Mechanisms of bacterial selection in the mycosphere of Tricholomateous fungi

PhD ceremony: Mr. F.G.H. Boersma, 14.45 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Mechanisms of bacterial selection in the mycosphere of Tricholomateous fungi

Promotor(s): prof. J.D. van Elsas

Faculty: Mathematics and Natural Sciences

The study presented in this thesis thus focused on particular groups of soil bacteria that show a response to mycorrhizal fungi in field soil. In particular, the soil adjacent to the bundle directly underneath fungal fruiting bodies was taken as the target compartment. We surmised that this dense hyphal network presumably has a profound effect on the local microbial community, allowing bacteria that have the suitable cellular machinery to benefit from the niche and prevail in the community.

Hence, the work focussed on the extent to which particular bacteria are selected in the mycosphere, initially of Laccaria proxima, and later of Russula exalbicans as well.

Two bacterial groups were selected on the basis of assumptions, or preliminary data, about their prevalence and role in the mycosphere. These were the sphingomonads on the one hand (detected solely by direct molecular means), and a tight cluster of abundant isolates, identified as Variovorax paradoxus related organisms, on the other hand.

The focus was then on the elucidation of possible mechanisms that underly the selection of the latter group, as experiments could be performed with isolates in laboratory and soil microcosms.