VARIATION IN POLY-BETA-HYDROXYBUTYRATE SYNTHESIS IN RHIZOBIA REFLECTSSTRAIN DIFFERENTIATION AND TEMPERATURE REGULATION

Poly-beta-hydroxybutyrate (PHB), a carbon storage polymer, occurs wide ly among prokaryotes including Rhizobium. Screening of 45 strains of r hizobia, isolated from nodules of legumes inhabiting different ecologi cal regimes, showed a wide range of variation in the PHB content. Broa dly, this variation is strain- specific and may be used as a taxonomic character for strain differentiation. Rhizobia show minimum PHB conte nt at optimum temperature for growth and relatively higher content at the temperature extremes implying that PHB accumulation in rhizobia is in response to stress imposed by the extremes of temperature. PHB pre sumably protects membrane structure of rhizobia during this stress.