Production of poly-beta-hydroxybutyrate (PHB) by Rhizobium meliloti, R-viciae and Bradyrhizobium japonicum with different carbon and nitrogen sources, and inexpensive substrates

Abstract

The capacities for poly-p-hydroxybutyrate synthesis were tested by strains of Rhizobium meliloti Y11, Rhizobium viciae F111 and Bradyrhizobium japonicum S Irat Fab during growth on media with different carbon and nitrogen sources, sugarbect molasses, and whey. The maximum yield for R. meliloti Y11 and B. japonicum S Irat Fab strains were 83.75% and 34.31% PHB on dry cell mass respectively, when they were grown in glucose. R. viciae F I I I produced a high level of PHB (41.22%) with mannitol. Generally, the PHB yield by the strains (except F111) was not found to be high in the media containing nitrogen sources. It was found that the three bacteria strains did not grow well and produce polymer in whey, but PHB was produced in all molasses concentrations. Among the strains, the highest PHB accumulation was obtained with strain Y11. The PHB content in cells with this strain reached 56.31% of dry cell mass during growth on 0.5% molasses concentration (0.5 molasses/100 mL solution). It was shown that the production of PHB decreased as a result of the increase in the incubation period. If the culture conditions are optimized, R. meliloti Y11 can be a good candidate for industrial PHB production from sugarbeet molasses and probably other inexpensive substrates.