Rapid mode switching facilitates the growth ofTrichodesmium: A model analysis

Abstract

AbstractTrichodesmiumis one of the dominant dinitrogen(N2)-fixers in the ocean, influencing global carbon and nitrogen cycles through its biochemical reactions. Although the photosynthetic activity ofTrichodesmiumfluctuates rapidly at the cellular level, the physiological or ecological advantage of this characteristic is not clear. Here we develop a metabolic model ofTrichodesmiumthat 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 N2fixation in photosynthetic states. Our results show that a rapid switch between photosynthetic and non-photosynthetic states increasesTrichodesmiumgrowth 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 allTrichodesmiumcells 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 N2fixation that allowsTrichodesmiumto fix N2aerobically in the global ocean.