BIOTECHNOLOGY LETTERS Volume 16 No.9 (Sept.1994) p.903-908 Received as revised 1st July EFFECTS OF INDUCER LEVELS ON A RECOMBINANT BACTERIAL BIOFILM FORMATION AND GENE EXPRESSION CHING-TSAN HUANG 1, STEVEN W. PERETIT 2 AND JAMES D. BRYERS L* 1The Center for Biofilm Engineering, Montana State University Bozeman, Montana 59717, U. S. A. 2Depaml~nt of Chemical Engineering, North Carolina State University Raleigh, North Carolina 27695, U. S. A. SUMMARY A segregationally stable host-plasmid system, E. coil DH5ot (pTKW106), was used to study the effect of induction on the accumulation rate of cells and gene expression in biofilm cultures. Isopropyl l;-D-thiogalactoside (IPTG) was used to induce the expression of B-galactosidase from the plasmid. The biof'drn cell net accumulation rates decreased with increasing induction levels. At 0.17 and 0.34 mM of IPTG, the 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 density~never increased. At 0.17 and 0.34 mM of IPTG, B-galactosidase contents reached maxima 36 hours after induction with both amounts representing about 7.5% of total protein. At 0.51 mM of IPTG, B- galactosidase production reached its maximum, about 16% of total protein, 48 hours after induction. The B-galactosidase mRNA synthesis rates increased with increasing inducer levels. Maximum B-galactosidase mRNA synthesis rates were reached 36 hours after induction for each IPTG concentration. INTRODUCTION Recombinant DNA techniques have been successfully employed in agriculture and in health care, as well as in the commercial production of pharmaceuticals and specialty chemicals. Two impediments to widespread utilization of a recombinant strain are segregational instability of the recombinant plasmid and poor gene expression under different environmental conditions. Numerous studies have reported the many factors affecting gene expression but the majority of studies have been confined to suspended cell cultures (Glick and Whitney, 1987; Bentley et al., 1991; Wood and Peretti, 1991). However, in an open environmental system, the majority of microbial activity is located at interfaces in thin layers known as biofilms. A biofilm is a gelatinous matrix consisting of bacterial cells and their secreted insoluble extracellular polymers. In the past, biofilm research focused on the control of biofilm formation. Recently, the significance of the biofilm mode of bacterial growth in biotechnological applications has received increased attention (Bryers, 1990; Melo et al., 1992). Advantages of using biofilm cultures versus suspended cultures include: ease of biomass-liquid separation, increase of cell concentration, and improvement of over-all system productivity. The combination of 903