The genome and genetics of a high oxidative stress tolerant Serratia sp. LCN16 isolated from the plant parasitic nematode Bursaphelenchus xylophilus.
BACKGROUND
Pine 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.


RESULTS
Serratia 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.


CONCLUSIONS
This 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.
NemaLab/ICAAM - Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Departamento de Biologia, Universidade de Évora, Núcleo da Mitra, Ap. 94, 7002-554, Évora, Portugal.|Department of Environmental Biology, College of Bioscience & Biotechnology, Chubu University, 1200 Matsumoto, Kasugai, Aichi, 487-8501, Japan.
Claudia S L
CS
Vicente
NemaLab/ICAAM - Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Departamento de Biologia, Universidade de Évora, Núcleo da Mitra, Ap. 94, 7002-554, Évora, Portugal.
Francisco X
FX
Nascimento
Department of Environmental Biology, College of Bioscience & Biotechnology, Chubu University, 1200 Matsumoto, Kasugai, Aichi, 487-8501, Japan.
Yoriko
Y
Ikuyo
Information and Computational Sciences group (PJAC), The James Hutton Institute, Invergowrie, Dundee, DD2 5DA, UK.
Peter J A
PJ
Cock
NemaLab/ICAAM - Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Departamento de Biologia, Universidade de Évora, Núcleo da Mitra, Ap. 94, 7002-554, Évora, Portugal.|Departamento de Ciências da Vida, Universidade Lusófona de Humanidades e Tecnologias, Lisboa, Portugal.
Manuel
M
Mota
Department of Environmental Biology, College of Bioscience & Biotechnology, Chubu University, 1200 Matsumoto, Kasugai, Aichi, 487-8501, Japan. koichihasegawa@isc.chubu.ac.jp.
Koichi
K
Hasegawa
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D055786:Gene Knockout Techniques; D016680:Genome, Bacterial; D006861:Hydrogen Peroxide / Q000737:chemistry; D018384:Oxidative Stress; D010544:Peroxidases / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D028223:Pinus / Q000382:microbiology / Q000469:parasitology; D010935:Plant Diseases / Q000382:microbiology*; D012705:Serratia / Q000145:classification / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D017187:Tylenchida / Q000382:microbiology*
D001426:Bacterial Proteins; D014157:Transcription Factors; D006861:Hydrogen Peroxide; D010544:Peroxidases; C081610:catalase-peroxidase, bacteria
Bursaphelenchus xylophilus; Catalase; Endophyte; Oxidative stress; OxyR; Pine wilt disease; Plant defenses; Reactive oxygen species; Serratia