EFFECTS OF INDUCER LEVELS ON A RECOMBINANT BACTERIAL BIOFILM FORMATION AND GENE-EXPRESSION

A segregationally stable host-plasmid system, E. coli DH5 alpha (pTKW1 06), was used to study the effect of induction on the accumulation rat e of cells and gene expression in biofilm cultures. Isopropyl beta-D-t hiogalactoside (IPTG) was used to induce the expression of beta-galact osidase from the plasmid. The biofilm cell net accumulation rates decr eased with increasing induction levels. At 0.17 and 0.34 mM of IPTG, t he biofilm cell net accumulation rates ranged between 17 and 30% when compared to the uninduced case. At 0.51 mM of IPTG, the biofilm cell d ensity never increased. At 0.17 and 0.34 mM of IPTG, beta-galactosidas e contents reached maxima 36 hours after induction with both amounts r epresenting about 7.5% of total protein. At 0.51 mM of IPTG, beta-gata ctosidase production reached its maximum, about 16% of total protein, 48 hours after induction. The beta-galactosidase mRNA synthesis rates increased with increasing inducer levels. Maximum beta-galactosidase m RNA synthesis rates were reached 36 hours after induction for each IPT G concentration.