Pine Wilt Disease: insights into the Biology of Bursaphelenchus xylophilus-associated bacteria.

Abstract

Pine wilt disease (PWD) is caused by the parasitic nematode Bursaphelenchus xylophilus (pinewood nematode; PWN), which infects mainly Pinus spe- cies with the aid of an insect-vector, Monochamus sp.. Bacteria isolated from B. xylophilus are being con- sidered as a fourth element in this disease complex. Their precise roles of these organisms in this interac- tion are unclear, as both beneficial and pathogenic bacteria have been found associated with PWD. Previously, we have shown the high oxidative stress tolerance of the PWN-associated bacteria Serratia sp. LCN16 and Serratia marcescens PWN146, and their beneficial effects towards the nematode under harsh oxidative stress conditions. Here, we present a de- tailed analysis of the genome sequences of these two PWN-associated bacteria and provide new insights into their biology and contributions to PWD and the PWN. Serratia sp. LCN16 is phylogenetically most closely related to the phytosphere group of Serratia, and shares many features with endophytes (plant- associated bacteria). These include genes coding for plant polymer degrading enzymes, iron uptake/ transport, siderophore and phytohormone synthesis, aromatic compound degradation and detoxification enzymes. Serratia marcescens PWN146 can also with- stand and colonize the plant environment, without having any deleterious effects towards B. xylophilus nor to the nematode model C. elegans. PWN146 has the potential to interfere with plant metabolism via hormonal pathways or nutritional acquisition (i.e. iron), and to be competitive against other bacteria and fungi, through resource acquisition or produc- tion of antimicrobial compounds.