Burkholderia cepacia PHAs

C. necator is the model bacterium for the biosynthesis of PHA. This strain generally initiates the synthesis of PHA when either nitrogen or phosphorous is limited during growth (Kahar et al. 2004). A similar phenomenon occurs in several other PHA producers including Burkholderia cepacia (Zazali and Tan 2005 Mitomo et al. 1999), Pseudomonas sp. (Choi et al. 2003), and A. hydrophila... 

The following bacteria recombinant Ralstonia eutropha, Ralstonia eutro-pha, recombinant Escherichia coli, Burkholderia sacchari, Burkholderia cepacia, Azotobacter vinelanddi, Pseudomonas olevorans, Methylobacterium organophilum and Bacillus cereus have more favorable characteristics for industrial scale production. 

Culture and fermentation conditions. PHA production experiments were conducted in shake-flasks using cultures of Burkholderia cepacia, obtained from the American Type Culture Collection (ATCC No. 17759, Bethesda, MD). Cultures of B. cepacia were maintained at 25 C and transferred weekly on agar slants containing xylose (2.2 % w/v) and levulinic acid (0.3 % w/v) as carbon sources. Levulinic acid was added to cultures as a concentrated solution (pH adjusted to 7.2 via NaOH prior to sterilization). Inocula were prepared as 500-1000 ml cultures in 2,800 ml Fernbach flasks containing 2.2 % (w/v) xylose and 0.07 % (w/v) levulinic acid, incubated at 28 C and 150 rpm for 72 hours. For PHA production, shake-flasks were inoculated with a 5 % (v/v) aliquot of the above-described seed culture, incubated at 28 C and 150 rpm for 20 hours, and were then supplemented with a second dose (0-0.5 % w/v) of levulinic acid. Flasks were subsequently incubated for an additional 62-115 hours of growth in order to assess time-related differences in polymer production, and then harvested for biomass and PHA extraction, as previously described (20),... 

Figure 2. Time profiles of dry biomass, P(3HB-co-3HV) yields, and PHA contents for shake-flask cultures o/Burkholderia cepacia grow/ on detoxified aspen-derived hemicellulosic hydrolysate and 0.45 % (w/v) levulinic acid.

Burkholderia cepacia (formerly Pseudomonas cepacia), a Gram-negative bacterium, is able to utilize a wide variety of carbon sources and accumulate PHAs under nutrient-limiting conditions and excess carbon (Young et al. 1994 Ramsay et al. 1995). Ramsay et al. (1995) have shown its ability to utilize xylose on an ammonium-limited medium and produce P(3HB). Batch fermentation data showed that when xylose was the single substrate, the maximum specific P(3HB) production rate, the yield of P(3HB) produced from substrate consumed (Yphb/s). and the percentage of P(3HB) accumulated in the cells were 0.072 g/(g h), 0.11 g g and 45 % (w/w), respectively. These results were very similar to the ones published for this strain on fmctose. 

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