Identification of complex composition, strong strain diversity and directional selection in local Pseudomonas stutzeri populations from marine sediment and soils.

Members of Pseudomonas stutzeri have been isolated world-wide from various habitats including aquatic and terrestrial ecosystems. The global population has a clonal structure, is of exceptionally high genetic diversity and has been grouped into eight genomovars. We have analysed four local populations (n = 89-125) from three geographically separated habitats (two from a marine sediment and two from different soils) by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR), restriction fragment length polymorphism (RFLP) of the rpoB gene and 16S rDNA sequences in order to quantify the influence of evolutionary forces on closely related groups of proliferating cells in situ. All populations consisted of a complex structure of genomic subgroups with variable numbers of members. The analyses revealed that the two populations from marine sediment were rather similar. At least three of the populations were influenced by migrational input as concluded from the presence of members from different genomovars. All populations showed very high strain diversity suggesting strong influence of mutability. Neutrality tests indicated that two or possibly three of the populations were shaped by directional selection. Thus, the local populations of P. stutzeri reflect already the high genetic diversity of the global population and are influenced, to different extents, by migration, mutation and directional selection.