Characterization of Azotobacter vinelandii aggregation in submerged culture by digital image analysis

A simple and accurate method for determining the distribution of sizes of single cells and aggregates of Azotobacter vinelandii by image analysis has been developed. A staining procedure using methylene blue helps to enhance the contrast between aggregates and background with out altering aggregate size distribution. Sample dilution affected the distribution of the Population and therefore should be avoided. Mixing and aeration conditions during culture play an important role in the aggregation of A. vinelandii. Cells grown under mild mixing conditions (unbaffled flasks) presented a thick slime layer and formed aggregates of up to 35 pm of average equivalent diameter. In contrast, under strong agitation conditions (baffled flasks) practically no aggregates were formed throught cultivation. The method described can be used for the characterization of aggregation of other microbial Cultures. (C) 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.