DIFFERENTIATION OF SHEWANELLA-PUTREFACIENS AND SHEWANELLA-ALGA ON THEBASIS OF WHOLE-CELL PROTEIN PROFILES, RIBOTYPING, PHENOTYPIC CHARACTERIZATION, AND 16S RIBOSOMAL-RNA GENE SEQUENCE-ANALYSIS

Seventy-six presumed Shewanella putrefaciens isolates from fish, oil d rillings, and clinical specimens, the type strain of Shewanella putref aciens (ATCC 8071), the type strain of Shewanella alga (IAM 14159), an d the type strain of Shewanella hanedai (ATCC 33224) were compared by several typing methods. Numerical analysis of sodium dodecyl sulfate-p olyacrylamide gel electrophoresis of whole-cell protein and ribotyping patterns showed that the strains were separated into two distinct clu sters with 56% +/- 10% and 40% +/- 14% similarity for whole-cell prote in profiling and ribotyping, respectively. One cluster consisted of 26 isolates with 52 to 55 mol% G + C and included 15 human isolates, mos tly clinical specimens, 8 isolates from marine waters, and the type st rain of S. alga. This homogeneous cluster of mesophilic, halotolerant strains was by all analyses identical to the recently defined species S. alga (U. Simidu et at., Int. J. Syst. Bacteriol. 40:331-336, 1990). Fifty-two typically psychrotolerant strains formed the other, more he terogeneous major cluster, with 43 to 47 mol% G + C. The type strain o f S. putrefaciens was included in this group. The two groups were conf irmed by 16S rRNA gene sequence analysis. It is concluded that the iso lates must be considered two different species, S. alga and S. putrefa ciens, and that most mesophilic isolates formerly identified as S. put refaciens belong to S. alga. The ecological role and potential pathoge nicity of S. alga can be evaluated only if the organism is correctly i dentified.