The Use of Polystyrene Beads to Prepare Arrayed Samples of Bacillus thuringiensis for Microscopic Examination

A common activity in the global search for useful Cry toxins is the microscopic screening of bacterial colonies for the presence of Bacillus thuringiensis. High-throughput screens require that aliquots from large numbers of colonies be arrayed on a microscopic slide. However, precisely placing a small amount of bacteria on a slide, and at a density that is useful for microscopic examination, is both difficult to achieve and time consuming. Herein we share a simple technique that utilizes a hooked wand and small polystyrene beads to quickly collect, and uniformly apply, aliquots of bacterial colonies onto gridded microscope slides in a manner optimal for viewing. If desired, libraries of examined bacteria can simultaneously be generated by discharging the beads into indexed multiwell plates. This simple and inexpensive method is robust, suitable for both light and phase contrast microscopy, and has been also used successfully to screen randomly mutated bacteria for phenotypic changes.