystis, Aphanizomenon or Planktothrix
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