Evolution, Population Genetics and Genomic Analysis of Marine Microbes:
a Molecular Biologist Does Oceanography

Ena Urbach

            Marine bacteria and archaea  have large populations and are ubiquitous in the  oceans.  They are likely to play important roles in global biogeochemical processes.  Using molecular approaches, microbial ecologists have characterized the phylogenetic diversity of marine microbes.  About a dozen dominant evolutionary groups have been identified, only two of which are currently culturable.  In my past work, I have characterized the evolution and population genetics of one such culturable microbe, Prochlorococcus.  Global Prochlorococcus populations show high genetic variability and a vertical mode of evolutionary inheritance.  I am currently studying the other cultivable group, the Roseobacter cluster.  Roseobacter isolates also exhibit high genetic variability, but Roseobacter sub lineages may evolve new traits by horizontal transfer of DNA from other microbial groups. 

            Genomic approaches promise to yield information about the biochemical potential of environmental microbes.  However, the complexity of natural populations complicates genomic analysis of uncultured organisms.  I am devising methods for genomic analysis of microbes in the sea, using in situ hybridization and flow cytometric cell sorting to obtain  substrates for genomic clone libraries.  An important consideration is the phylogenetic breadth that will yield genetically near-homogeneous materials.  Genomic analysis, population genetics nd evolutionary considerations will all contribute to understanding the activities of marine microbes.