Screening of root nodule bacteria for the production of polyhydroxyalkanoate (PHA) and the study of parameters influencing the PHA accumulation

Abstract

Twelve polyhydroxyalkanoate (PHA) producing microbes were isolated from root nodules of 8 leguminous plants belonging to two phyla: Proteobacteria and Firmicutes. One of the isolate VK-12 of genus Burkholderia showed the highest PHA accumulation (42% wt/wt) as compared to other isolates in mineral medium. The effect of different cultural and growth conditions were studied on isolate VK-12 in shake flasks for highest PHA accumulation. VK-12 showed highest PHA accumulation in sucrose and ammonium sulphate amongst other carbon and nitrogen sources tested in the medium. The medium containing sucrose and ammonium sulphate having C: N ratio of 39.72 gave the highest PHA accumulation. The optimum pH, temperature, inoculum concentration and incubation time for highest PHA accumulation were 7.0, 30°C, 10% and 48 h respectively. An overall increase in PHA accumulation from 42 to 63% wt/wt was obtained under optimised conditions. The PHA was characterised using gas chromatography-mass spectrometry (GC-MS). All the isolates produced poly (3-hydroxybutyrate) (PHB) except VK-9, which produced polymer poly (3-hydroxybutyrate-co-3-hydroxyvalerate).

Keywords: Polyhydroxyalkanoate (PHA), PHB-co-HV, root nodule bacteria, carbon sources, C: N ratio, characterization of PHA