Biology subjects

Armin, G.

Publications and source records attributed to Armin, G..

3 recordsLinked to original sources

bioRxiv2023

Rapid mode switching facilitates the growth of Trichodesmium: A model analysis.

Trichodesmium is one of the dominant dinitrogen(N2)-fixers in the ocean, influencing global carbon and nitrogen cycles through its biochemical reactions. Although the photosynthetic activity of Trichodesmium fluctuates rapidly at the cellular level, the physiological or ecological advantage of this characteristic is not clear. Here we develop a metabolic model of Trichodesmium that can perform dinitrogen (N2) fixation during the daytime. We examined (1) the effect of the duration of switches between photosynthetic and non-photosynthetic cellular states and (2) the effect of the presence and absence of N2 fixation in photosynthetic states. Our results show that a rapid switch between photosynthetic and non-photosynthetic states increases Trichodesmium growth rates by improving metabolic efficiencies due to optimized C and N metabolism. Our results show the possibility and advantage of the rapid switch, providing a strategy for previous observations that all Trichodesmium cells can contain nitrogenase, which was previously considered to be a paradox. This study reveals the importance of fluctuating photosynthetic activity and provides a mechanism for daytime N2 fixation that allows Trichodesmium to fix N2 aerobically in the global ocean.

ecology↗

bioRxiv2022

Proton-pumping rhodopsins in marine diatoms

Diatoms are a major phytoplankton group responsible for about 20% of Earths primary production. They carry out photosynthesis inside the plastid, an organelle obtained through eukaryote-eukaryote endosymbiosis. Recently, microbial rhodopsin, a photoreceptor distinct from chlorophyll-based photosystems, has been identified in certain diatoms. However, the physiological function of diatom rhodopsin is not well understood. Here we show that the diatom rhodopsin acts as a light-driven proton pump and localizes to the outermost membrane of the four membrane-bound complex plastids. Heterologous expression techniques were used to investigate the protein function and subcellular localization of diatom rhodopsin. Using model simulations, we further evaluated the physiological role of the acidic pool in the plastid produced by proton-transporting rhodopsin. Our results propose that the rhodopsin-derived acidic pool may be involved in a photosynthetic CO2-concentrating mechanism and assist CO2 fixation in diatom cells.

microbiology↗

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↗