Competition Experiments for Legume Infection Identify Burkholderia phymatum as a Highly Competitive β-Rhizobium

Lardi, Martina; Campos, Samanta Bolzan de; Purtschert, Gabriela; Eberl, Leo; Pessi, Gabriella

doi:10.3389/fmicb.2017.01527

Cited by 39 publications

(56 citation statements)

References 78 publications

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“…strain). Considering that in our experiment the growing substrate was a mixture of vermiculate and river sand (therefore very poor regarding N content), our results are a confirmation of previous reports [25,26] which underlines that nitrogen-limited conditions favor the dominance of Burkholderia species over other rhizobial strains. Obviously, the higher number of nodules in Brh+ plants vs. Rh.l+ plants under saline conditions supports this finding.…”

Section: Discussionsupporting

confidence: 90%

Tripartite Relationships in Legume Crops Are Plant-Microorganism-Specific and Strongly Influenced by Salinity

Veselaj¹,

Sallaku

Balliu

2018

Agriculture

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This study investigated the effects of specific strains of two arbuscular mycorrhizae fungi (AMF) (Rhizophagus irregularis and Claroideoglomus claroideum) and of two plant growth-promoting bacteria (PGPB) (Rhizobium leguminosarum and Burkholderia spp.), supplied either individually or as combination of a mixture of both arbuscular mycorrhizae fungi with each bacteria on root morphology, growth and fresh grain yield in pea (Pisum sativum L.) plants. Inoculated and non-inoculated pea plants were subjected to two levels of salinity (0 and 50 mM) by the addition of sodium chloride into tap water. Prior to fresh grain harvesting the morphology of root system was analyzed and the dry matter of roots and shoots were individually measured in randomly selected plants. Fresh pods were individually harvested per each plant; fresh (green) grains were separately counted and weighted per each pod at each individual plant, and the average grain weight was calculated by dividing total grain weight of plant with the respective number of green grains. The raise of salinity in the irrigation water strongly diminished the growth of pea plants by significantly reducing weight, length, surface area and root volume of pea plants. The relationships of pea plants with beneficiary fungi and bacteria were specific to each microorganism and highly depended on the environment. We found that under saline conditions, Rhizophagus irregularis provided a better vegetative growth and a higher yield than Claroideoglomus claroideum. Although, single application of Burkolderia spp. provides a better vegetative growth than single application of Rhizobium leguminosarum the best results, in terms of growth and harvested yield, were still obtained by combined application of AM fungi with Rhizobium leguminosarum. This combination was able to sustain the average grain weight at the level of non-saline plants and provided a significantly higher yield than the control plants.

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Section: Discussionsupporting

confidence: 90%

Tripartite Relationships in Legume Crops Are Plant-Microorganism-Specific and Strongly Influenced by Salinity

Veselaj¹,

Sallaku

Balliu

2018

Agriculture

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“…Swimming motility, biofilm formation, and EPS production. Swimming motility was determined on plates of LB without salt supplemented with 0.1% Casamino Acids that were solidified with 0.2% agar and measured after 30 h of incubation as described previously (79). Overnight bacterial cultures (5 l) were spotted in the middle of plates and then incubated at 28°C for 30 h.…”

Section: Methodsmentioning

confidence: 99%

“…Exopolysaccharide (EPS) production by WT PsJN and variant forms was tested on mannitol medium containing 1% mannitol and 0.06% yeast extract (79).…”

Section: Methodsmentioning

confidence: 99%

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Biofilm-Constructing Variants of Paraburkholderia phytofirmans PsJN Outcompete the Wild-Type Form in Free-Living and Static Conditions but Not In Planta

Rondeau

Esmaeel

Crouzet

et al. 2019

Appl Environ Microbiol

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Members of the genus Burkholderia colonize diverse ecological niches. Among the plant-associated strains, Paraburkholderia phytofirmans PsJN is an endophyte with a broad host range. In a spatially structured environment (unshaken broth cultures), biofilm-constructing specialists of P. phytofirmans PsJN colonizing the air-liquid interface arose at high frequency. In addition to forming a robust biofilm in vitro and in planta on Arabidopsis roots, those mucoid phenotypic variants display a reduced swimming ability and modulate the expression of several microbe-associated molecular patterns (MAMPs), including exopolysaccharides (EPS), flagellin, and GroEL. Interestingly, the variants induce low PR1 and PDF1.2 expression compared to that of the parental strain, suggesting a possible evasion of plant host immunity. We further demonstrated that switching from the planktonic to the sessile form did not involve quorum-sensing genes but arose from spontaneous mutations in two genes belonging to an iron-sulfur cluster: hscA (encoding a cochaperone protein) and iscS (encoding a cysteine desulfurase). A mutational approach validated the implication of these two genes in the appearance of variants. We showed for the first time that in a heterogeneous environment, P. phytofirmans strain PsJN is able to rapidly diversify and coexpress a variant that outcompete the wild-type form in free-living and static conditions but not in planta. IMPORTANCE Paraburkholderia phytofirmans strain PsJN is a well-studied plantassociated bacterium known to induce resistance against biotic and abiotic stresses. In this work, we described the spontaneous appearance of mucoid variants in PsJN from static cultures. We showed that the conversion from the wild-type (WT) form to variants (V) correlates with an overproduction of EPS, an enhanced ability to form biofilm in vitro and in planta, and a reduced swimming motility. Our results revealed also that these phenotypes are in part associated with spontaneous mutations in an iron-sulfur cluster. Overall, the data provided here allow a better understanding of the adaptive mechanisms likely developed by P. phytofirmans PsJN in a heterogeneous environment.

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“…Nodule number, nodule dry weight, and nitrogenase activity were calculated as described previously [23,63]. Two independent experiments, with at least nine plants per strain, were performed.…”

Section: Methodsmentioning

confidence: 99%

Metabolomics and Transcriptomics Identify Multiple Downstream Targets of Paraburkholderia phymatum σ54 During Symbiosis with Phaseolus vulgaris

Lardi

Liu

Giudice

et al. 2018

IJMS

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RpoN (or σ54) is the key sigma factor for the regulation of transcription of nitrogen fixation genes in diazotrophic bacteria, which include α- and β-rhizobia. Our previous studies showed that an rpoN mutant of the β-rhizobial strain Paraburkholderia phymatum STM815T formed root nodules on Phaseolus vulgaris cv. Negro jamapa, which were unable to reduce atmospheric nitrogen into ammonia. In an effort to further characterize the RpoN regulon of P. phymatum, transcriptomics was combined with a powerful metabolomics approach. The metabolome of P. vulgaris root nodules infected by a P. phymatum rpoN Fix− mutant revealed statistically significant metabolic changes compared to wild-type Fix+ nodules, including reduced amounts of chorismate and elevated levels of flavonoids. A transcriptome analysis on Fix− and Fix+ nodules—combined with a search for RpoN binding sequences in promoter regions of regulated genes—confirmed the expected control of σ54 on nitrogen fixation genes in nodules. The transcriptomic data also allowed us to identify additional target genes, whose differential expression was able to explain the observed metabolite changes in numerous cases. Moreover, the genes encoding the two-component regulatory system NtrBC were downregulated in root nodules induced by the rpoN mutant, and contained a putative RpoN binding motif in their promoter region, suggesting direct regulation. The construction and characterization of an ntrB mutant strain revealed impaired nitrogen assimilation in free-living conditions, as well as a noticeable symbiotic phenotype, as fewer but heavier nodules were formed on P. vulgaris roots.

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Competition Experiments for Legume Infection Identify Burkholderia phymatum as a Highly Competitive β-Rhizobium

Cited by 39 publications

References 78 publications

Tripartite Relationships in Legume Crops Are Plant-Microorganism-Specific and Strongly Influenced by Salinity

Tripartite Relationships in Legume Crops Are Plant-Microorganism-Specific and Strongly Influenced by Salinity

Biofilm-Constructing Variants of Paraburkholderia phytofirmans PsJN Outcompete the Wild-Type Form in Free-Living and Static Conditions but Not In Planta

Metabolomics and Transcriptomics Identify Multiple Downstream Targets of Paraburkholderia phymatum σ54 During Symbiosis with Phaseolus vulgaris

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