Profiles

Marcus Stenegren

Marcus Stenegren

Doktorand

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Works at Department of Ecology, Environment and Plant Sciences
Telephone 08-16 38 46
Email marcus.stenegren@su.se
Visiting address Svante Arrhenius väg 20 A
Room N 495
Postal address Institutionen för ekologi miljö och botanik 106 91 Stockholm

About me

PhD candidate in the R.A. Foster lab at the Department of Ecology, Environment and Plant Sciences (DEEP).

My educational background is a Bachelor (2011) and Masters (2013) Degree in Marine and Environmental Science, respectively, both at the University of Gothenburg.

I have a long standing passion for our oceans, which started when I, as a teenager, experienced scuba diving for the first time.

I'm particularly interested in how the differing marine environments govern their inhabitants and how, in turn, these inhabitants are able to either modify or cope with it. For example microorganisms that play vital roles in marine biogeochemical cycles, subsequently affecting biological systems on a global scale.

 

Teaching

I'm a certified team-building instructor (UGL) and have organized workshops and taught at PhD level on communication, feedback and presentation technique.

 

Research

I'm studying the complex symbiosis between cyanobacterial nitrogen fixers, also called diazotrophs, and their phytoplankton hosts in tropical open ocean ecosystems. The ability to fix atmospheric nitrogen into a bioavailable nutrient is unique and is only present in a small group of bacteria and archaea. Thanks to their nitrogen fixation cyanobacteria fertilize the phytoplankton community in oligotrophic oceans and promotes colonization of oceanic regions which otherwise would have been uninhabitable for many phytoplankton. The phytoplankton, e.g. diatoms, photosynthesise, fixing atmospheric carbon and release the biproduct oxygen which we need for breathing. Moreover, when the phytoplankton die, a small, but important, fraction of the fixed carbon will sequester down to the ocean floor where it stays for a long period of time.

Initially, I'm doing this research using traditional molecular methods, like quantitative Polymerase Chain Reaction (qPCR) and gene specific microarrays, putting these associations into an ecological context. I'm also interested in seeing how and why they show certain patterns of distribution and activity in relation to biotic and abiotic environmental factors.

The generated data is used as input into novel ecological models, like the piecewise Structural Equation Model (SEM), to try and disentangle relevant ecological questions and formulating new testable hypotheses.

 

The Research Group

Rachel Foster (Supervisor)

Mercedes Nieves Morión (Postdoc)

Andrea Caputo (PhD candidate)

 

Publications

Stenegren, M., Berg, C., Padilla, C.C., David, S-S., Montoya, J.P., Yager, P.L. and Foster R.A. (2017) Piecewise Structural Equation Model (SEM) Disentangles the Environmental Conditions Favoring Diatom Diazotroph Associations (DDAs) in the Western Tropical North Atlantic (WTNA). Front. Microbiol. 8:810. doi: 10.3389/fmicb.2017.00810.

Stenegren, M., Caputo, A., Berg, C., Bonnet, S. and Foster, R.A. Distribution and drivers of symbiotic and free-living diazotrophic cyanobacteria in the Western Tropical South Pacific. Biogeosciences Discuss., doi:10.5194/bg-2017-63, accepted, 2017.

Caputo, C., Stenegren, M., Pernice, M.C. and Foster, R.A. (2018) Short comparison of Two Marine Planktonic Diazotrophic Symbioses Highlights an Un-quantified Disparity. Front. Microbiol. 5.2. doi=10.3389/fmars.2018.00002.

Publications

A selection from Stockholm University publication database
  • 2017. Marcus Stenegren, Rachel Foster, Bethany Jenkins.

    Di-nitrogen (N2) fixation plays a crucial role in oceanic carbon and nitrogen cycles and is important for marine biogeochemistry on regional and global scales. N2-fixing (diazotrophs) cyanobacteria are considered to contribute the most to marine nitrogen fixation, and thereby fuel the surrounding phytoplankton communities with bioavailable ammonia. Distribution and activity of phytoplankton, including diazotrophs, are largely driven by environmental conditions and temperature is often considered the main influence. A greater understanding of the environmental conditions that govern the diazotrophs, is vital to accurate predictions and estimations for the marine nitrogen budget, as well as understanding their impact on the nitrogen and carbon cycles.

    Therefore, the primary aim of this thesis was to determine abundances and distribution patterns for various cyanobacterial diazotrophs in two different regions that in spite of their hydrological differences are prime regions for diazotrophy. Moreover, we attempted to identify the environmental conditions that govern cyanobacterial diazotrophs abundance.

    In the first study we observed a clear separation of the unicellular diazotroph UCYN-A from the other diazotrophs, including the other unicellular types (UCYN-B, UCYN-C) in the Western Tropical South Pacific. The main driver of the vertical distribution of diazotrophs was based on a temperature-depth gradient, which was similar to the findings of our meta-analysis which included 11 additional datasets. Using newly and previously designed primers and probe sets for the UCYN-A1 and A2 hosts, we also observed discrepancies in detection and abundance for the two UCYN-A symbiotic strains (A1 and A2) and their respective hosts, which is in contrast to the current understanding of a highly specific and obligate partnership. Lastly, cross-hybridization tests revealed that the qPCR assay targeting the UCYN-A2 strain also enumerated UCYN-A1, demonstrating the difficulty in quantifying closely related strains.

    In the second study we distinguished the environmental conditions favoring two closely related heterocystous cyanobacterial strains of Richelia intracellularis (het-1 and het-2) which associate with two different diatom hosts (Rhizosolenia and Hemiaulus, respectively) in the Western Tropical North Atlantic (WTNA). In general, the Amazon River (AR) plume heavily influenced het-1 and het-2 abundances; higher densities were quantified at stations with mesohaline sea surface salinities and maximum abundances were detected in the sub-surface, below the freshwater discharge. However, maximum abundances at oceanic sea surface salinity stations were observed nearer to the surface. A piecewise Structural Equation Model (SEM) was developed and identified turbidity as an important factor governing het-1 and het-2 abundance. In addition, het-1 and het-2 distribution pattern was influenced by dissolved inorganic phosphorus (DIP) concentration and salinity. Het-1 tended to penetrate deeper waters and was favored by increased salinity, while the opposite was true for het-2.

    The results of this thesis contribute to a better understanding of marine cyanobacterial diazotrophs’ ecological niches and will prove useful in future predictions and research on nitrogen fixation, and the role of cyanobacterial diazotrophs in marine biogeochemistry.

Show all publications by Marcus Stenegren at Stockholm University

Last updated: October 4, 2018

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