Bacterial community structure associated with roots of Pinus montezumae Lamb. inoculated with edible ectomycorrhizal fungi and mycorrhizal helper bacteria

Tree roots are associated with a high diversity of microorganisms that play key roles in soil fertility and plant nutrition and health. Here we examine the composition and diversity of bacterial community in ectomycorrhizal root (ECR) and their ectomycorrhizosphere (EMR) of the Neotropical tree Pinus montezumae inoculated with Laccaria laccata and Hebeloma mesophaeum, applied alone or co-inoculated with Azospirillum brasilense. For this, we used a 16S rRNA gene metabarcoding-sequencing approach in samples of ECR and EMR that were collected nine-months after inoculation in greenhouse. A total of 943 Operational Taxonomic Units (OTU) were differentiated and grouped in 32 bacterial phyla. The most abundant phyla were Proteobacteria (67%) and Actinobacteria (20.7%). Bacterial communities were structured in ECR and EMR (Anosim, R=0.77, P≤0.005), and were more diverse in EMR than ECR (Shannon-Weaver of 4.2 and 3.6, and Simpson inverse of 33.7 and 16.7, respectively). The abundance of Pseudomonas, Actinoplanes and Salinibacterium were promoted with L. laccata, while with H. mesophaeum an OTU from Burkholderiaceae was prominent. Our results showed that the ectomycorrhizal fungi strongly shaped the composition of the bacterial communities associated with roots of P. montezumae.