Non‐specific transient mutualism between the plant parasitic nematode, Bursaphelenchus xylophilus, and the opportunistic bacterium Serratia quinivorans BXF1, a plant‐growth promoting pine endophyte with antagonistic effects

Abstract

The aim of this study is to understand the biological role of Serratia quinivorans BXF1, a bacterium commonly found associated with Bursaphelenchus xylophilus, the plant parasitic nematode responsible for pine wilt disease. Therefore, we studied strain BXF1 effect in pine wilt disease. We found that strain BXF1 promoted in vitro nematode reproduction. Moreover, the presence of bacteria led to the absence of nematode chitinase gene (Bxcht-1) expression, suggesting an effect for bacterial chitinase in nematode reproduction. Nevertheless, strain BXF1 was unable to colonize the nematode interior, bind to its cuticle with high affinity or protect the nematode from xenobiotic stress. Interestingly, strain BXF1 was able to promote tomato and pine plant-growth, as well as to colonize its interior, thus, acting like a plant-growth promoting endophyte. Consequently, strain BXF1 failed to induce wilting symptoms when inoculated in pine shoot artificial incisions. This bacterium also presented strong antagonistic activities against fungi and bacteria isolated from Pinus pinaster. Our results suggest that B. xylophilus does not possess a strict symbiotic community capable of inducing pine wilt disease symptoms as previously hypothesized. We show that bacteria like BXF1, which possess plant-growth promoting and antagonistic effects, may be opportunistically associated with B. xylophilus, possibly acquired from the bacterial endophytic community of the host pine.

The extreme plant‐growth‐promoting properties ofPantoea phytobeneficialisMSR2 revealed by functional and genomic analysis

“…Strain MSR2 is able to produce increased levels of IAA, and possibly other phytohormones such as cytokinins (discussed below), that significantly impact the nodulation process (Miri et al, 2016;Nadzieja et al, 2018). In addition, strain MSR2 contains ACC deaminase activity, which facilitates the nodulation process of leguminous plants by decreasing inhibitory ethylene levels (Nascimento et al, 2016a;Nascimento et al, 2016b;Tavares et al, 2018;Nascimento et al, 2019b).…”

“…In addition, the strain was tested for its ability to grow in Yeast Mannitol Agar (HiMedia, India); to present motility by its growth in Sulphide Indole Motility (SIM) Medium (Sigma Aldrich, Germany); to produce indole-3-acetic acid (IAA), siderophores, extracellular enzymes (i.e. amylase, protease, esterase, lipase and cellulase), acetoin, nitrate/nitrite reduction (nitrate reduction test), phosphate solubilization, antibiotic resistance (30 μg ml −1 chloramphenicol, 50 μg ml −1 ampicillin, 50 μg ml −1 kanamycin and 10 μg ml −1 tetracycline), 4-aminobutyrate catabolism (GABA; 1 mM GABA as sole nitrogen source) and phytohormonedegrading abilities (1 mM IAA; 1 mM salicylic acid; 1 mM benzoic acid as sole carbon sources) as described elsewhere (Rashid et al, 2012;Nascimento et al, 2016a;Nascimento et al, 2016b;Nascimento et al, 2019a).…”

The expression of an exogenous ACC deaminase by the endophyteSerratia grimesiiBXF1 promotes the early nodulation and growth of common bean

“…Serratia grimesii BXF1 was found to be a generalist endophyte (pine, tomato, cucumber) with plant‐growth promoting abilities, however, it does not contain ACC deaminase activity or the acdS gene (Nascimento et al . ). Therefore, S. grimesii BXF1 was transformed with plasmid pRKACC containing the acdS gene of Pseudomonas sp.…”

“…The endophytic strain S. grimesii BXF1 was selected to test the effect of ACC deaminase in its ability to promote rhizobia nodulation and common bean growth. Serratia grimesii BXF1 was found to be a generalist endophyte (pine, tomato, cucumber) with plant-growth promoting abilities, however, it does not contain ACC deaminase activity or the acdS gene (Nascimento et al 2016b). Therefore, S. grimesii BXF1 was transformed with plasmid pRKACC containing the acdS gene of Pseudomonas sp.…”

“…Hence, bacterial endophytes are potentially of great agricultural importance. Serratia species have not only been described as PGPB but some strains are also endophytes capable of colonizing internal plant tissues, including root nodules (Gyaneshwar et al 2001;Taghavi et al 2009;Nascimento et al 2016b;Zaheer et al 2016).…”