Present address: Supriya V. Kadam, Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA.
Poly-3-hydroxybutyrate (PHB) supports survival and reproduction in starving rhizobia
Article first published online: 8 JUL 2008
© 2008 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved
FEMS Microbiology Ecology
Volume 65, Issue 3, pages 391–399, September 2008
How to Cite
Ratcliff, W. C., Kadam, S. V. and Denison, R. F. (2008), Poly-3-hydroxybutyrate (PHB) supports survival and reproduction in starving rhizobia. FEMS Microbiology Ecology, 65: 391–399. doi: 10.1111/j.1574-6941.2008.00544.x
Editor: Christoph Tebbe
- Issue published online: 7 AUG 2008
- Article first published online: 8 JUL 2008
- Received 27 December 2007; revised 19 March 2008; accepted 26 May 2008.First published online 8 July 2008.
The carbon that rhizobia in root nodules receive from their host powers both N2 fixation, which mainly benefits the host, and rhizobium reproduction. Rhizobia also store energy in the lipid poly-3-hydroxybutyrate (PHB), which may enhance rhizobium survival when they are carbon limited, either in nodules or in the soil between hosts. There can be a conflict of interest between rhizobia and legumes over the rate of PHB accumulation, due to a metabolic tradeoff between N2 fixation and PHB accumulation. To quantify the benefits of PHB to carbon-limited rhizobia, populations of genetically uniform rhizobia with high vs. low PHB (confirmed by flow cytometry) were generated by fractionating Sinorhizobium meliloti via density gradient centrifugation, and also by harvesting cells at early vs. late stationary phase. These rhizobia were starved for 165 days. PHB use during starvation was highly predictive of both initial reproduction and long-term population maintenance. Cultured S. meliloti accumulated enough PHB to triple their initial population size when starved, and to persist for c. 150 days before the population fell below its initial value. During the first 21 days of nodule growth, undifferentiated S. meliloti within alfalfa nodules accumulated enough PHB to support significant increases in reproduction and survival during starvation.