Microgradients in bacterial colonies: use of fluorescence ratio imaging, anon-invasive technique.

Fluorescence ratio imaging is a non-invasive technique for studying the for mation of microgradients in immobilised bacterial colonies. These gradients can be quantified easily when combined with the gel cassette system design ed at the Institute of Food Research, Norwich, UK. Colonies of Lactobacillu s curvatus were observed using this technique and relevant pH gradients wer e present when the colonies reached a diameter of about 100 mu m. These pH gradients were due to production of lactic acid by L. curvatus cells in the colonies. The spatial resolution of the images was about 1.5 mu m (scale o f bacterial cells) and therefore very suitable for observing local effects in colonies which ranged in sizes From 1 to 500 mu m. (C) 2000 Elsevier Sci ence B.V. All rights reserved.