2.3. Preparation of recombinant E. coli cells as biocatalysts for
biodiesel production from grease
Two milliliters overnight inoculum of the above constructed recombinant
E. coli strain [E. coli (Calb), E. coli (Tll), E. coli (Calb/Tll), or
E. coli (Calb-Tll)] was added to 100 mL LB medium supplemented
with 50 mg/L of kanamycin in a 500 mL Erlenmeyer flask. The culture
was incubated at 37 C and 250 rpm to reach an OD600nm of
0.6. Subsequently, lipase expression was induced by the addition
of isopropylthiogalactoside (IPTG) to a concentration 0.2 mM. The
culture was grown for another 4 h at 30 C and 250 rpm to OD600nm
of 3.0, and the cells were harvested by centrifugation at 3440 g for
5 min. Washing with water followed by centrifugation gave the
cell pallets as wet-cell biocatalysts. To prepare dry-cell biocatalysts,
the wet cells were lyophilized to remove water.
The expressing of the corresponding lipase was analyzed by
sodium dodecyl sulfate–polyacrylamide gel electrophoresis
(SDS–PAGE). Cell-free extract was prepared by the disruption of
the harvested cells with homogenizer under 20 psi followed by
centrifugation. Soluble cell lysate (corresponding to 0.5 mL cell
culture) were loaded to SDS–PAGE, and the gels were stained with
Coomassie brilliant blue.
2.4. Specific activity of the recombinant E. coli cells for the hydrolys