The Microbiome of Pinus muricata Ectomycorrhizae: Community Assemblages, Fungal Species Effects, and Burkholderia as Important Bacteria in Multipartnered Symbioses

Bacteria have been observed to grow with fungi, and those that associate with ectomycorrhizal fungi have often been thought of as symbionts that may either increase or decrease ectomycorrhizal formation rate or provide other unaccounted benefits. To explore this symbiosis from a community ecology perspective, we sampled ectomycorrhizal root tips over a 3-year period and used 454 pyrosequencing to identify the bacteria that live inside the ectomycorrhizal root tips. The results showed that fungal community composition within the same soil core and fungal taxonomic identity had a stronger effect on bacterial community composition than sample year or site. Members of the Burkholderiales and Rhizobiales were most highly represented, reflecting many previous reports of these bacteria in association with fungi. The repeated occurrences of these two bacterial orders suggest that they may be symbiotic with their fungal hosts, although the nature of such mechanisms, be it symbiotic diazotrophy or otherwise, remains to be thoroughly tested.