In the bacterial cell, carbon substrates are metabolized by
many different pathways. The three most-studied metabolic
pathways are shown in Fig. 6. Sugars such as glucose
and fructose are mostly processed via pathway I,
yielding PHB homopolymer. If fatty acids or sugars are
metabolized by pathway II, III or other pathways, copolymers
are produced (Aldor and Keasling 2003; Steinbu¨chel
and Lu¨tke-Eversloh 2003).