Formation and utilisation of carbon reserves by Rhizobium

The accumulation and utilisation of poly-β-hydroxybutyrate (PHB) and extracellular polysaccharide (ECPS) have been studied in Rhizobium NZP 2037 and it was found that PHB synthesis was slow during growth whereas ECPS formation was not affected. PHB synthesis only was dependent on the pH of the medium. PHB and ECPS were both used as carbon sources in the absence of other exogenous carbon. ECPS when given to starved cells as sole carbon source in the absence of nitrogen was used for PHB synthesis by the organism. In the presence of nitrogen ECPS was found to support growth. The extracellular breakdown of ECPS was demonstrated and was accompanied by the release of its constituent glucose. This was favoured by low pH.