Polyhydroxyalcanoates (PHA) are a class of naturally occurring polyesters that are synthe­sized by various microorganisms as a reserve material for carbon and energy. When the bacteria are grown under low nutrition conditions, PHAs accumulate in the cytoplasm of the bacteria as hydrophobic granules and act as a carbon reservoir as well as an electron sink. Since these polymers are biodegradable and also biocompatible, they are of high demand in the pharmaceutical, fiber, and horticulture industries. In Ralstonia eutropha and most other PHA accumulating bacteria, polyhydroxybutyrate (PHB) is synthesized from acetyl — CoA through three enzymes: (1) P-ketothiolase, which condenses two molecules of acetyl-CoA to P-acetoacetyl-CoA, (2) an NADPH-dependent acetoacetyl-CoA reductase that catalyzes the formation of D-(2)-3-hydroxybutyryl-CoA (3HB-CoA), and (3) PHA synthase, which polym­erizes 3HB-CoA to PHB (Schubert et al. 1988; Slater et al. 19882 . Currently, industrial synthesis of PHAs involves aerobic processes that are energy intensive. There is a need, therefore, to develop newer fermentative ways of synthesizing these compounds. When Methylobacterium rhodesianum MJ 126-J and R. eutropha DSM11348 were cultured in a medium containing crude glycerol and casein hydrolysates, the amount of PHB produced was 50g/L and the net conversion of glycerol to PHB was 17% (Bormann and Roth 1999). E. coli has also been engineered to produce PHBs by mutating the arcA2 locus. The ArcAB system of E. coli represses genes that encode the enzymes involved in aerobic respiration, such as those of the tricarboxylic acid cycle, under anaerobic and microaerobic conditions (Salmon et al. 2005). The mutation in arcA region would elevate the tricarboxylic acid cycle activity, which supplies large amounts of reducing equivalents such as NADH and NADPH. Excess reducing equivalents favor the formation of an electron sink like PHBs (Nikel et al. 2006). The recombinant E. coli with mutation in arcA produced 1.44g/L ofPHBs in glucose media while the corresponding non-mutant produced only 0.07 g/L of PHBs. When recom­binant E. coli was used for the fermentation of glycerol, the amount of PHBs accumulated in the fermentation reactor was 1.47 times higher than that produced when glucose was the carbon source (Nikel et al. 2008). The difference in PHB concentrations was attributed to the difference in redox characteristics of glucose and glycerol carbon sources (Nikel et al. 2008).