The results of biotransformation of grease with dry cells of all
recombinant E. coli strains were summarized in Table 1. The FAME
yield at 48 h was only 33% for E. coli (Calb), which is however
slightly higher than that achieved with wet cells (29% at 48 h).
Similarly, dry cells of E. coli (Tll) gave 81% yield of FAME, while
the corresponding wet cells afforded 74% yield. The combination
of the dry cells of E. coli (Calb) + E. coli (Tll) at a ratio of 2:8 as tandem
lipases gave only silighly higher FAME yield than the use of
the dry cells of E. Coli (Tll) alone (82% vs 81%). This is also silimar
to the case of using wet cells. The best tandem lipases system for
the production of biodisel from grease is the dry cells of E.coli
(Calb/Tll), which gave a FAME yield of 93% at 48 h, and 95% at
72 h. The better performance of the recombinant E. coli cells coexpressing
tandem lipases than the combination of the cells of
E. coli (Calb) and E. coli (Tll) may be due to the reduced mass transfer
problem of the substrate crossing the cell membranes. While
the E. coli (Calb) + E. coli (Tll) system requires the substrate crossing
membranes of two microorganisms for tandem catalysis, in E. coli
(Calb/Tll) system the substrate needs to cross the membrane of
only one microorganism for tandem catalysis.
For whole-cell catalyzed FAME production, the mass transfer of