Biology subjects

Prasil, O.

Publications and source records attributed to Prasil, O..

3 recordsLinked to original sources

bioRxiv2025

Modeling dynamic oxygen permeability as a mechanism to mitigate oxygen-induced stresses on photosynthesis and N2 fixation in marine Trichodesmium

Trichodesmium, the predominant marine diazotrophic cyanobacterium, concurrently performs nitrogen (N2) fixation and photosynthesis, the latter of which produces oxygen (O2) that inhibits N2 fixation. Hopanoid lipids in Trichodesmium may play a role in dynamically regulating membrane permeability to O2, potentially alleviating O2 stress on N2 fixation. However, the physiological impacts of this dynamic permeability are not well understood. We developed a model showing that dynamically modulating membrane O2 permeability can enhance N2 fixation and growth of Trichodesmium by over 50%. High O2 permeability (1.5x10-4 of O2 diffusivity in seawater) during strong photosynthesis accelerates O2 exhaust, reducing energy-consuming photorespiration by [~]40%, while low O2 permeability (1.0x10-5 diffusivity) during active N2 fixation minimizes O2 stress on N2 fixation. Together, these mechanisms increase the carbon and iron use efficiencies by [~]70%. Our study provides a mechanistic and quantitative framework for how dynamic O2 permeability benefits Trichodesmium, offering insights potentially applicable to other diazotrophs. IMPORTANCETrichodesmium is a key player in marine N2 fixation, essential for oceanic productivity and global biogeochemical cycles. However, a significant challenge arises from the concurrent photosynthetic production of O2 during N2 fixation, which can inhibit N2 fixation and cause energy-wasting photorespiration. We develop a physiological model showing that Trichodesmium may dynamically regulate membrane O2 permeability to enhance N2 fixation and growth. The model suggests two mechanisms: elevated O2 permeability during the early daytime of strong photosynthesis accelerates O2 exhaust to environment, reducing photorespiration, while reduced O2 permeability later limits O2 influx from environment, lowering wasteful respiration and maintaining a low intracellular O2 level for active N2 fixation. These adaptations improve the efficiency of carbon and iron utilization, thereby facilitating N2 fixation and growth in Trichodesmium. This study sheds light on how Trichodesmium and other N2-fixing microorganisms can optimize their physiological processes in response to environmental challenges. HIGHLIGHTSO_LIWe developed a metabolic flux model of Trichodesmium, which resolves Dynamic cellular Permeability to O2 (DPO2). C_LIO_LIDPO2 increases N2 fixation and growth rates. C_LIO_LIDPO2 increases growth efficiency by reducing carbon wasting processes such as photorespiration and respiratory protection. C_LIO_LIDPO2, as a result, also increases iron utilization efficiency. C_LI

microbiology↗

bioRxiv2023

Photo-physiological Acclimation in Synechocystis sp. PCC 6803 Provides Insight into Growth Limitation in Underwater Spectra

Cyanobacteria play a key role in primary production in both oceans and fresh waters and hold great potential for sustainable production of a large number of commodities. During their life, cyanobacteria cells need to acclimate to a multitude of challenges, including shifts in intensity and quality of incident light. Despite our increasing understanding of metabolic regulation under various light regimes, detailed insight into fitness advantages and limitations under shifting light quality has been missing. Here, we study photo-physiological acclimation in the cyanobacterium Synechocystis sp. PCC 6803 through the whole range of photosynthetically active radiation (PAR). Using LEDs with qualitatively different narrow spectra, we describe wavelength dependence of light capture, electron transport and energy transduction to main cellular pools. In addition, we describe processes fine-tuning light capture such as state transitions and efficiency of energy transfer from phycobilisomes to photosystems. We show that growth was the most limited under blue light due to inefficient light harvesting, and that many cellular processes are tightly linked to the redox state of the PQ pool, which was the most reduced under red light. The PSI-to-PSII ratio was low under blue photons, however, it was not the main growth-limiting factor, since it was even more reduced under violet and near far-red lights, where Synechocystis grew faster compared to blue light. Our results provide insight into the spectral dependence of phototrophic growth and can provide the foundation for future studies of molecular mechanisms underlying light acclimation in cyanobacteria, leading to light optimization in controlled cultivations.

plant biology↗

bioRxiv2021

Crocosphaera as a major consumer of fixed nitrogen despite its capability of nitrogen fixation

Crocosphaera watsonii (hereafter Crocosphaera) is a key nitrogen (N) fixer in the ocean, but its ability to consume combined N sources is still unclear. Using in situ microcosm incubations with an ecological model, we show that Crocosphaera has high competitive capability both under low and moderately high combined N concentrations. In field incubations, Crocosphaera accounted for the highest consumption of ammonium and nitrate, followed by pico-eukaryotes. The model analysis shows that cells have a high ammonium uptake rate ([~]7 mol N (mol N)-1 d-1 at the maximum), which allows them to compete against pico-eukaryotes and non-diazotrophic cyanobacteria when combined N is sufficiently available. Even when combined N is depleted, their capability of nitrogen fixation allows higher growth rates compared to potential competitors. These results suggest the high fitness of Crocosphaera in combined N limiting, oligotrophic oceans, and thus heightens its potential significance in its ecosystem and in biogeochemical cycling.

microbiology↗