Abstract
Sinorhizobium meliloti associates with Medicago and Melilotus species to develop nitrogen-fixing symbioses. The agricultural relevance of these associations, the worldwide distribution of acid soils, and the remarkable acid sensitivity of the microsymbiont have all stimulated research on the responses of the symbionts to acid environments. We show here that an adaptive acid-tolerance response (ATR) can be induced in S. meliloti, as shown previously for Sinorhizobium medicae, when the bacteria are grown in batch cultures at the slightly acid pH of 6.1. In marked contrast, no increased tolerance to hydrogen ions is obtained if rhizobia are grown in a chemostat under continuous cultivation at the same pH. The adaptive ATR appears as a complex process triggered by an increased hydrogen-ion concentration, but operative only if other--as yet unknown--concomitant factors that depend on the culture conditions are present (although not provided under continuous cultivation). Although the stability of the ATR and its influence on acid tolerance has been characterized in rhizobia, no data have been available on the effect of the adapted state on symbiosis. Coinoculation experiments showed that acid-adapted indicator rhizobia (ATR+) were present in >90% of the nodules when nodulation was performed at pH 5.6, representing a >30% increase in occupancy compared with a control test. We show that the ATR represents a clear advantage in competing for nodulation at low pH. It is not yet clear whether such an effect results from an improved performance in the acid environment during preinfection, an enhanced ability to initiate infections, or both conditions. The practical use of ATR+ rhizobia will depend on validation experiments with soil microcosms and on field testing, as well as on the possibility of preserving the physiology of ATR+ bacteria in inoculant formulations.
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Claims 4
Claim · model-written summary
Batch culture at pH 6.1 induced acid tolerance in S. meliloti.
- Taxon
- alfalfa
Medicago sativat0 - Treatment
- batch cultures at the slightly acid pH of 6.1e0
- Interactor
- S. meliloti
Sinorhizobium melilotie0symbiont - Outcome
- adaptive acid-tolerance response (ATR)e0
- Direction
- inducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an adaptive acid-tolerance response (ATR) can be induced in S. meliloti, as shown previously for Sinorhizobium medicae, when the bacteria are grown in batch cultures at the slightly acid pH of 6.1.”
t0“alfalfa”
Claim · model-written summary
Continuous cultivation at pH 6.1 did not increase rhizobial tolerance to hydrogen ions.
- Taxon
- alfalfaMedicago sativat0
- Treatment
- grown in a chemostat under continuous cultivation at the same pHe0
- Interactor
- rhizobiae0symbiont
- Outcome
- tolerance to hydrogen ionse0
- Direction
- no increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“no increased tolerance to hydrogen ions is obtained if rhizobia are grown in a chemostat under continuous cultivation at the same pH.”
t0“alfalfa”
Claim · model-written summary
Acid adapted rhizobia occupied over 90% of alfalfa nodules at pH 5.6.
- Taxon
- alfalfaMedicago sativat0
- Treatment
- acid-adapted indicator rhizobia (ATR+)e0
- Interactor
- rhizobiae0symbiont
- Outcome
- occupancye0
- Direction
- increasee0
- Value
- >90%e0
- Qualifier
- pH 5.6e0
- Comparator
- a control teste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“acid-adapted indicator rhizobia (ATR+) were present in >90% of the nodules when nodulation was performed at pH 5.6, representing a >30% increase in occupancy compared with a control test.”
t0“alfalfa”
Claim · model-written summary
Acid adapted rhizobia increased nodule occupancy by over 30% compared with the control.
- Taxon
- alfalfaMedicago sativat0
- Treatment
- acid-adapted indicator rhizobia (ATR+)e0
- Interactor
- rhizobiae0symbiont
- Outcome
- occupancye0
- Direction
- increasee0
- Value
- >30%e0
- Qualifier
- pH 5.6e0
- Comparator
- a control teste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“acid-adapted indicator rhizobia (ATR+) were present in >90% of the nodules when nodulation was performed at pH 5.6, representing a >30% increase in occupancy compared with a control test.”
t0“alfalfa”
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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.