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Microorganisms
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Phytoplankton-Bacteria Interactions 2.0
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Phytoplankton-Bacteria Interactions 2.0

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Environmental Microbiology".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 16041

Special Issue Editor

Dr. Katherina Petrou

E-Mail Website1 Website2
Guest Editor
School of Life Sciences, University of Technology Sydney, Sydney, Australia
Interests: marine microalgal phenotypic plasticity; ecophysiology; photobiology; cell biochemistry; ocean biogeochemical cycling; phytoplankton–bacteria interactions; coral physiology and symbiosis; single-cell methodologies; cell–cell interface dynamics; ecophysiological responses to climate change; adaptation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue is the continuation of our 2021 Special Issue “Phytoplankton–Bacteria Interactions”.

Whether obligate, facultative, mutualistic, or parasitic, phytoplankton–bacteria relationships play an important role in aquatic ecosystems. These ubiquitous inter-domain interactions are often mediated directly by cell-to-cell attachment but can also occur indirectly via the release of chemicals into the surrounding water. Together, phytoplankton and bacteria are principal players in modulating biogeochemistry and nutrient cycling and, by way of their effect on each other’s physiology and metabolism, often define ecosystem productivity. Therefore, examining cell-scale processes that govern phytoplankton–bacteria networks and associations is important if we are to form a deeper understanding of the underpinnings of our major ecosystems.

This Special Issue focused on the importance of phytoplankton–bacteria relationships in aquatic environments will provide in-depth coverage, including new ideas and scientific advances into understanding the intricacies of such interactions. I kindly invite authors to submit a review article, an original research article, or a short communication on topics related to (1) the evolutionary development of phytoplankton–bacteria associations, (2) the physiological and metabolic responses controlling their interactions, (3) phytoplankton–bacterial modulation of biogeochemistry or nutrient cycling, (4) the ecological or physiological role of bacteria in harmful algae, and (5) the chemistry or chemical signaling of phytoplankton–bacteria associations. Method studies or perspectives on new methodologies and techniques for probing these relationships are also welcome.

As Guest Editor of this Special Issue, I look forward to reviewing your interesting submissions.

Dr. Katherina Petrou
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Microorganisms is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • environmental microbiology
  • microbe interactions
  • phytoplankton ecology
  • biogeochemical cycling
  • microbiome
  • pathogenicity
  • symbioses
  • chemotaxis

Published Papers (7 papers)

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Editorial

Jump to: Research, Review

3 pages, 177 KiB  
Editorial
Phytoplankton-Bacteria Interactions 2.0
by Katherina Petrou
Microorganisms 2023, 11(6), 1536; https://doi.org/10.3390/microorganisms11061536 - 09 Jun 2023
Viewed by 796
Abstract
There are multiple ways in which phytoplankton and bacteria interact, starting from the fundamental symbiotic associations of direct attachment, through intimate interactions within the phytoplankton phycosphere, to random associations within the water column via the exudation and cycling of dissolved organic carbon (DOC) [...] Read more.
There are multiple ways in which phytoplankton and bacteria interact, starting from the fundamental symbiotic associations of direct attachment, through intimate interactions within the phytoplankton phycosphere, to random associations within the water column via the exudation and cycling of dissolved organic carbon (DOC) and other chemical compounds [...] Full article
(This article belongs to the Special Issue Phytoplankton-Bacteria Interactions 2.0)

Research

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15 pages, 2585 KiB  
Article
Effects of Phycosphere Bacteria on Their Algal Host Are Host Species-Specific and Not Phylogenetically Conserved
by Dylan Baker, James Lauer, Anna Ortega, Sara L. Jackrel and Vincent J. Denef
Microorganisms 2023, 11(1), 62; https://doi.org/10.3390/microorganisms11010062 - 25 Dec 2022
Cited by 2 | Viewed by 2722
Abstract
Phytoplankton is fundamental to life on Earth. Their productivity is influenced by the microbial communities residing in the phycosphere surrounding algal cells. Expanding our knowledge on how algal-bacterial interactions affect algal growth to more hosts and bacteria can help elucidate general principles of [...] Read more.
Phytoplankton is fundamental to life on Earth. Their productivity is influenced by the microbial communities residing in the phycosphere surrounding algal cells. Expanding our knowledge on how algal-bacterial interactions affect algal growth to more hosts and bacteria can help elucidate general principles of algal-host interactions. Here, we isolated 368 bacterial strains from phycosphere communities, right after phycosphere recruitment from pond water and after a month of lab cultivation and examined their impacts on growth of five green algal species. We isolated both abundant and rare phycosphere members, representing 18.4% of the source communities. Positive and neutral effects predominated over negative effects on host growth. The proportion of each effect type and whether the day of isolation mattered varied by host species. Bacteria affected algal carrying capacity more than growth rate, suggesting that nutrient remineralization and toxic byproduct metabolism may be a dominant mechanism. Across-host algal fitness assays indicated host-specific growth effects of our isolates. We observed no phylogenetic conservation of the effect on host growth among bacterial isolates. Even isolates with the same ASV had divergent effects on host growth. Our results emphasize highly specific host-bacterial interactions in the phycosphere and raise questions as to which mechanisms mediate these interactions. Full article
(This article belongs to the Special Issue Phytoplankton-Bacteria Interactions 2.0)
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20 pages, 2403 KiB  
Article
Phytoplankton Responses to Bacterially Regenerated Iron in a Southern Ocean Eddy
by Marion Fourquez, Robert F. Strzepek, Michael J. Ellwood, Christel Hassler, Damien Cabanes, Sam Eggins, Imojen Pearce, Stacy Deppeler, Thomas W. Trull, Philip W. Boyd and Matthieu Bressac
Microorganisms 2022, 10(8), 1655; https://doi.org/10.3390/microorganisms10081655 - 16 Aug 2022
Cited by 4 | Viewed by 2541
Abstract
In the Subantarctic sector of the Southern Ocean, vertical entrainment of iron (Fe) triggers the seasonal productivity cycle but diminishing physical supply during the spring to summer transition forces microbial assemblages to rapidly acclimate. Here, we tested how phytoplankton and bacteria within an [...] Read more.
In the Subantarctic sector of the Southern Ocean, vertical entrainment of iron (Fe) triggers the seasonal productivity cycle but diminishing physical supply during the spring to summer transition forces microbial assemblages to rapidly acclimate. Here, we tested how phytoplankton and bacteria within an isolated eddy respond to different dissolved Fe (DFe)/ligand inputs. We used three treatments: one that mimicked the entrainment of new DFe (Fe-NEW), another in which DFe was supplied from bacterial regeneration of particles (Fe-REG), and a control with no addition of DFe (Fe-NO). After 6 days, 3.5 (Fe-NO, Fe-NEW) to 5-fold (Fe-REG) increases in Chlorophyll a were observed. These responses of the phytoplankton community were best explained by the differences between the treatments in the amount of DFe recycled during the incubation (Fe-REG, 15% recycled c.f. 40% Fe-NEW, 60% Fe-NO). This additional recycling was more likely mediated by bacteria. By day 6, bacterial production was comparable between Fe-NO and Fe-NEW but was approximately two-fold higher in Fe-REG. A preferential response of phytoplankton (haptophyte-dominated) relative to high nucleic acid (HNA) bacteria was also found in the Fe-REG treatment while the relative proportion of diatoms increased faster in the Fe-NEW and Fe-NO treatments. Comparisons between light and dark incubations further confirmed the competition between picophytoplankton and HNA for DFe. Overall, our results demonstrate great versatility by microorganisms to use different Fe sources that results in highly efficient Fe recycling within surface waters. This study also encourages future research to further investigate the interactions between functional groups of microbes (e.g. HNA and cyanobacteria) to better constraint modeling in Fe and carbon biogeochemical cycles. Full article
(This article belongs to the Special Issue Phytoplankton-Bacteria Interactions 2.0)
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15 pages, 3578 KiB  
Article
Phytoplankton Sources and Sinks of Dimethylsulphoniopropionate (DMSP) in Temperate Coastal Waters of Australia
by Eva Fernandez, Justin R. Seymour and Katherina Petrou
Microorganisms 2022, 10(8), 1539; https://doi.org/10.3390/microorganisms10081539 - 29 Jul 2022
Cited by 2 | Viewed by 1388
Abstract
The ecologically important organic sulfur compound, dimethylsulfoniopropionate (DMSP), is ubiquitous in marine environments. Produced by some species of phytoplankton and bacteria, it plays a key role in cellular responses to environmental change. Recently, uptake of DMSP by non-DMSP-producing phytoplankton species has been demonstrated, [...] Read more.
The ecologically important organic sulfur compound, dimethylsulfoniopropionate (DMSP), is ubiquitous in marine environments. Produced by some species of phytoplankton and bacteria, it plays a key role in cellular responses to environmental change. Recently, uptake of DMSP by non-DMSP-producing phytoplankton species has been demonstrated, highlighting knowledge gaps concerning DMSP distribution through the marine microbial food web. In this study, we traced the uptake and distribution of DMSP through a natural marine microbial community collected from off the eastern coastline Australia. We found a diverse phytoplankton community representing six major taxonomic groups and conducted DMSP-enrichment experiments both on the whole community, and the community separated into large (≥8.0 µm), medium (3.0–8.0 µm), and small (0.2–3.0 µm) size fractions. Our results revealed active uptake of DMSP in all three size fractions of the community, with the largest fraction (>8 µm) forming the major DMSP sink, where enrichment resulted in an increase of DMSPp by 144%. We observed evidence for DMSP catabolism in all size fractions with DMSP enrichment, highlighting loss from the system via MeSH or DMS production. Based on taxonomic diversity, we postulate the sources of DMSP were the dinoflagellates, Phaeocystis sp., and Trichodesmium sp., which were present in a relatively high abundance, and the sinks for DMSP were the diatoms and picoeucaryotes in this temperate community. These findings corroborate the role of hitherto disregarded phytoplankton taxa as potentially important players in the cycling of DMSP in coastal waters of Australia and emphasize the need to better understand the fate of accumulated DMSP and its significance in cellular metabolism of non-DMSP producers. Full article
(This article belongs to the Special Issue Phytoplankton-Bacteria Interactions 2.0)
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18 pages, 1716 KiB  
Article
Sharing Vitamin B12 between Bacteria and Microalgae Does Not Systematically Occur: Case Study of the Haptophyte Tisochrysis lutea
by Charlotte Nef, Simon Dittami, Raymond Kaas, Enora Briand, Cyril Noël, Francis Mairet and Matthieu Garnier
Microorganisms 2022, 10(7), 1337; https://doi.org/10.3390/microorganisms10071337 - 01 Jul 2022
Cited by 5 | Viewed by 2792
Abstract
Haptophyte microalgae are key contributors to microbial communities in many environments. It has been proposed recently that members of this group would be virtually all dependent on vitamin B12 (cobalamin), an enzymatic cofactor produced only by some bacteria and archaea. Here, we [...] Read more.
Haptophyte microalgae are key contributors to microbial communities in many environments. It has been proposed recently that members of this group would be virtually all dependent on vitamin B12 (cobalamin), an enzymatic cofactor produced only by some bacteria and archaea. Here, we examined the processes of vitamin B12 acquisition by haptophytes. We tested whether co-cultivating the model species Tisochrysis lutea with B12-producing bacteria in vitamin-deprived conditions would allow the microalga to overcome B12 deprivation. While T. lutea can grow by scavenging vitamin B12 from bacterial extracts, co-culture experiments showed that the algae did not receive B12 from its associated bacteria, despite bacteria/algae ratios supposedly being sufficient to allow enough vitamin production. Since other studies reported mutualistic algae–bacteria interactions for cobalamin, these results question the specificity of such associations. Finally, cultivating T. lutea with a complex bacterial consortium in the absence of the vitamin partially rescued its growth, highlighting the importance of microbial interactions and diversity. This work suggests that direct sharing of vitamin B12 is specific to each species pair and that algae in complex natural communities can acquire it indirectly by other mechanisms (e.g., after bacterial lysis). Full article
(This article belongs to the Special Issue Phytoplankton-Bacteria Interactions 2.0)
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19 pages, 3275 KiB  
Article
Diffusional Interactions among Marine Phytoplankton and Bacterioplankton: Modelling H2O2 as a Case Study
by Naaman M. Omar, Ondřej Prášil, J. Scott P. McCain and Douglas A. Campbell
Microorganisms 2022, 10(4), 821; https://doi.org/10.3390/microorganisms10040821 - 15 Apr 2022
Cited by 4 | Viewed by 2037
Abstract
Marine phytoplankton vary widely in size across taxa, and in cell suspension densities across habitats and growth states. Cell suspension density and total biovolume determine the bulk influence of a phytoplankton community upon its environment. Cell suspension density also determines the intercellular spacings [...] Read more.
Marine phytoplankton vary widely in size across taxa, and in cell suspension densities across habitats and growth states. Cell suspension density and total biovolume determine the bulk influence of a phytoplankton community upon its environment. Cell suspension density also determines the intercellular spacings separating phytoplankton cells from each other, or from co-occurring bacterioplankton. Intercellular spacing then determines the mean diffusion paths for exchanges of solutes among co-occurring cells. Marine phytoplankton and bacterioplankton both produce and scavenge reactive oxygen species (ROS), to maintain intracellular ROS homeostasis to support their cellular processes, while limiting damaging reactions. Among ROS, hydrogen peroxide (H2O2) has relatively low reactivity, long intracellular and extracellular lifetimes, and readily crosses cell membranes. Our objective was to quantify how cells can influence other cells via diffusional interactions, using H2O2 as a case study. To visualize and constrain potentials for cell-to-cell exchanges of H2O2, we simulated the decrease of [H2O2] outwards from representative phytoplankton taxa maintaining internal [H2O2] above representative seawater [H2O2]. [H2O2] gradients outwards from static cell surfaces were dominated by volumetric dilution, with only a negligible influence from decay. The simulated [H2O2] fell to background [H2O2] within ~3.1 µm from a Prochlorococcus cell surface, but extended outwards 90 µm from a diatom cell surface. More rapid decays of other, less stable ROS, would lower these threshold distances. Bacterioplankton lowered simulated local [H2O2] below background only out to 1.2 µm from the surface of a static cell, even though bacterioplankton collectively act to influence seawater ROS. These small diffusional spheres around cells mean that direct cell-to-cell exchange of H2O2 is unlikely in oligotrophic habits with widely spaced, small cells; moderate in eutrophic habits with shorter cell-to-cell spacing; but extensive within phytoplankton colonies. Full article
(This article belongs to the Special Issue Phytoplankton-Bacteria Interactions 2.0)
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Review

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21 pages, 3247 KiB  
Review
Climate Change Impacts on the Marine Cycling of Biogenic Sulfur: A Review
by Rebecca Jackson and Albert Gabric
Microorganisms 2022, 10(8), 1581; https://doi.org/10.3390/microorganisms10081581 - 05 Aug 2022
Cited by 11 | Viewed by 2931
Abstract
A key component of the marine sulfur cycle is the climate-active gas dimethylsulfide (DMS), which is synthesized by a range of organisms from phytoplankton to corals, and accounts for up to 80% of global biogenic sulfur emissions. The DMS cycle starts with the [...] Read more.
A key component of the marine sulfur cycle is the climate-active gas dimethylsulfide (DMS), which is synthesized by a range of organisms from phytoplankton to corals, and accounts for up to 80% of global biogenic sulfur emissions. The DMS cycle starts with the intracellular synthesis of the non-gaseous precursor dimethylsulfoniopropionate (DMSP), which is released to the water column by various food web processes such as zooplankton grazing. This dissolved DMSP pool is rapidly turned over by microbially mediated conversion using two known pathways: demethylation (releasing methanethiol) and cleavage (producing DMS). Some of the formed DMS is ventilated to the atmosphere, where it undergoes rapid oxidation and contributes to the formation of sulfate aerosols, with the potential to affect cloud microphysics, and thus the regional climate. The marine phase cycling of DMS is complex, however, as heterotrophs also contribute to the consumption of the newly formed dissolved DMS. Interestingly, due to microbial consumption and other water column sinks such as photolysis, the amount of DMS that enters the atmosphere is currently thought to be a relatively minor fraction of the total amount cycled through the marine food web—less than 10%. These microbial processes are mediated by water column temperature, but the response of marine microbial assemblages to ocean warming is poorly characterized, although bacterial degradation appears to increase with an increase in temperature. This review will focus on the potential impact of climate change on the key microbially mediated processes in the marine cycling of DMS. It is likely that the impact will vary across different biogeographical regions from polar to tropical. For example, in the rapidly warming polar oceans, microbial communities associated with the DMS cycle will likely change dramatically during the 21st century with the decline in sea ice. At lower latitudes, where corals form an important source of DMS (P), shifts in the microbiome composition have been observed during thermal stress with the potential to alter the DMS cycle. Full article
(This article belongs to the Special Issue Phytoplankton-Bacteria Interactions 2.0)
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