Microbial community dynamics in Mediterranean nutrient-enriched seawater mesocosms: changes in the genetic diversity of bacterial populations

A mesocosm experiment was pel formed to study the influence of nutrients on activity and diversity of bacterial assemblages from the Mediterranean Sea . Changes in the diversity of the predominant bacterial populations were mo nitored by DGGE fingerprinting of PCR products derived from 16S rRNA encodi ng genes. Fluctuations in the diversity of the most active populations was inferred by performing the DGGE fingerprinting on the basis of the cellular rRNA after reverse transcription and PCR amplification. DNA-derived DGGE p atterns obtained from duplicate control and nutrient-enriched. mesocosms sh owed differences in the development of the bacterial communities between co ntrol and nutrient-enriched experimental mesocosms. Multidimensional scalin g analysis of the DNA-derived DGGE fingerprints indicated that duplicate tr eatments were reproducible. DNA- and RNA-derived DGGE fingerprints of bacte rial assemblages changed over time, showing that the composition of the bac terial assemblages, as well as the most active bacterial populations change d during, different phases of the incubation. Sequences of predominant DGGE bands in RNA-derived patterns were similar to 16S rRNA gene sequences of m embers of the alpha-, gamma- and delta -Proteobacteria and of the Cytophaga -Flavobacterium-Bacteriodes phylum (CFB). Bands corresponding to Ruegeria-l ike bacteria and members of the CFB became especially dominant during the c ourse of incubation, suggesting that these populations were important contr ibutors to bacterial production and activity in the post-grazing phase of t he experiment. (C) 2001 Federation of European Microbiological Societies. p ublished by Elsevier Science B.V. All rights reserved.