الملخص

In this study, five isolates of Sinorhizobium meliloti were obtained from root nodules of alfalfa plants collected from agricultural soils of different regions of Nineveh governorate/Iraq. Local isolates, RW8, RW9, RW10, RW11 and RW12 incubated for periods 1, 2, 3, 4 and 5 days. Biomass (g/l), production of poly-β-hydroxybutyrate (g/l) and production percentage (of dry cell weight) were recorded. Results revealed that RW9 isolate was the best among isolates of S. meliloti.It gave the best production percentage of poly-β-hydroxybutyrate which reached 43.05 % when grown in YEM (Yeast Extract Mannitol Broth) medium two days of incubation, whereas maximum average of biomass production reached 1.97 g/l. The effect of addition of different carbon sources growth medium on poly-β-hydroxybutyrate production by S. meliloti isolate RW9 showed that glucose, as carbon source, promote the productivity of the polymer that reached to 65.07 % two days after incubation. The optimal concentration of glucose to support highest production was 2.0 % that enhance production to 82.55 %. The effect of addition of different nitrogen sources at 0.10 % concentration to YEM broth medium (supplemented with 2.0 % glucose) revealed that glutamic acid gave the best productivity which reached 86.51 % two days after incubation. The effective concentration of glutamic acid support the best productivity was the used concentration (0.10 %). According to the obtained results RW9 isolate which accumulated high level of poly-β-hydroxybutyrate may be superior to be employed in industrial production when this isolate grown in optimum conditions.