In A. eutrophus two acetyl-CoA moieties are
condensed to acetoacetyl-CoA by P-ketothiolase. An
NADPH-dependent reductase reduces acetoacetyl-CoA to
D( - )-3-hydroxybutyryl-CoA, which is then linked to the
growing chain of P(3HB) by the PHA ~ynthase.~~T"h' e
PHA biosynthetic route together with degradation pathway
in A. eutrophus is shown in Figure 2. PHA synthesis in
Rhodospirillum rubrum is similar to A. eutrophus with minor
modifications in the second step. The acetoacetyl-CoA
is reduced by an NADH-dependent reductase to L( +)-3-
hydroxybutyryl-CoA, which is then converted to D( -)-3-
hydroxybutyryl-CoA by two enoyl-CoA hydratases. ' 17,''*
P. oleovorans and most pseudomonads belonging to the
rRNA homology group I synthesize MCL-PHA from various
MCL-alkanes, alkanols, or a l k a n ~ a t e s .I~t w~a,s~ s~ug -
gested that the 3-hydroxyacyl-CoA intermediates of the
P-oxidation pathway are channeled to PHA synthesis.92
This is referred to as the P. oleovorans PHA biosynthetic
pathway. Most pseudomonads belonging to rEWA homology
group I except P. oleovorans also synthesize MCLPHAs
from acetyl-CoA via fatty-acid biosynthetic pathway
,593663169w hich is referred to as the Pseudomonas
aeruginosa PHA biosynthetic pathway.