Abstract
The presence of dry and mucoid colonies in cultures of rhizobial strains used in the production of commercial Australian inoculants is of concern for quality assurance because of the possibility of altered capacity for nodulation and nitrogen fixation by the different colony types. In this study, single colony isolates obtained from dry and mucoid colonies present in commercial cultures of Sinorhizobium meliloti were investigated to identify stability in culture, genetic identity and changes in exopolysaccharide (EPS) production, nodulation and nitrogen fixation. The 2 strains studied were WSM688 and WSM826 (Australian inoculant strains for annual and perennial medics, respectively), both of which produced only mucoid colonies on agar media when originally isolated from nodules. Dry and mucoid single colony isolates from the ‘mother cultures’ of the 2 strains exhibited stable colony phenotypes during successive subculturing in our laboratory and were shown to be most closely related to S. meliloti using 16S rRNA partial sequencing. All isolates produced at least 1 of 3 exopolysaccharides (succinoglycan, EPS II and K antigen) that are required for successful nodulation of Medicago species by S. meliloti strains, as indicated by nodulation of host legumes. Strain WSM826 isolates probably produce succinoglycan, as shown by similarity to the succinoglycan-producing strain Rm1021 in a calcofluor binding assay. In contrast to published work, there was no evidence that loss of mucoidy in dry colony isolates of either strain was associated with the presence of an insertion sequence element in the expR gene that inhibits EPS II production. For strain WSM688, dry and mucoid isolates were identical by PCR fingerprinting and showed a similar capacity to nodulate and fix nitrogen with the target host legume M. truncatula in glasshouse tests. In contrast, strain WSM826 mucoid isolates produced PCR fingerprints that were different from each other and from the WSM826 dry colony isolates. Dry and mucoid colonies may have arisen from substantial genetic change or through contamination of cultures by other S. meliloti strains. One WSM826 mucoid isolate (826-3) produced significantly lower shoot dry weight when inoculated onto both the target host M. sativa and non-target host M. truncatula, even though the capacity to nodulate both hosts was retained. This suggests that this isolate was affected in its nitrogen fixation capacity. Further research is required to identify the origin and extent of colony variation in commercial S. meliloti cultures.
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Claims 12
Claim · model-written summary
Dry and mucoid isolates retained stable colony phenotypes through subculturing.
MedicagoOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“Dry and mucoid single colony isolates from the ‘mother cultures’ of the 2 strains exhibited stable colony phenotypes during successive subculturing in our laboratory”
Claim · model-written summary
The isolates were most closely related to S. meliloti by partial 16S rRNA sequencing.
- Interactor
- S. meliloti
Sinorhizobium melilotie0symbiont - Outcome
- most closely related to S. melilotie0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“were shown to be most closely related to S. meliloti using 16S rRNA partial sequencing”
Claim · model-written summary
All isolates produced at least one of three exopolysaccharides needed for Medicago nodulation.
- Interactor
- S. melilotiSinorhizobium melilotie0symbiont
- Outcome
- at least 1 of 3 exopolysaccharidese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“All isolates produced at least 1 of 3 exopolysaccharides (succinoglycan, EPS II and K antigen) that are required for successful nodulation of Medicago species by S. meliloti strains”
Claim · model-written summary
WSM826 isolates probably produce succinoglycan.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“Strain WSM826 isolates probably produce succinoglycan, as shown by similarity to the succinoglycan-producing strain Rm1021 in a calcofluor binding assay”
Claim · model-written summary
Loss of mucoidy was not associated with an expR insertion sequence in dry isolates of either strain.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“there was no evidence that loss of mucoidy in dry colony isolates of either strain was associated with the presence of an insertion sequence element in the expR gene”
Claim · model-written summary
WSM688 dry and mucoid isolates had identical PCR fingerprints.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“For strain WSM688, dry and mucoid isolates were identical by PCR fingerprinting”
Claim · model-written summary
WSM688 dry and mucoid isolates had similar nodulation and nitrogen fixation capacity with M. truncatula.
- Taxon
- M. truncatula
Medicago truncatulae0 - Interactor
- WSM688e0symbiont
- Outcome
- similar capacity to nodulate and fix nitrogene0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“For strain WSM688, dry and mucoid isolates were identical by PCR fingerprinting and showed a similar capacity to nodulate and fix nitrogen with the target host legume M. truncatula in glasshouse tests”
Claim · model-written summary
WSM826 mucoid isolates had different PCR fingerprints from one another and from dry isolates.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“strain WSM826 mucoid isolates produced PCR fingerprints that were different from each other and from the WSM826 dry colony isolates”
Claim · model-written summary
Inoculation with WSM826 isolate 826-3 significantly lowered shoot dry weight of M. sativa.
- Taxon
- M. sativa
Medicago sativae0 - Treatment
- inoculatede0
- Interactor
- WSM826 mucoid isolate (826-3)e0symbiont
- Outcome
- shoot dry weighte0
- Direction
- lowere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“One WSM826 mucoid isolate (826-3) produced significantly lower shoot dry weight when inoculated onto both the target host M. sativa and non-target host M. truncatula”
Claim · model-written summary
Inoculation with WSM826 isolate 826-3 significantly lowered shoot dry weight of M. truncatula.
- Taxon
- M. truncatulaMedicago truncatulae0
- Treatment
- inoculatede0
- Interactor
- WSM826 mucoid isolate (826-3)e0symbiont
- Outcome
- shoot dry weighte0
- Direction
- lowere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“One WSM826 mucoid isolate (826-3) produced significantly lower shoot dry weight when inoculated onto both the target host M. sativa and non-target host M. truncatula”
Claim · model-written summary
WSM826 isolate 826-3 retained capacity to nodulate both Medicago hosts.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“One WSM826 mucoid isolate (826-3) produced significantly lower shoot dry weight when inoculated onto both the target host M. sativa and non-target host M. truncatula, even though the capacity to nodulate both hosts was retained”
Claim · model-written summary
Reduced shoot weight suggests WSM826 isolate 826-3 had impaired nitrogen fixation capacity.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“rhizobial inoculant strains for Medicago species”
e0“This suggests that this isolate was affected in its nitrogen fixation capacity.”
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See all 137 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.