Generation of a reproducible nutrient-depleted biofilm of Escherichia coli and Burkholderia cepacia

An in vitro method of growing bacteria as a defined nutrient-depleted biofilm is proposed. The medium was defined nutritionally in terms of the quantitative composition and by the total amount of nutrient required to achieve a defined population size. Escherichia coli and Burkholderia cepacia were incubated on a filter support placed on a defined volume of solid medium. The change of biomass of the biofilm population was compared with the change in a planktonic culture. The size of the population in stationary phase was proportional to the concentration of limiting substrate up to 40 mu mol cm(-2) glucose for E. coli and up to 2.7 x 10(-9) mol cm(-2) iron for B. cepacia. Escherichia coli growing exponentially had a growth rate of mu = 0 30 h(-1) in a biofilm and mu = 0.96 h(-1) in planktonic culture. The growth rate, mu, for exponentially growing B. cepacia in a biofilm was 1.12 h(-1) and in planktonic culture 0.78 h(-1). This method allows the limitation of the size of a biofilm population to a chosen value.