ORCID Profile
0000-0002-1966-5315
Current Organisation
University of North Carolina at Chapel Hill
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Publisher: Springer Science and Business Media LLC
Date: 03-10-2022
DOI: 10.1038/S43705-022-00181-W
Abstract: Southern Ocean (SO) diatoms play an important role in global carbon flux, and their influence on carbon export is directly linked to interactions with epiphytic bacteria. Bacterial symbionts that increase diatom growth promote atmospheric carbon uptake, while bacterial degraders ert diatom biomass into the microbial loop where it can then be released as carbon dioxide through respiration. To further explore SO diatom-bacterial associations, a natural model system is needed that is representative of these erse and important interactions. Here, we use concurrent cultivation to isolate a species of the ecologically-important SO diatom, Pseudo-nitzschia subcurvata , and its co-occurring bacteria. Although vitamin-depleted, axenic Pseudo-nitzschia grew poorly in culture, addition of a co-isolated Roseobacter promoted diatom growth, while addition of a co-isolated Flavobacterium negatively impacted diatom growth. Microscopy revealed both bacterial isolates are physically associated with diatom cells and genome sequencing identified important predicted functions including vitamin synthesis, motility, cell attachment mechanisms, and erse antimicrobial weapons that could be used for interbacterial competition. These findings revealed the natural coexistence of competing symbiotic strategies of diatom-associated bacteria in the SO, and the utility of this tripartite system, composed of a diatom and two bacterial strains, as a co-culture model to probe ecological-relevant interactions between diatoms and the bacteria that compete for access to the phycosphere.
Publisher: Wiley
Date: 10-11-2022
DOI: 10.1002/LOL2.10223
Abstract: It has recently been shown that Southern Ocean phytoplankton species have evolved to optimize their light‐harvesting potential without increasing the high iron‐requiring proteins used for photosynthesis. We measured molecular and physiological responses of phytoplankton cultures under a combination of iron and light conditions. While iron‐replete cultures mostly increased biovolume, photochemical efficiency ( F v / F m ) and the relative abundance of photosystem II (PSII) and Cytochrome b 6 f protein compared to iron‐limited cultures, light also regulated cellular chlorophyll a content and played a role in controlling PSII protein abundance. Investment of protein resources into the carbon fixing enzyme Ribulose 1,5‐bisphosphate carboxylase oxygenase (Rubisco) was species‐specific, but increased growth rates correlated with increased investment into Rubisco for all species. Our results suggest that Proboscia inermis uses a ergent molecular strategy to compete for nutrients, light, and CO 2 in the Southern Ocean.
Publisher: Inter-Research Science Center
Date: 20-01-2022
DOI: 10.3354/MEPS13923
Abstract: Model projections for the Southern Ocean indicate that light, iron (Fe) availability, temperature and carbon dioxide (CO 2 ) will change concurrently in the future. We investigated the physiological responses of Southern Ocean phytoplankton to multiple variables by culturing the haptophyte Phaeocystis antarctica and the diatom Chaetoceros flexuosus under various combinations of light, Fe, temperature and CO 2 . Using statistical models, the influence of each environmental variable was analysed for each physiological response, ultimately predicting how ‘future’ conditions (high temperature and high CO 2 ) would influence the 2 phytoplankton species. Under future conditions, cellular chlorophyll a and carbon to nitrogen molar ratios were modelled to increase for both species in all light and Fe treatments, but at times were inconsistent with measured values. Measured and modelled values of the photochemical efficiency of photosystem II ( F v / F m ) declined in cultures of P. antarctica due to concurrent increases in temperature and CO 2 , under all light and Fe treatments. The trends in F v / F m for C. flexuosus were less clear. Our model and observations suggest that when temperature and CO 2 are concurrently increased, the growth of both species remains largely unchanged. This modelling analysis reveals that high CO 2 exerts a strong negative influence on the growth of both phytoplankton, and any ‘future’ increase in growth can be attributed to the positive effect of warming rather than a CO 2 fertilisation effect.
Publisher: Frontiers Media SA
Date: 11-2019
Location: United States of America
No related grants have been discovered for Sarah Andrew.