Abstract
BackgroundPine wilt disease (PWD) is a worldwide threat to pine forests, and is caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus. Bacteria are known to be associated with PWN and may have an important role in PWD. Serratia sp. LCN16 is a PWN-associated bacterium, highly resistant to oxidative stress in vitro, and which beneficially contributes to the PWN survival under these conditions. Oxidative stress is generated as a part of the basal defense mechanism used by plants to combat pathogenic invasion. Here, we studied the biology of Serratia sp. LCN16 through genome analyses, and further investigated, using reverse genetics, the role of two genes directly involved in the neutralization of H2O2, namely the H2O2 transcriptional factor oxyR; and the H2O2-targeting enzyme, catalase katA.ResultsSerratia sp. LCN16 is phylogenetically most closely related to the phytosphere group of Serratia, which includes S. proteamaculans, S. grimessi and S. liquefaciens. Likewise, Serratia sp. LCN16 shares many features with endophytes (plant-associated bacteria), such as genes coding for plant polymer degrading enzymes, iron uptake/transport, siderophore and phytohormone synthesis, aromatic compound degradation and detoxification enzymes. OxyR and KatA are directly involved in the high tolerance to H2O2 of Serratia sp. LCN16. Under oxidative stress, Serratia sp. LCN16 expresses katA independently of OxyR in contrast with katG which is under positive regulation of OxyR. Serratia sp. LCN16 mutants for oxyR (oxyR::int(614)) and katA (katA::int(808)) were sensitive to H2O2 in relation with wild-type, and both failed to protect the PWN from H2O2-stress exposure. Moreover, both mutants showed different phenotypes in terms of biofilm production and swimming/swarming behaviors.ConclusionsThis study provides new insights into the biology of PWN-associated bacteria Serratia sp. LCN16 and its extreme resistance to oxidative stress conditions, encouraging further research on the potential role of this bacterium in interaction with PWN in planta environment.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2626-1) contains supplementary material, which is available to authorized users.
Highlights
Pine wilt disease (PWD) is a worldwide threat to pine forests, and is caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus
Vicente et al [13] showed the importance of PWN catalases in hydrogen peroxide (H2O2) detoxification in vitro, and Espada et al [14] identified novel proteins involved in the host-parasite interaction and provided clear evidence that PWN employs a multilayered detoxification strategy to overcome plant defenses
The present study revealed the potential of PWNassociated bacteria Serratia sp
Summary
Pine wilt disease (PWD) is a worldwide threat to pine forests, and is caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus. The primary pathogenic agent of PWD is the plantparasitic nematode Bursaphelenchus xylophilus (pine wood nematode, PWN) [3, 4]. Shinya and co-workers [12] investigated the PWN secretome and identified a range of secreted cell-wall degrading enzymes and host-defense evasion proteins, among which 12 antioxidant enzymes (PRX, peroxiredoxin; CAT, catalase; GPX, glutathione peroxidase; nucleoredoxin-like proteins; SOD, superoxide dismutase; TRX, thioredoxin) were identified. Vicente et al [13] showed the importance of PWN catalases in H2O2 detoxification in vitro, and Espada et al [14] identified novel proteins involved in the host-parasite interaction and provided clear evidence that PWN employs a multilayered detoxification strategy to overcome plant defenses
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