Bio thermokinetic responses during the synthesis of poly 3 hydroxybutyrate by microbial co culture

Abstract

Metabolic heat from microbial cultures is proved to be an useful and highly accurate parameter for understanding bioprocesses. Metabolic heat could not only be used to track but also to quantitatively interpret the biological processes of the microbial system. Biopolymer demand continues to increase overtime. Poly(3-hydroxybutyrate) (PHB) is an important member of polyhydroxyalkanoates (PHA) which has potential applications in medical field. PHB is stored as the intracellular storage material within the microbial cells. Nonetheless, commercial production PHB could only be very successful if the PHB yield is high. An attempt has been made in this study to produce PHB through co-cultivation of Ralstoniaeutropha MTCC 2487, Pseudomonas putida MTCC 2475 and Azotobacter vinelandii MTCC 2459 (three soil dwelling microbial strains) in a bioreaction calorimeter (BioRC1e). In the shake flask studies with the optimized medium compositions and process conditions, co-culture resulted in maximum Cell Dry Mass (CDM) of 10.20 ± 0.50 g/L and PHB concentration of 6.32 ± 0.30 g/L when compared to the monoculture and pairwise cultures. PHB (product) yield coefficients due to CDM (YP/X), CDM yield due to substrate (YX/S) and PHB yield coefficient due to substrate (YP/S) are 0.62, 0.47 and 0.29 for co-cultivation strategy and it is higher when compared to monoculture and pairwise culture in the shake flask. In the Biocalorimeteric investigations (BioRC1e), aeration andagitation studies revealed that 1 Liter per minute (lpm) and 150 Rotations per minute (rpm) is optimal for higher productivity of PHB from the glucose assimilation. The volumetric mass transfer coefficient (kLa) observed in this study for 1 lpm aeration and 150 rpm agitation experiment was 674.81±32 h-1 , establishes that oxygen transfer to the cells was very useful. Metabolic peakheat for the co-culture obtained was 4.28 ± 0.09 W. Co-culture shows faster depletion of Nitrogen source (ammonium sulphate) in comparison with the pure cultures which resulted a 2.5 fold incr