Comparison of pure cultures and natural assemblages of planktonic photosynthetic sulfur bacteria by low molecular mass RNA fingerprinting

Pure cultures of phototrophic sulfur bacteria were compared to natural popu lations that bloom in karstic lakes by electrophoretic analysis of low mole cular mass RNA molecules (lmwRNA) and microscopy. Similarities between domi nant community members, field isolates and reference strains were establish ed by comparing the lmwRNA band patterns through dendrograms produced with Euclidean distances and the average linkage clustering method, by a single, quick, one-step method. The fingerprinting analysis had three objectives: (i) to compare microbial assemblages from different geographical locations, (ii) to compare those organisms which grow in pure culture to those formin g pranktonic blooms and (iii) to give a preliminary view of the identity of the predominant community members. The ImwRNA analysis yielded a number of clusters consistent with the microscopic observations and allowed rapid co mparison of the microbial communities without the need to isolate their ind ividual components. The fingerprints of natural communities were different from most of the laboratory strains tested. Purple sulfur bacteria responsi ble for the blooms analyzed in karstic lakes were mon closely related to th e Thiocystis group than to the classical strains extensively studied in the laboratory. (C) 2000 Federation of European Microbiological Societies. Pub lished by Elsevier Science B.V. All rights reserved.