Advances on the bacterial diversity and functionality of Platypus cylindrus - Quercus suber interaction

The ambrosia beetle Platypus cylindrus Fab. (Coleoptera: Curculionidae: Platypodinae) has been associated in Portugal with cork oak (Quercus suber) tree death since the 1980s. Although traditionally known as a secondary pest damaging stressed and dead trees, its aggressiveness changed over the last decades. Ambrosia beetle is an insect known for its interactions with several species of fungi aiming for the gain of biologic functions that facilitates its life cycle. How bacterial communities harbored by ambrosia beetle impact forest ecosystems is not yet well known. In oak species, some pathogenic bacteria are often associated with wood insect infestations. From P. cylindrus body and wood tree bored galleries, culture dependent methods led to the isolation of bacteria involved in wood degradation and beetle ecology and even a new bacterial cork oak pathogen. To complement colony isolation efforts for the identification of the beetle-cork oak associated bacterial community, the same samples were analyzed with 16S metabarcoding. Two distinct bacterial communities from beetle mycangia and wood galleries sharing the most abundant bacterial taxa were revealed. A group of genera from Enterobacterales and Bradyrhizobium prevailed in the samples from wood galleries. Comparison between ASVs and full 16S sequences allowed the identification of Pectobacteriaceae as the major taxon from unclassified Enterobacterales carried by the beetle. Prediction of metabolic pathways varying between wood galleries and beetle mycangia revealed upregulation in the galleries of carbohydrate and virulence factors. Together, these analyses efficiently compared the bacteriome from the wood galleries with the beetle mycangia, revealing different bacterial communities and specific ecological roles related to both the beetle and trees. Additionally, they gave insights into the comparability of culture-dependent and independent methods in bacteriome analysis.