Production of Polyhydroxyalkanoate (PHAs) and Copolymer [P(HB-co-HV)] by Soil Bacterial Isolates in Batch and Two-Stage Batch Cultures

NINETY TWO local bacterial isolates, from the rhizosphere and soil around the root system of bean (Vicia faba) grown in Kalubia Governorate in Egypt, were bio-prospected for polyhydroxyalkanoate (PHA) accumulation. Three isolates accumulated ≥ 20 % of PHAs, they were identified as Pseudomonas fluorescens S48, Bacillus megaterium 7A and B. megaterium UBF19. The tested isolates gave the maximum PHAs content on basal medium containing glucose and ammonium sulfate at C/N ratio of 30/1 after 72 hr at 30oC using shake flask culture technique. Two-stage batch were implemented with varying loading levels of nitrogen and phosphorus, inoculated with washed cells. Nitrogen omission of 70 % led to increase the PHAs content by 19 %, 3% and 8.5 % using washed cells of Ps. fluorescens S48, B. megaterium UBF19 and Bacillus megaterium 7A, respectively comparing with batch production on the same medium after 72 hr. The Copolymer poly(hydroxybutyrate-co-hydroxyvalerate) [P (HB-co-HV)] content level was increased when valeric/glucose (V/G) was 0.19 mol.mol-1 after 96 hr being 25.97 % and 20.11 % by Ps. fluorescens S48 and B. megaterium UBF19, respectively and reached 23.73 % by B. megaterium 7A at propionic/glucose (P/G) of 0.5 mol.mol-1. The corresponding highest values of valeric content of copolymer at V/G 3.08 mol.mol-1 were 63 %, 49 % and 45 %, respectively,comparing with other V/G ratios by using GC analysis . Replacing glucose with 2 % corn oil or 1 % soybean oil increased the PHAs content of Ps. fluorescens S48 cells to 54.21 % and 52.12 %, respectively, after 72 hr.