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Microgradients in bacterial colonies : use of fluorescence ratio imaging : a non-invasive technique

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Author: Malakar, P.K. · Brocklehurst, T.F. · Mackie, A.R. · Wilson, P.D.G. · Zwietering, M.H. · Riet, K. van 't
Institution: Centraal Instituut voor Voedingsonderzoek TNO
Source:International Journal of Food Microbiology, 1, 56, 71-80
Identifier: 71910
doi: doi:10.1016/S0168-1605(00)00222-1
Keywords: Nutrition · Bacterial growth · Bacterium colony · Calibration · Cell density · Fluorescence · Image analysis · Immobilized cell · Lactobacillus curvatus · Technique · Bacteriological Techniques · Hydrogen-Ion Concentration · Image Processing, Computer-Assisted · Lactobacillus · Microscopy, Fluorescence


Fluorescence ratio imaging is a non-invasive technique for studying the formation of microgradients in immobilised bacterial colonies. These gradients can be quantified easily when combined with the gel cassette system designed at the Institute of Food Research, Norwich, UK. Colonies of Lactobacillus curvatus were observed using this technique and relevant pH gradients were present when the colonies reached a diameter of about 100 μm. 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 μm (scale of bacterial cells) and therefore very suitable for observing local effects in colonies which ranged in sizes from 1 to 500 μm. Copyright (C) 2000 Elsevier Science B.V.