What do we know about biological nitrogen fixation in insects? Evidence and implications for the insect and the ecosystem

Abstract

Many insects feed on a low-nitrogen diet, and the origin of their nitrogen supply is poorly understood. It has been hypothesized that some insects rely on nitrogen-fixing bacteria (diazotrophs) to supplement their diets. Nitrogen fixation by diazotrophs has been extensively studied and convincingly demonstrated in termites, while evidence for the occurrence and role of nitrogen fixation in the diet of other insects is less conclusive. Here, we summarize the methods to detect nitrogen fixation in insects and review the available evidence for its occurrence (focusing on insects other than termites). We distinguish between three aspects of nitrogen fixation investigations: (i) detecting the presence of potential diazotrophs; (ii) detecting the activity of the nitrogen-fixing enzyme; and (iii) detecting the assimilation of fixed nitrogen into the insect tissues. We show that although evidence from investigations of the first aspect reveals ample opportunities for interactions with potential diazotrophs in a variety of insects, demonstrations of actual biological nitrogen fixation and the assimilation of fixed nitrogen are restricted to very few insect groups, including wood-feeding beetles, fruit flies, leafcutter ants, and a wood wasp. We then discuss potential implications for the insect's fitness and for the ecosystem as a whole. We suggest that combining these multiple approaches is crucial for the study of nitrogen fixation in insects, and argue that further demonstrations are desperately needed in order to determine the relative importance of diazotrophs for insect diet and fitness, as well as to evaluate their overall impact on the ecosystem.

Insights Into the Ecological Role of Pseudomonas spp. in an Ant-plant Symbiosis

“…Potential diazotrophic microorganisms have already been recovered from different insect orders, such as Coleoptera, Blattodea, Diptera, Hemiptera and Hymenoptera (Behar et al, 2005;Morales-Jiménez et al, 2009;Pinto-Tomás et al, 2009;Bar-Shmuel et al, 2020). Bacteria belonging to the genus Pantoea, for example, have repeatedly been isolated from the leaf-cutting ants symbiosis sampled in different countries, such as Brazil, Argentina and Panama, and have been able to fix nitrogen in the fungus garden.…”

“…Proteobacteria genera Pantoea, Rhizobium, Methylobacterium, and Pseudomonas have known diazotrophic potential (Borm et al, 2008;Pinto-Tomás et al, 2009;Ruiz-González et al, 2019;Bar-Shmuel et al, 2020). Due to the significant number of strains isolated from Cecropia-Azteca that could potentially fix nitrogen (22; 56.4%), the nitrogenase activity of these strains was tested.…”

The diversity and function of intestinal microorganisms in four geographic Cephalcia chuxiongica (a pine defoliator) populations

“…Plant material is low in nitrogen, specific amino acids, sterols and B vitamins, and in many cases, microorganisms synthesize these components (Dillon & Dillon, 2004). These functions on metabolism processes and nutritional contributions of gut bacteria should be essential in insects living on plants and other suboptimal diets (Bar-Shmuel et al, 2020;Dillon & Dillon, 2004).…”

Diversity and Composition of the Gut Microbiota in the Developmental Stages of the Dung Beetle Copris incertus Say (Coleoptera, Scarabaeidae)

“…These were able to recycle uric acid in vitro, used as a nitrogen source for eggs, larvae, and adults (male and female) of the beetle Dendroctonus valens (Morales-Jiménez et al, 2013). The bacterial nitrogen-fixing activity has been reported in insects like termites, cockroaches, ants, aphids, and beetles [see Bar-Shmuel et al (2020)]; however, none of the contributing genera have been reported as nitrogen fixers in insect gut; with exception of the order rhizobiales, which are known for their ability to fix nitrogen in plants (Masson-Boivin et al, 2009).…”