HETEROTROPHIC BACTERIA, ACTIVITY AND BACTERIAL DIVERSITY IN 2 COASTALLAGOONS AS DETECTED BY CULTURE AND 16S RIBOSOMAL-RNA GENES PCR AMPLIFICATION AND PARTIAL SEQUENCING

Activity and numbers of heterotrophic bacteria have indicated that, as expected, Prevost Lagoon is more eutrophic than Arcachon Bay. Amplifi cation and sequence analysis of the 16S rRNA genes from DNA samples ex tracted directly from the environment allow the determination of phylo genetic relationships among members of microbial communities in natura l ecosystems without the need for cultivation. Analysis of partial 16S rRNA gene sequences obtained from Stations A and 11 revealed that, in both environments, a relatively large number of clones related to Cyt ophaga/Flexibacter/Bacteroides as well as to alpha-Proteobacteria were found. One hundred percent similarity with the sequences of the data bases were not found for any of the more than a hundred clones studied . In fact for most clones maximum similarity was below 95% for the nuc leotide series sequenced. Similarity was not higher with any of the se quences found for the 14 isolates (pure cultures) obtained from the sa me samples. Redundancy, i.e. number of identical sequences, was higher in the samples from Arcachon. In addition, sequences related to repre sentatives of ten major phylogenetic branches of Eubacteria were obtai ned from Prevost Lagoon, however only five branches were represented b y the data from Arcachon. These findings indicate a higher bacterial d iversity in Prevost Lagoon.