Abstract
Simple SummaryNitrogen acquisition strategies mediated by insect symbionts through biological nitrogen fixation (BNF) and nitrogenous waste recycling (NWR) were reviewed and compared in our paper, and a model for nitrogen provisioning in insects was then constructed. In our model, (1) insects acquired nitrogen nutrition from food stuffs directly, and the subprime channels (e.g., BNF or NWR) for nitrogen provisioning were accelerated when the available nitrogen in diets could not fully support the normal growth and development of insects; (2) the NWR strategy was more accessible to more insects due to its energy conservation and mild reaction conditions; (3) ammonia produced by different channels was used for essential nitrogenous metabolites synthesis via the glutamine synthetase and glutamate synthase pathways.Nitrogen is usually a restrictive nutrient that affects the growth and development of insects, especially of those living in low nitrogen nutrient niches. In response to the low nitrogen stress, insects have gradually developed symbiont-based stress response strategies—biological nitrogen fixation and nitrogenous waste recycling—to optimize dietary nitrogen intake. Based on the above two patterns, atmospheric nitrogen or nitrogenous waste (e.g., uric acid, urea) is converted into ammonia, which in turn is incorporated into the organism via the glutamine synthetase and glutamate synthase pathways. This review summarized the reaction mechanisms, conventional research methods and the various applications of biological nitrogen fixation and nitrogenous waste recycling strategies. Further, we compared the bio-reaction characteristics and conditions of two strategies, then proposed a model for nitrogen provisioning based on different strategies.
Highlights
Nitrogen is an essential nutrient for insects, largely required for building cells, tissues, and life molecules [1]
Three alternative scenarios of symbiotic NWR, different in their patterns of amino acid synthesis using waste ammonia, may be functional in the symbiosis between insects and symbionts [15]: (A) Symbiont-mediated: Symbionts convert nitrogenous waste compounds of insects into EAAs for host assimilation and absorption; (B) Mediated by host cell– symbiont complex: Ammonia is firstly assimilated into non-essential amino acids by GS/GOGAT in insect cells. nEAAs are used as ammonia donors to synthesize EAAs in symbionts; (C) Host cell-mediated: Ammonia is assimilated into glutamate by GS/GOGAT in insect cells
The genome of endosymbiont Dactylopiibacterium mainly located in the ovaries of the carmine cochineal insects (D. coccus, D. opuntiae) was sequenced, and the data showed that purine and uric acid degrading genes were present in its genome [56]
Summary
Nitrogen is an essential nutrient for insects, largely required for building cells, tissues, and life molecules [1]. Nitrogen acquisition strategies mediated by insect symbionts mainly include nitrogen enrichment, biological nitrogen fixation (BNF) and nitrogenous waste recycling. We systematically summarized the reaction mechanisms, conventional research methods and application cases of these two strategies in insects, aiming to better understand the highly efficient nitrogen economy existing in insect–symbiont complexes. The classical BNF reaction is catalyzed by nitrogenase complex (Mo/Fe nitrogenase), which consists of two main functional subunits: dinitrogenase reductase (γ2 homodimeric azoferredoxin, encoded by nifH gene) and dinitrogenase (α2β2 heterotetrameric molybdoferredoxin, encoded by nifD and nifK genes). The reduction of atmospheric nitrogen to ammonia is catalyzed only if they form a complex with each other In this reaction, the [4Fe-4S] cluster on dinitrogenase reductase accepts electrons provided by electron donors (such as ferredoxin and flavodoxin) and transfers electrons to the metal atom center (P clusters) on dinitrogenase. Fe/V nitrogenase has only been reported in Azotobacter vinelandii and A. chroococcum, while Fe/Fe nitrogenase has only been demonstrated in A. vinelandii and Rhodobacter capsulatus [12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
