Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) with a broad range of 3HV content at high yields by Burkholderia sacchari IPT 189

The biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from sucrose and propionic acid by Burkholderia sacchari IPT 189 was studied using a two-stage bioreactor process. In the first stage, this bacterium was cultivated in a balanced culture medium until sucrose exhaustion. In the second stage, a solution containing sucrose and propionic acid as carbon source was fed to the bioreactor at various sucrose/propionic acid (s/p) ratios at a constant specific flow rate. Copolymers with 3HV content ranging from 40 down to 6.5 (mol%) were obtained with 3HV yield from propionic acid (Y-3HV/prop) increasing from 1.10 to 1.34 g g(-1). Copolymer productivity of 1 g l(-1) h(-1) was obtained with polymer biomass content rising up to 60% by increasing a specific flow rate at a constant s/p ratio. Increasing values of 3HV content were obtained by varying the s/p ratios. A simulation of production costs considering Y-3HV/prop obtained in the present work indicated that a reduction of up to 73% can be reached, approximating US$ 1.00 per kg which is closer to the value to produce P3HB from sucrose (US$ 0.75 per kg).

Screening of bacteria to produce polyhydroxyalkanoates from xylose

Although xylose is a major constituent of lignocellulosic feedstock and the second most abundant sugar in nature, only 22% of 3,152 screened bacterial isolates showed significant growth in xylose in 24 h. Of those 684, only 24% accumulated polyhydroxyalkanoates after 72 h. A mangrove isolate, identified as Bacillus sp. MA3.3, yielded the best results in literature thus far for Gram-positive strains in experiments with glucose and xylose as the sole carbon source. When glucose or xylose were supplied, poly-3-hydroxybutyrate (PHB) contents of cell dry weight were, respectively, 62 and 64%, PHB yield 0.25 and 0.24 g g(-1) and PHB productivity (P(PHB)) 0.10 and 0.06 g l(-1) h(-1). This 40% P(PHB) difference may be related to the theoretical ATP production per 3-hydroxybutyrate (3HB) monomer calculated as 3 mol mol(-1) for xylose, less than half of the ATP/3HB produced from glucose (7 mol mol(-1)). In PHB production using sugar mixtures, all parameters were strongly reduced due to carbon catabolite repression. PHB production using Gram-positive strains is particularly interesting for medical applications because these bacteria do not produce lipopolysaccharide endotoxins which can induce immunogenic reactions. Moreover, the combination of inexpensive substrates and products of more value may lead to the economical sustainability of industrial PHB production.