AME 23:1-11 (2000)  -  doi:10.3354/ame023001

Genetic diversity of total, active and culturable marine bacteria in coastal seawater

Laetitia Bernard1, Hendrik Schäfer2,*, Fabien Joux1, Claude Courties3, Gerard Muyzer4, Philippe Lebaron1,**

1Observatoire Océanologique, Université Pierre et Marie Curie, UMR-7621 CNRS, Institut National des Sciences de l¹Univers, BP 44, 66651 Banyuls-sur-Mer Cedex, France
2Max-Planck-Institut für Marine Mikrobiologie, 28359 Bremen, Celsiusstr. 1, Germany
3Observatoire Océanologique, Université Pierre et Marie Curie, UMR-7628 CNRS, BP 44, 66651 Banyuls-sur-Mer Cedex, France
4Netherlands Institute for Sea Research, 1790 AB Den Burg, Texel, The Netherlands
*Present address: Netherlands Institute for Sea Research, 1790 AB Den Burg, Texel, The Netherlands **Corresponding author. E-mail: .

ABSTRACT: The genetic diversity of marine bacteria from coastal Mediterranean water was analyzed using denaturing gradient gel electrophoresis (DGGE) and comparative sequence analysis of PCR-amplified 16S rRNA genes. The diversity of the whole bacterial assemblage was compared to the diversity of the fraction of actively respiring bacterial cells and of culturable bacteria. Culturable bacteria were isolated on agar plates using 4 different culture media, as well as in filtered autoclaved seawater following dilution to extinction. The cell fractions exhibited varied genetic diversity. High similarity between DGGE patterns obtained from the whole bacterial assemblage and those obtained from the active cell fraction (representing only 3% of total cells) indicated the simultaneous presence of both active and inactive cells within populations corresponding to numerous bacterial phylotypes defined as DGGE bands. Furthermore, an important source of genetic diversity corresponding to viable organisms, detected by culturability on agar media and in dilution culture with unamended seawater, was not detectable by DGGE patterns obtained from total cells. Most of the strains isolated by dilution cultures were different from those isolated on solid agar media. These results suggest that studies on the structure of complex marine bacterial communities do not necessarily reflect the physiological heterogeneity of ecologically important populations and may ignore populations present at low relative abundance that can play a key ecological role.

KEY WORDS: Activity · Cell sorting · Culturability · Genetic diversity · Marine bacteria · Oligotrophy

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