BACTERIAL DIVERSITY IN 2 COASTAL LAGOONS DEDUCED FROM 16S RDNA PCR AMPLIFICATION AND PARTIAL SEQUENCING

Amplification and sequence analysis of the 16S rRNA genes from DNA sam ples extracted directly from the environment allows the study of micro bial diversity in natural ecosystems without the need for cultivation. In this study this methodology has been applied to two coastal lagoon s. Activity and numbers of heterotrophic bacteria have indicated that, as expected, Prevost lagoon (located on the French Mediterranean coas t) is more eutrophic than that of the Arcachon Bay (French Atlantic co ast). Analysis of partial 16S rRNA gene sequences revealed that, in bo th environments, a relatively large number of clones related to Cytoph aga/Flexibacter/Bacteroides as well as to alpha-Proteobacteria in 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 app rox. 200 bases 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 Bacteria were obtaine d from Prevost lagoon; however only five branches were represented by the data from Arcachon. These findings indicated a higher bacterial ph ylogenetic diversity in the Prevost lagoon.