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1. Genome Sequence of the Estuarine Synechococcus sp. Strain NB0720_010

   https://doi.org/10.1128/mra.00151-22  

   MacKenzie, Campbell A.; Marston, Marcia F.; Tabima, Javier F.; Ahlgren, Nathan A. (August 2022, Microbiology Resource Announcements)

   Thrash, J. Cameron (Ed.)

   ABSTRACT Marine Synechococcus spp. are unicellular cyanobacteria widely distributed in the world’s oceans. We report the complete genome sequence of Synechococcus sp. strain NB0720_010, isolated from Narragansett Bay, Rhode Island. NB0702_10 has several large (>3,000-amino acid) protein-coding genes that may be important in its interactions with other cells, including grazers in estuarine habitats. 

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2. Draft Genome Sequence of the Cyanobacterium Synechococcus sp. Strain Nb3U1

   https://doi.org/10.1128/mra.00251-22  

   Pierpont, Christopher L.; Ohkubo, Satoshi; Miyashita, Hideaki; Miller, Scott R. (May 2022, Microbiology Resource Announcements)

   Maresca, Julia A. (Ed.)

   ABSTRACT We report the 3.5-Mb draft genome sequence of the cyanobacterium Synechococcus sp. strain Nb3U1, which was isolated from a microbial mat sample collected from Nakabusa Hot Spring, Nagano, Japan. 

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3. Dissolved organic phosphorus bond-class utilization by Synechococcus

   https://doi.org/10.1093/femsec/fiae099  

   Waggoner, Emily_M; Djaoudi, Kahina; Diaz, Julia_M; Duhamel, Solange (July 2024, FEMS Microbiology Ecology)

   Abstract Dissolved organic phosphorus (DOP) contains compounds with phosphoester, phosphoanhydride, and phosphorus–carbon bonds. While DOP holds significant nutritional value for marine microorganisms, the bioavailability of each bond-class to the widespread cyanobacterium Synechococcus remains largely unknown. This study evaluates bond-class specific DOP utilization by Synechococcus strains from open and coastal oceans. Both strains exhibited comparable growth rates when provided phosphate, a phosphoanhydride [3-polyphosphate and 45-polyphosphate], or a DOP compound with both phosphoanhydride and phosphoester bonds (adenosine 5′-triphosphate). Growth rates on phosphoesters [glucose-6-phosphate, adenosine 5′-monophosphate, bis(4-methylumbelliferyl) phosphate] were variable, and neither strain grew on selected phosphorus–carbon compounds. Both strains hydrolyzed 3-polyphosphate, then adenosine 5′-triphosphate, and lastly adenosine 5′-monophosphate, exhibiting preferential enzymatic hydrolysis of phosphoanhydride bonds. The strains’ exoproteomes contained phosphorus hydrolases, which combined with enhanced cell-free hydrolysis of 3-polyphosphate and adenosine 5′-triphosphate under phosphate deficiency, suggests active mineralization of phosphoanhydride bonds by these exoproteins. Synechococcus alkaline phosphatases presented broad substrate specificities, including activity toward the phosphoanhydride 3-polyphosphate, with varying affinities between strains. Collectively, these findings underscore the potentially significant role of compounds with phosphoanhydride bonds in Synechococcus phosphorus nutrition and highlight varied growth and enzymatic responses to molecular diversity within DOP bond-classes, thereby expanding our understanding of microbially mediated DOP cycling in marine ecosystems. 

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4. Co‐culture with Synechococcus facilitates growth of Prochlorococcus under ocean acidification conditions

   https://doi.org/10.1111/1462-2920.15277  

   Knight, Margaret_A; Morris, J_Jeffrey (October 2020, Environmental Microbiology)

   Summary Anthropogenic CO₂emissions are projected to lower the pH of the ocean 0.3 units by 2100. Previous studies suggested thatProchlorococcusandSynechococcus, the numerically dominant phytoplankton in the oceans, have different responses to elevated CO₂that may result in a dramatic shift in their relative abundances in future oceans. Here we showed that the exponential growth rates of these two genera respond to future CO₂conditions in a manner similar to other cyanobacteria, butProchlorococcusstrains had significantly lower realized growth rates under elevated CO₂regimes due to poor survival after exposure to fresh culture media. Despite this, aSynechococcusstrain was unable to outcompete aProchlorococcusstrain in co‐culture at elevated CO₂. Under these conditions,Prochlorococcus' poor response to elevated CO₂disappeared, andProchlorococcus'relative fitness showed negative frequency dependence, with both competitors having significant fitness advantages when initially rare. These experiments suggested that the two strains should be able to coexist indefinitely in co‐culture despite sharing nearly identical nutritional requirements. We speculate that negative frequency dependence exists due to reductive Black Queen evolution that has resulted in a passively mutualistic relationship analogous to that connectingProchlorococcuswith the ‘helper’ heterotrophic microbes in its environment. 

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5. Synechococcus nitrogen gene loss in iron-limited ocean regions

   https://doi.org/10.1038/s43705-023-00314-9  

   Sharpe, Garrett; Zhao, Liang; Meyer, Meredith G.; Gong, Weida; Burns, Shannon M.; Tagliabue, Allesandro; Buck, Kristen N.; Santoro, Alyson E.; Graff, Jason R.; Marchetti, Adrian; et al (October 2023, ISME Communications)

   Abstract Synechococcus are the most abundant cyanobacteria in high latitude regions and are responsible for an estimated 17% of annual marine net primary productivity. Despite their biogeochemical importance, Synechococcus populations have been unevenly sampled across the ocean, with most studies focused on low-latitude strains. In particular, the near absence of Synechococcus genomes from high-latitude, High Nutrient Low Chlorophyll (HNLC) regions leaves a gap in our knowledge of picocyanobacterial adaptations to iron limitation and their influence on carbon, nitrogen, and iron cycles. We examined Synechococcus populations from the subarctic North Pacific, a well-characterized HNLC region, with quantitative metagenomics. Assembly with short and long reads produced two near complete Synechococcus metagenome-assembled genomes (MAGs). Quantitative metagenome-derived abundances of these populations matched well with flow cytometry counts, and the Synechococcus MAGs were estimated to comprise >99% of the Synechococcus at Station P. Whereas the Station P Synechococcus MAGs contained multiple genes for adaptation to iron limitation, both genomes lacked genes for uptake and assimilation of nitrate and nitrite, suggesting a dependence on ammonium, urea, and other forms of recycled nitrogen leading to reduced iron requirements. A global analysis of Synechococcus nitrate reductase abundance in the TARA Oceans dataset found nitrate assimilation genes are also lower in other HNLC regions. We propose that nitrate and nitrite assimilation gene loss in Synechococcus may represent an adaptation to severe iron limitation in high-latitude regions where ammonium availability is higher. Our findings have implications for models that quantify the contribution of cyanobacteria to primary production and subsequent carbon export. 

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