Fermentation optimization for the production of poly(β-hydroxybutyric acid) microbial thermoplastic

Abstract

Batch culture of Alcaligenes latus, American Type Culture Collection 29713, was investigated for producing the intracellular bioplastic poly(␤-hydroxybutyric acid) (PHB). A central, composite experimental design was used to optimize the composition of the culture medium for maximizing the productivity of PHB. Investigated were the effects of temperature, the initial culture pH, the ionic strength of the medium, the concentration of trace elements, the type of nitrogen source, and the carbon-to-nitrogen ratio. The optimal temperature for growth and PHB synthesis appeared to be 33°C; however, over the 25-37°C range, the effect of temperature was negligible. An initial pH value of 6.5 gave the best results; pH values that differed even slightly from the optimum reduced the culture performance. Typical culture characteristics were: 0.075/h maximum specific growth rate, 0.38 g/l h maximum specific sucrose consumption rate, and 0.15 g/l h maximum specific PHB production rate. PHB was lost because of hydrolysis in the stationary phase, suggesting critical importance of timing the harvest. Under the best conditions, PHB constituted up to 63% of dry cell mass after 93 h of culture. The average biomass yield coefficient on sucrose was about 0.4 kg/kg. Of the four nitrogen sources-ammonium chloride, ammonium sulfate, ammonium nitrate, and urea-used, only the first two supported the culture satisfactorily. The biomass and PHB showed clear yield maxima at 1.5 g/l ammonium chloride (C:N ratio ϭ 21.5) and 1.4 g/l ammonium sulfate (C:N ratio ϭ 28.3). The yields were higher with ammonium sulfate and were relatively more sensitive to changes in its concentration. Ionic strength had a strong negative effect on PHB productivity. The highest PHB yield occurred at 4 g/l phosphate buffer concentration. Iron appeared to have the potential to enhance the proportion of PHB in the cells.

Production of poly-β-hydroxybutyrate (PHB) by Alcaligenes latus from maple sap

“…latus (ATCC 29714) was acquired from the ATCC collection and maintained on agar slants and Petri dishes on the Mineral Medium 1018 (Grothe et al 1999). The inocula were prepared in two steps: Several colonies of A. latus were used to inoculate a 50-mL Falcon tube containing 5 mL of sterilized nutrient broth medium (BD 234000, Difco) containing 5 g/L peptone and 3 g/L beef extract.…”

“…This strain was chosen because it uses sucrose, the main sugar in maple sap, effectively for growth and for PHB production (Palleroni and Palleroni 1978;Wang and Lee 1997;Grothe et al 1999), and it can be easily lysed to enhance the recovery of PHB (Byrom 1990). …”

Production of lovastatin by Aspergillus terreus: effects of the C:N ratio and the principal nutrients on growth and metabolite production

“…Selection and composition optimization of a suitable medium is therefore important for establishing a process for producing lovastatin. Various statistical experimental design strategies are widely used for optimizing fermentation media [13]. Of the major culture nutrients, carbon and nitrogen sources generally play a dominant role in fermentation productivity because these nutrients are directly linked with the formation of the biomass and the metabolite.…”

Potential Utilization of Pineapple Waste Streams for Polyhydroxyalkanoates (PHAs) Production via Batch Fermentation

“…The minimal medium was prepared following the procedure described by Grothe et al (1999) and Atlas (2004). The composition in a litre contains 1. .…”