Growth of micro-organisms in gel-stabilized two-dimensional diffusion gradient systems

The Szybalski wedge plate technique was modified to generate two-dimensional diffusion gradients for two environmental variables: pH value and NaCl concentration were selected in this study. After experimentation, pH values chosen ranged from 3.9 to 8.1 and salt concentrations from 23 to 79 g 1(-1). The pH gradients were slightly sigmoidal whilst the salt gradients were approximately linear. The reproducibility of the technique was assessed and found to be satisfactory in replicate growth experiments. A wide range of growth patterns was observed for a large variety of different bacterial types. The growth boundary and the pattern details are sufficiently distinct to suggest that the technique can distinguish between closely related species or strains.