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Acid tolerance in root nodule bacteria
A R Glenn1, W G Reeve, R P Tiwari
1Centre for Rhizobium Studies, School of Biological Sciences and Biotechnology, Murdoch University, Perth, Australia.
Novartis Foundation Symposium
|April 20, 1999
Summary
Biological nitrogen fixation relies on Rhizobium bacteria, which are sensitive to soil acidity. Researchers identified key genes and regulatory systems, including the ActSR two-component system, enabling Rhizobia to adapt to low pH conditions.
Area of Science:
- Agricultural Microbiology
- Plant-Microbe Interactions
- Bacterial Physiology
Background:
- Biological nitrogen fixation via legume Rhizobium symbiosis is crucial for global agriculture.
- Soil acidity significantly impacts legume crop and pasture productivity, often by affecting the Rhizobium symbiont.
- Rhizobia exhibit an adaptive acid tolerance response (ATR) influenced by calcium concentration, crucial for survival in acidic soils.
Purpose of the Study:
- To identify genes essential for Rhizobium growth under low pH conditions.
- To elucidate the regulatory systems governing the adaptive acid tolerance response (ATR) in Rhizobia.
- To understand how Rhizobia respond to and adapt to external pH stress.
Main Methods:
- Tn5-mutagenesis and gusA fusions were employed to identify acid-inducible genes.
- Proteome analysis was used to analyze gene expression under low pH stress.
- Identification of regulatory genes and circuits involved in pH response.
Main Results:
- Several genes essential for low pH growth were identified (e.g., actA, actP, exoR, actR, actS).
- The ActSR two-component sensor-regulator system is critical for inducing the adaptive ATR.
- Two independent regulatory circuits, involving phrR and an unidentified regulator, control other pH-responsive genes like lpiA.
Conclusions:
- Rhizobia possess a complex regulatory network to manage external pH stress.
- Understanding these acid tolerance mechanisms is vital for improving legume-based agriculture in acidic soils.
- The identified genes and regulatory systems provide targets for enhancing Rhizobium resilience and function.