Acid Tolerance in Root Nodule Bacteria

  1. Derek J. Chadwick Organizer and
  2. Gail Cardew
  1. A. R. Glenn,
  2. W. G. Reeve,
  3. R. P. Tiwari and
  4. M. J. Dilworth

Published Online: 28 SEP 2007

DOI: 10.1002/9780470515631.ch8

Novartis Foundation Symposium 221 - Bacterial Responses to Ph

Novartis Foundation Symposium 221 - Bacterial Responses to Ph

How to Cite

Glenn, A. R., Reeve, W. G., Tiwari, R. P. and Dilworth, M. J. (2007) Acid Tolerance in Root Nodule Bacteria, in Novartis Foundation Symposium 221 - Bacterial Responses to Ph (eds D. J. Chadwick and G. Cardew), John Wiley & Sons, Ltd., Chichester, UK. doi: 10.1002/9780470515631.ch8

Author Information

  1. Centre for Rhizobium Studies, School of Biological Sciences and Biotechnology, Division of Science, Murdoch University. Murdoch, Perth, Western Australia, 6150, Australia

  1. Office of the Pro Vice Chancellor, University of Tasmania, Hobart, Tasmania, 7001, Australia.

Publication History

  1. Published Online: 28 SEP 2007

ISBN Information

Print ISBN: 9780471985990

Online ISBN: 9780470515631



  • acid tolerance;
  • root nodule bacteria;
  • calcium concentration;
  • Rhizobia;
  • pH-regulated structural gene


Biological nitrogen fixation, especially via the legume–Rhizobium symbiosis, is important for world agriculture. The productivity of legume crops and pastures is significantly affected by soil acidity; in some cases it is the prokaryotic partner that is pH sensitive. Growth of Rhizobium is adversely affected by low pH, especially in the ‘acid stress zone’. Rhizobia exhibit an adaptive acid tolerance response (ATR) that is influenced by calcium concentration. Using Tn5-mutagenesis, gusA fusions and ‘proteome’ analysis, we have identified a range of genes that are essential for growth at low pH (such as actA, actP, exoR, actR and actS). At least three regulatory systems exist. The two-component sensor–regulator system, actSR, is essential for induction of the adaptive ATR. Two other regulatory circuits exist that are independent of ActR. One system involves the low pH-induced regulator gene, phrR, which may control other low pH-regulated genes. The other circuit, involving a regulator that is yet unidentified, controls the expression of a pH-regulated structural gene (lpiA). We have used pH-responsive gusA fusions to identify acid-inducible genes (such as lpiA), and then attempted to identify the regulators of these genes. The emerging picture is of a relatively complex set of systems that respond to external pH.