Belated day 09 of the Microbial Advent Calendar, today we have a look at the Pine Microbiome. Trees are covered with bacteria and in some cases are intimately associated with some, often at the root level. Endophytic bacteria, located within the plant for at least part of its life cycle without causing apparent disease, have been shown to provide different services to the plants. Besides acting as plant growth promoters, they can exhibit strong anti-fungal activity, antagonise bacterial pathogens and control plant parasitic nematodes.
In North America, pine trees are subject to the pine wilt disease and since the late 90s the disease has spread to Europe. The disease is caused by a nematode, Bursaphelenchus xylophilus, which is inoculated into trees via insect vectors. Once in the wood, the tiny worm destroys the vascular system of the tree and can cause the death of its host within a few weeks. In the right conditions, B. xylophilus can reproduce quickly and infect a whole population of pines within months. The nematode is considered to be the main agent of the pine wilt disease.
A recent study (here) by Proença et al., looked at the microbiome of healthy pine trees as well as trees associated with the pine wilt disease at different stages. They also sampled trees in two different locations in Portugal. The first observation was that the microbial communities of wood colonizing bacteria were different on the two sampling sites. However, they observed in both sites an increase of the bacterial diversity as the trees progress through the different stage of the disease.
They postulate that in addition to the worm infection, a population of soil bacteria and opportunistic pathogens are colonizing the wood as the tree is getting progressively weaker. This disruption of the microbiome could also be a non-negligible factor of the pine wilt disease.