Arbuscular mycorrhizal fungi and bacteria: how to construct prokaryotic DNA-free genomic libraries from the Glomales

Spores of various arbuscular mycorrhizal fungal isolates were analyzed for DNA of prokaryotic origin by amplification of the 16S rRNA. This shows that the presence of bacteria is not restricted to certain taxa within the Glomales, but distributed over all genera. Further experiments revealed, however, that, although single Glomus mosseae spores did not contain bacteria, samples of a number of spores were still contaminated with prokaryotes. In order to obtain genomic libraries from two arbuscular mycorrhizal fungi nearly free of clones of prokaryotic sequences, DNA extracted from spores was purified on CsCl gradients and used for library construction. Polymerase chain reaction analysis with primers for rRNA genes showed that the libraries contained if at all, only very low amounts of clones originated from bacteria.