Commensal relationships between insects and their microbiota have been little studied and are not well understood.  However, recent studies have suggested that there are more of these relationships than previously thought.

Schistocerca gregaria, the desert locust

Schistocerca gregaria, the desert locust, is known to exploit the production of common metabolites by its indigenous gut flora (Charnley et al., 2000). One such chemical, guaiacol, is used as a key component in a pheromone which promotes the aggregating behaviour of this locust species. Some of the organisms found in the desert locust hind gut are Escherichia coli, Enterobacter liquefasciens, Klebsiella pneumoniae, Enterobacter cloacae, Pantoea agglomerans and various Gram positive cocci.

A more recent study by Charnley et al. (2010), investigates the effect of both starvation and insect age on the diversity of the gut microbiome of adult S. gregaria. Analysis of bacterial 16S rRNA sequences allowed the identification of species that are not culturable by incubation. However, only one novel uncultured member of the Gammaproteobacteria was identified, present in the commensal flora of locusts within all focus groups (fed, starved, young and old).

The results of this work suggested that diversity of the gut microflora in desert locusts increases with insect age and starvation. Whilst starved insects are more prone to disease, likely because they compromise on immune defense, an increase in the diversity of Gammaproteobacteria in the starved locust population may actually provide an improved defence due to their role in colonization resistance, whereby the presence of one species prevents colonization by another through competition.

This study indicates that the changes in the diversity profile of the gut microbiota in locusts may benefit the host in terms of colonization resistance against pathogens. Another recent study published in Nature earlier this year (Wang et al., 2010) explores the human gut microbial gene catalogue, or ‘metagenome’, describes the diversity of the human gut flora in terms of minimal gut bacterial genome and identifies a common ‘core’ of bacteria in healthy individuals. Overall, the study by Wang et al. found that a decrease in bacterial diversity in the human gut was associated with obesity and common bowel diseases.

Key Reference
Dillon RJ, Webster G, Weightman AJ, Charnley AK (2010) Diversity of gut microbiota increases with aging and starvation in the desert locust, Antonie van Leeuwenhoek, Vol. 97, pp. 69–77 DOI:10.1007/s10482-009-9389-5

Guest post by intern Catriona Smith