Diversity and Function of Endo-Bacteria in Bursaphelenchus xylophilus from Pinus massoniana Lamb. in Different Regions

Xiao-Qin Wu,Yan-Mei Fu,Hong-Bin Liu

doi:10.3390/f11050487

Abstract

The pine wood nematode (PWN) Bursaphelenchus xylophilus is the pathogen that causes pine wilt disease (PWD), a devastating forest disease. PWN-associated bacteria may play a role in PWD. However, little is known about the endo-bacteria in PWN. We analyzed the diversity of endo-bacteria in nine isolates of PWNs from Pinus massoniana Lamb. in nine epidemic areas from three Chinese provinces by high-throughput sequencing of 16S rDNA and isolated and identified culturable endo-bacteria through construction of a 16S rDNA phylogenetic tree and Biolog microbial identification. We also examined the effects of endo-bacteria on PWN fecundity, antioxidant capacity, and virulence using sterile nematodes as a control. While the dominant endo-bacteria in PWNs from different regions exhibited no significant difference in the classification levels of class and genus, their proportions differed. Pseudomonas and Stenotrophomonas were highly abundant in all PWN isolates. A total of 15 endo-bacterial strains were successfully isolated and identified as six species: Stenotrophomonas maltophilia, Pseudomonas fluorescens, Kocuria palustris, Microbacterium testaceum, Rhizobium radiobacter, and Leifsonia aquatica. We also found that P. fluorescens significantly increased the egg production of PWN, and that both P. fluorescens and S. maltophilia enhanced the mobility of PWN under oxidative stress and reduced the content of reactive oxygen species by increasing antioxidant enzyme activity in PWN. These strains also accelerated the development of PWD, and P. fluorescens had a more beneficial effect on PWN than S. maltophilia. Diversity exists among the endo-bacteria in PWNs from different regions, and some endo-bacteria can promote PWN infestation by enhancing the fecundity and antioxidant capacity of the nematode. Our study contributes to clarifying the interaction between endo-bacteria and PWN.

Highlights

The pine wood nematode (PWN) Bursaphelenchus xylophilus is a widespread quarantine pest that causes a destructive forest disease, pine wilt disease (PWD), and results in massive ecological and financial losses in numerous parts of Asia and Europe, especially in China [1,2,3,4,5,6]
Janthinobacterium, Sphingomonas, and Herbaspirillum were mainly concentrated in the isolates JS12-01 and JS12-02; Pseudomonas was mainly concentrated in GD12-01 and GD12-02; Sphingobacterium and Luteolibacter were mainly concentrated in SC12-02; Stenotrophomonas was mainly concentrated in GD12-02, GD12-03, and SC12-01; Achromobacter was mainly concentrated in GD12-03 and SC12-01; and Sphingobium and Chryseobacterium were mainly concentrated in SC12-01, SC12-02, and SC12-03 (Figure 1b)
These results indicate that the community structure of endo-bacteria in PWNs from different regions varies greatly, there was no difference in the ten dominant genera

Summary

Introduction

The pine wood nematode (PWN) Bursaphelenchus xylophilus is a widespread quarantine pest that causes a destructive forest disease, pine wilt disease (PWD), and results in massive ecological and financial losses in numerous parts of Asia and Europe, especially in China [1,2,3,4,5,6]. With the development of molecular biology techniques, recent studies have focused on the genes and proteins related to PWN fecundity, stress resistance, and pathogenesis [8,9]. Forests 2020, 11, 487 a sperm protein BxMSP10 was essential for egg hatching and fecundity in PWN [10]. Autophagy was found to be crucial for the development, fecundity, stress resistance, and pathogenicity of PWN [11,12,13,14].

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Discussion

Conclusion