Abstract
Termites host a gut microbiota of diverse and essential symbionts that enable specialization on dead plant material; an abundant, but nutritionally imbalanced food source. To supplement the severe shortage of dietary nitrogen (N), some termite species make use of diazotrophic bacteria to fix atmospheric nitrogen (N2). Fungus-growing termites (subfamily Macrotermitinae) host a fungal exosymbiont (genus Termitomyces) that provides digestive services and the main food source for the termites. This has been thought to obviate the need for N2-fixation by bacterial symbionts. Here, we challenge this notion by performing acetylene reduction assays of live colony material to show that N2 fixation is present in two major genera (Macrotermes and Odontotermes) of fungus-growing termites. We compare and discuss fixation rates in relation to those obtained from other termites, and suggest avenues of research that may lead to a better understanding of N2 fixation in fungus-growing and other termites.
Highlights
The success of termites has been attributed to their ability to consume nutritionally imbalanced food sources, allowing them to exploit otherwise inaccessible niches (Brune, 2014)
N2 fixation has been thought to be absent or insignificant in fungus-growing termites, as their access to N is hypothetically nutritionally less constrained than that of other termites (Higashi et al, 1992; Eggleton and Tayasu, 2001). Considering those hypotheses and recent work suggesting that different castes of fungusgrowing termites may have different nutritional requirements as they have distinct diets and gut microbiota (Hongoh et al, 2006), we examined whether symbiotic N2-fixation takes place in fungus-growing termites by performing acetylene reduction assay (ARA) on two termite species, M. natalensis and Odontotermes badius
Work using the ARA demonstrated that N2 fixation is present (Benemann, 1973; Breznak et al, 1973), that rates are highest in workers, and that fixation is performed by gut bacteria (French et al, 1976)
Summary
The success of termites has been attributed to their ability to consume nutritionally imbalanced food sources, allowing them to exploit otherwise inaccessible niches (Brune, 2014). N2 fixation has been thought to be absent or insignificant in fungus-growing termites, as their access to N is hypothetically nutritionally less constrained than that of other termites (Higashi et al, 1992; Eggleton and Tayasu, 2001). Considering those hypotheses and recent work suggesting that different castes of fungusgrowing termites may have different nutritional requirements as they have distinct diets and gut microbiota (Hongoh et al, 2006), we examined whether symbiotic N2-fixation takes place in fungus-growing termites by performing ARA on two termite species, M. natalensis and Odontotermes badius. We compare our findings with previous work on members of other termite sub-families and suggest that diazotrophic fixation should be considered present in this subfamily
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