AME 13:63-74 (1997)  -  doi:10.3354/ame013063

The genetic structure of a Shewanella putrefaciens population, the dominant culturable denitrifier in the low oxygen and anoxic water of the central Baltic, was investigated using Randomly Amplified Polymorphic DNA (RAPD) genotyping. Five different procedures were used for the isolation of strains from 2 depth profiles in the Gotland Deep, sampled during 2 consecutive summers (1986 and 1987). The conditions in the water column were comparable for both sampling periods, i.e. the water column was stratified and characterized by pronounced chemical gradients in both years. A total of 59 S. putrefaciens isolates were obtained in 1986 and 54 S. putrefaciens strains in 1987. Identification of the isolates, to the species level, was carried out using low-molecular-weight (LMW) RNA profiling. RAPD fingerprinting, using 3 random decamer primers, enabled the detection of subpopulations within the S. putrefaciens population. Thirteen different RAPD genotypes were defined, based upon Neighbor Joining (NJ) and unweighted pair group method using arithmetic averages (UPGMA) clustering. The range of RAPD genotypes varied with the isolation procedures, indicating different bacterial clones with different physiological traits within the population, i.e. specific clones were obtained with specific isolation procedures. Thus, the isolation procedure is not merely selective at the species level, but at the clonal level of a given species as well. The striking observation was that all strains isolated in 1987 clustered with RAPD genotypes already found in 1986. This is interpreted as stability over time of the genetic structure of the S. putrefaciens population in the water column of the central Baltic.

RAPD · Shewanella putrefaciens · Diversity · Baltic Sea · Population structure · Bacterial clones · Stability · Denitrifier