Biology subjects

Plummer, S.

Publications and source records attributed to Plummer, S..

3 recordsLinked to original sources

bioRxiv2025

Enzymatically active exudates from Alteromonas facilitate Prochlorococcus survival in stationary phase

The cyanobacterium Prochlorococcus has a conspicuously reduced genome causing it to require help from co-existing organisms for survival under a variety of stressful conditions. In this work we demonstrated that the heterotrophic bacterium Alteromonas macleodii EZ55 facilitated the survival of Prochlorococcus MIT9312 batch co-cultures as they entered stationary phase. We further showed that exudates from both Alteromonas and Prochlorococcus were responsible for this effect. Unidentified toxic exudates of Prochlorococcus lowered the carrying capacity of Pro99 medium for axenic Prochlorococcus cells, whereas heat-labile high-molecular weight exudates of Alteromonas both removed the effect of Prochlorococcus exudates and extended the lifespan of axenic Prochlorococcus cultures. Alteromonas exudates contained a wide variety of proteins and demonstrated enzymatic activities. Some of these proteins and activities may have been packaged within extracellular membrane vesicles, which we identified within Alteromonas exudates and found capable of physically associating with Prochlorococcus cells. Many of the functionalities observed in Alteromonas exudates (e.g., increasing phosphate availability, degrading hydrogen peroxide) were consistent with leaky Black Queen processes, which are defined as services provided by one organism that benefit the entire community and favor the evolution of interdependencies in microbial communities. Therefore, we discuss the potential ramifications of such processes being packaged into vesicles as opposed to freely diffusing through the extracellular milieu.

microbiology↗

bioRxiv2025

Extracellular superoxide production is a widespread photoacclimation strategy in phytoplankton

Phytoplankton control the habitability of Earth. These photosynthetic microorganisms serve as the base of marine food webs, produce approximately half of the planets oxygen, and regulate climate by sequestering carbon dioxide from the atmosphere. As global changes accelerate through the Anthropocene, phytoplankton communities face multiple stressors, including warming, shifting patterns in ocean circulation and structure, and associated perturbations in levels of light exposure. The health and functioning of the oceans depends on phytoplankton community responses to these stressors; however, the physiological processes involved in light stress are not fully understood. Here, we surveyed sixteen representative phytoplankton and show that most produce extracellular superoxide, an otherwise damaging reactive oxygen species, as a widespread strategy to acclimate to light stress. Indeed, all species regulated extracellular superoxide production as a function of light exposure, which was modeled with a modified photosynthesis-irradiance (PE) curve. Furthermore, the flavoenzyme inhibitor DPI quenched extracellular superoxide production and lead to declines in viability and photosynthetic health in thirteen out of sixteen species. The negative effect of DPI on photosynthetic health was stronger with increasing light, consistent with inhibition of a photoprotective process. Taken together, these results support the hypothesis that phytoplankton mitigate light stress through enzyme-mediated production of extracellular superoxide. These results imply that daytime rates of biological superoxide production in the marine environment are substantially underestimated by dark measurements. Furthermore, phytoplankton photoacclimation may alter superoxide production rates in future oceans impacted by changes in water column structure and light exposure.

microbiology↗

bioRxiv2023

Energy flux couples sulfur isotope fractionation to proteomic and metabolite profiles in Desulfovibrio vulgaris

Microbial sulfate reduction is central to the global carbon cycle and the redox evolution of Earths surface. Tracking the activity of sulfate reducing microorganisms over space and time relies on a nuanced understanding of stable sulfur isotope fractionation in the context of the biochemical machinery of the metabolism. Here we link the magnitude of stable sulfur isotopic fractionation to proteomic and metabolite profiles under different cellular energetic regimes. When energy availability is limited, cell specific sulfate respiration rates and net sulfur isotope fractionation inversely co-vary. Beyond net S isotope fractionation values, we also quantified shifts in protein expression, abundances and isotopic composition of intracellular S metabolites, and lipid structures and lipid/water H isotope fractionation values. These coupled approaches reveal which protein abundances shift directly as a function of energy flux, those that vary minimally, and those that may vary independent of energy flux and likely do not contribute to shifts in S-isotope fractionation. By coupling the bulk S-isotope observations with quantitative proteomics, we provide novel constraints for metabolic isotope models. Together, these results lay the foundation for more predictive metabolic fractionation models, alongside interpretations of environmental sulfur and sulfate reducer lipid-H isotope data.

microbiology↗