Spatial Distribution, Diversity, and Activity of Microbial Phototrophs in the Baltic Sea

Xu, Peihang; Reeder, Christian Furbo; Löscher, Carolin R.

doi:10.3389/fmars.2021.773210

Cited by 3 publications

(1 citation statement)

References 93 publications

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“…and Crocosphaera sp., has related the nifH gene to N 2 O fixation 5 . Since being set up in 2005, our nitrogen-limited ponds have developed diverse diazotroph communities 42 , comparable to those in estuaries 54 , freshwater 55 and seawater 56 . Here we set out to link cause to effect by attempting to enrich N 2 O fixing candidates but failed to detect any changes in the total nifH community after 25 days enrichment with N 2 O (Supplementary Fig.…”

Section: Discussionmentioning

confidence: 99%

Direct biological fixation provides a freshwater sink for N2O

Si,

Zhu,

Sanders

et al. 2023

Nat Commun

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Nitrous oxide (N2O) is a potent climate gas, with its strong warming potential and ozone-depleting properties both focusing research on N2O sources. Although a sink for N2O through biological fixation has been observed in the Pacific, the regulation of N2O-fixation compared to canonical N2-fixation is unknown. Here we show that both N2O and N2 can be fixed by freshwater communities but with distinct seasonalities and temperature dependencies. N2O fixation appears less sensitive to temperature than N2 fixation, driving a strong sink for N2O in colder months. Moreover, by quantifying both N2O and N2 fixation we show that, rather than N2O being first reduced to N2 through denitrification, N2O fixation is direct and could explain the widely reported N2O sinks in natural waters. Analysis of the nitrogenase (nifH) community suggests that while only a subset is potentially capable of fixing N2O they maintain a strong, freshwater sink for N2O that could be eroded by warming.

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Section: Discussionmentioning

confidence: 99%

Direct biological fixation provides a freshwater sink for N2O

Si,

Zhu,

Sanders

et al. 2023

Nat Commun

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Biodiversity of microorganisms in the Baltic Sea: the power of novel methods in the identification of marine microbes

Mazur-Marzec,

Andersson,

Błaszczyk

et al. 2024

FEMS Microbiology Reviews

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Until recently, the data on the diversity of the entire microbial community from the Baltic Sea were relatively rare and very scarce. However, modern molecular methods have provided new insights into this field with interesting results. They can be summarized as follows. (i) Although low salinity causes a reduction in the biodiversity of multicellular species relative to the populations of the North-East Atlantic, no such reduction occurs in bacterial diversity. (ii) Among cyanobacteria, the picocyanobacterial group dominates when considering gene abundance, while filamentous cyanobacteria dominate in means of biomass. (iii) The diversity of diatoms and dinoflagellates is significantly larger than described a few decades ago; however, molecular studies on these groups are still scarce. (iv) Knowledge gaps in other protistan communities are evident. (v) Salinity is the main limiting parameter of pelagic fungal community composition, while the benthic fungal diversity is shaped by water depth, salinity, and sediment C and N availability. (vi) Bacteriophages are the predominant group of viruses, while among viruses infecting eukaryotic hosts, Phycodnaviridae are the most abundant; the Baltic Sea virome is contaminated with viruses originating from urban and/or industrial habitats. These features make the Baltic Sea microbiome specific and unique among other marine environments.

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Biofilm formation and cell plasticity drive diazotrophy in an anoxygenic phototrophic bacterium

Fernández-Juárez,

Hallstrøm,

Pacherres

et al. 2023

Appl Environ Microbiol

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Non-cyanobacterial diazotrophs (NCDs) are widespread and active in marine waters. The carbon and low-oxygen (O 2 ) conditions required for their N 2 fixation may be encountered on marine particles, while a putative role of light remains uninvestigated. This study explored factors that regulate N 2 fixation in Rhodopseudomonas sp. BAL398—a anoxygenic phototrophic bacterium isolated from low-salinity surface waters. Light (250 µmol photons m −2 s −1 ) and anoxia (0 µM O 2 ) stimulated growth and N 2 fixation; however, diazotrophy in light was dependent on high organic carbon levels (35 mM, glucose:succinate). Immunolabeling revealed that cellular nitrogenase levels increased with light, decreasing inorganic nitrogen (N) and ambient O 2 (250 µM). Light and O 2 stimulated motility and biofilm formation on surfaces, and N 2 fixation rates increased compared to the control treatment. N 2 fixation rates were positively correlated with the formation of rosette-like cellular structures, and an increased concentration of nitrogenase was observed toward the center of these structures, which increased their occurrence 600 times when cultures reached maximum N 2 fixation rates vs when they had low rates. Interestingly, N 2 fixation was not completely inhibited under oxic conditions and was accompanied by increased formation of capsules and cysts. Rosettes, as well as capsules and cysts, may thus serve as protection against O 2 . Our study reveals the physiological adaptations that underlie N 2 fixation in an anoxygenic phototroph, emphasizing the significance of biofilm formation for utilizing light and fixing N 2 under oxic conditions, and underscores the need for deciphering the importance of light for marine NCDs. IMPORTANCE The contribution of non-cyanobacterial diazotrophs (NCDs) to total N 2 fixation in the marine water column is unknown, but their importance is likely constrained by the limited availability of dissolved organic matter and low O 2 conditions. Light could support N 2 fixation and growth by NCDs, yet no examples from bacterioplankton exist. In this study, we show that the phototrophic NCD, Rhodopseudomonas sp. BAL398, which is a member of the diazotrophic community in the surface waters of the Baltic Sea, can utilize light. Our study highlights the significance of biofilm formation for utilizing light and fixing N 2 under oxic conditions and the role of cell plasticity in regulating these processes. Our findings have implications for the general understanding of the ecology and importance of NCDs in marine waters.

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Spatial Distribution, Diversity, and Activity of Microbial Phototrophs in the Baltic Sea

Cited by 3 publications

References 93 publications

Direct biological fixation provides a freshwater sink for N2O

Direct biological fixation provides a freshwater sink for N2O

Biodiversity of microorganisms in the Baltic Sea: the power of novel methods in the identification of marine microbes

Biofilm formation and cell plasticity drive diazotrophy in an anoxygenic phototrophic bacterium

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