Diversity-invasibility relationships were explored in the novel context of the colonization resistance provided by gut bacteria of the desert locust Schistocerca gregaria against pathogenic bacteria. Germ-free insects were associated with various combinations of one to three species of locust gut bacteria and then fed an inoculum of the pathogenic bacterium Serratia marcescens. There was a significant negative relationship between the resulting density of Serratia marcescens and the number of symbiotic gut bacterial species present. Likewise there was a significant inverse relationship between community diversity and the proportion of locusts that harboured Serratia. Host mortality was not negatively correlated with resistance to gut-invasion by Serratia marcescens, although there were significantly more deaths among pathogen fed germ-free insects than tri-associated gnotobiotes. The outcome is consistent with the predictions of community ecology theory that species-rich communities are more resistant to invasion than species-poor communities.

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Aims: Faecal pellets from germ-free locusts were used as culture media to determine the ability of locust gut bacteria to synthesize phenolic components of the locust cohesion pheromone. Methods and Results: Inoculation of germ-free faecal pellets with Pantoea agglomerans, a species commonly isolated from locusts, resulted in the release of large amounts of guaiacol and small amounts of phenol, both of which are components of the locust cohesion pheromone. Two other locust-derived species, Klebsiella pneumoniae pneumoniae and Enterobacter cloacae, also produced guaiacol from germ-free faecal pellets, but the opportunistic locust pathogen, Serratia marcescens, did not. The most likely precursor for guaiacol is the plant-derived vanillic acid, which is present in large amounts in the faeces of both conventional and germ-free locusts. Conclusions: These observations are consistent with previous ones, that locust gut bacteria are responsible for the production of components of the locust cohesion pheromone. Significance and Impact of the Study: These findings illustrate how an insect can adapt to make use of a common bacterial metabolite produced by one or more of its indigenous gut bacterial species. This observation has implications for our appreciation of insect gut microbiota interactions.

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Thermophilic Geobacillus spp. can efficiently hydrolyze hemicellulose polymers and are therefore of interest in biotechnological applications. Here we report the genome sequences of two hemicellulolytic strains, Geobacillus sp. CAMR12739 and CAMR5420.