In this study, fed-batch fermentation of Haloferax mediterranei using glucose and yeast extract as carbon and nitrogen source, respectively, was carried out to produce poly(hydroxyalkanoate) (PHA). After fermentation for 117 h, the concentration of H. mediterranei and PHA content reached 85.8 g/l and 48.6%, respectively. 1H- and 13C-NMR spectra proved that the produced PHA was poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) co-polymer. However, further fractionation using chloroform/acetone revealed that the produced PHA consisted of at least two compositionally different co-polymers (P1 and P2). One P(3HB-co-3HV) co-polymer (P1, 93.4 wt%) contains 10.7 mol% of 3-HV unit in the chain structure and has a high molecular weight of 569.5 kg/mol. The other one (P2, 6.6 wt%) has a slightly higher 3-HV content, ca. 12.3 mol%, but its molecular weight is relatively low, 78.2 kg/mol. Both fractions exhibit two overlapped melting peaks measured by differential scanning calorimetry when the heating rate is at and below 20 degrees C/min. For example, at a heating rate of 10 degrees C/min, the two melting peaks occur at 134.8 degrees C and 144.3 degrees C for P1, and 131.1 degrees C and 140.6 degrees C for P2. Through observing the variation of relative intensity of these two melting peaks by changing the heating rate, it was proven that the phenomenon is caused by a melt/recrystallization process. Glass-transition temperature, crystallization temperature and thermal degradation behavior of these co-polymers were also discussed.

A recombinant plasmid was constructed by inserting a DNA fragment with the coding region of Cu/Zn±superoxide dismutase (Cu/Zn±SOD) cDNA from sweet potato, Ipomoea batatas (l) Lam cv Tainong 57, into the 3' end of the open reading frame of the glutathione S-transferase (GST) gene in an expression vector, pGEX-2T. The constructed plasmid was transformed into E coli XL1 Blue. Fusion proteins of Cu/Zn±SOD and GST (GST±SOD) were produced from the recombinant E coli. About 6 mg of GST±SOD fusion proteins could be obtained from 1 dm 3 of cultural broth after induction with 0.075 mmol dm À3 Isopropyl-b-D-thiogalactoside (IPTG). Lactose was not an ef®cient inducer. High cell density culture was performed by fed-batch fermentation using a glucose analyzer to control glucose concentration at 1 g dm À3 . The cell density of the fed-batch culture reached an OD 600 of 30, the total amount of GST±SOD fusion protein was 100 mg dm À3 which is about 14 times more than that of the batch culture. Most of the fusion proteins were shown to be in an active monomeric form, and the molecular weight was estimated to be 45 kDa by SDS±PAGE and 47 kDa by gel ®ltration. The speci®c activity of the puri®ed fusion proteins was about 1200 mg À1 and equal to 3200 unit per mg of SOD domain only.