Epsilon Open Archive

Abstract

Arbuscular mycorrhizal (AM) fungi and bacteria can interact synergistically to stimulate plant growth through a range of mechanisms that include improved nutrient acquisition and inhibition of fungal plant pathogens. These interactions may be of crucial importance within sustainable, low-input agricultural cropping systems that rely on biological processes rather than agrochemicals to maintain plant health. The first goal of the present work was to further develop and optimise a method, bromodeoxyuridine immunocapture, suitable for the identification of actively growing bacteria in soil containing abundant AM fungi. DNA was extracted from soil that had been incubated with BrdU for 2 days, and the DNA was isolated by immunocapture of the BrdU-containing DNA. The actively growing bacteria in the community were identified by 16S rRNA gene PCR amplification and DNA sequence analysis. One of the actively growing bacteria, Bacillus cereus strain VA1, was isolated from the soil, tagged with green fluorescent protein (GFP) and shown to clearly attach to AM fungal hyphae. It was subsequently shown, however, that this bacterial strain had preferences for non-vital AM fungal hyphae, whereas one of the control strains, Paenibacillus brasilensis PB177, actually showed greater attachment to vital hyphae. A second objective was to study the impact of specific AM fungi and plant type on the actively growing soil bacterial communities, by using the BrdU method in combination with a fingerprinting technique (e.g. terminal restriction fragment length polymorphism, T-RFLP). This microbiomics (e.g. molecular tools for analysis of complex microbial communities) approach revealed distinct differences in bacterial community composition within the treatments, and the putative identities of the dominant bacterial species, activated as a result of Glomus mosseae inoculation, were found to be mostly uncultured bacteria and Paenibacillus sp., indicating the great significance of using an approach not relying on the culturability of the bacteria. Finally, Paenibacillus brasilensis PB177, previously shown to be associated with AM fungi, was shown to inhibit growth of several phytopathogenic fungi. In summary, the results of these studies provide novel valuable insights to consider when developing combined microbial inocula (e.g. bacteria and AM fungi) for enhancing plant growth within sustainable agriculture in the future.