Actinobacteria may influence white truffle (Tuber magnatum Pico) nutrition, ascocarp degradation and interactions with other soil fungi

• We isolated Rhodococcus sp. and Curtobacterium sp. from white truffle ascocarp.
• Actinobacteria performed carbon/nitrogen source dependant phosphate solubilisation.
• We isolated potentially fungicolous moulds from diseased white truffle ascocarp.
• Actinobacteria expressed specific interactions with ascocarp-inhabiting moulds.
• Actinobacteria may influence truffle nutrient acquisition and relation to soil fungi.

To test the hypothesis that truffle-associated bacteria may improve truffle nutrition, we isolated bacteria from white truffle ascocarps and tested Actinobacteria for their ability to solubilise phosphate and iron, nutrients that have limited availability in white truffle grounds. Two isolates with sequence similarities to Curtobacterium flaccumfaciens and Rhodococcus sp. were characterized in detail. Both solubilised Ca3(PO4)2 in a way that was dependent on the nitrogen and carbon sources present. Neither strain broke down phytate, but both produced chelating compounds, performed ammonification, and broke down β-glucan. Additionally, C. flaccumfaciens decomposed chitin, pectin, lipids and proteins, while Rhodococcus sp. exhibited urease activity. Three potentially fungicolous fungi were isolated from diseased white truffle ascocarps and bioassayed against the isolated Actinobacteria. The Rhodococcus isolate inhibited Verticillium leptobactrum, neither bacterium affected Clonostachys rosea, while both isolates promoted growth of Trichoderma sp. The results suggest that Actinobacteria might be involved in improving truffle nutrition, ascocarp degradation and establishing relationships with other soil fungi.