Table 1.
Traits characterizing P. difficilis sp. nov. AM-8B5T and previously described Polynucleobacter species
Taxa: 1, AM-8B5T; 2, P. acidiphobus (Hahn et al., 2011b); 3, P. necessarius subsp. asymbioticus (Hahn et al., 2009); 4, P. cosmopolitanus (Hahn et al., 2010); 5, P. rarus (Hahn et al., 2011a). All taxa are non-motile. Note that sufficient phenotypic and chemotaxonomic characterizations are lacking for the obligately endosymbiotic strains of the subspecies P. necessarius subsp. necessarius. −, Negative; +, positive; W, weakly positive; +/−, some strains positive and some strains negative; +/W, some strains positive and some strains weakly positive; W/−, some strains weakly positive and some strains negative.
| Characteristic | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Cell morphology | Short curved rods | Short curved rods | Straight or curved rods | Curved rods | Straight rods |
| Nucleoids visible (DAPI)* | Rarely | Rarely | Rarely | Rarely | Frequently |
| Cell length (μm) | 0.6–1.8 | 0.5–1.4 | 0.5–2.9 | 0.4–1.4 | 0.8–1.8 |
| Cell width (μm) | 0.4–0.5 | 0.4–0.5 | 0.3–0.5 | 0.3–0.5 | 0.6–0.8 |
| Catalase | W | + | + | + | + |
| Oxidase | W | + | + | + | + |
| Growth at: | |||||
| 5 °C | + | − | + | +/− | − |
| 35 °C | − | + | +/− | + | − |
| Maximum NaCl tolerance (%, w/v)† | 0.2 (W) | 0.3 | 0.3–0.5 | 0.3–0.5 | 0.3 (W) |
| Anaerobic growth on: | |||||
| NSY medium | − | + | +/− | +/− | − |
| NSY+0.8 mM nitrate | W | + | + | + | + |
| Growth in mineral medium with acetic acid and B12 | − | W | W/− | W/− | W |
| Assimilation of: | |||||
| Formic acid | W | − | W/− | − | − |
| Glyoxylic acid | − | − | W/− | W/− | + |
| Glycolic acid | − | − | − | − | W |
| Acetic acid | − | W | + | + | + |
| Oxalic acid | − | − | − | − | W |
| Propionic acid | − | − | +/− | +/W | − |
| Pyruvic acid | + | + | + | + | + |
| Malonic acid | − | W | +/− | +/− | − |
| Oxaloacetic acid | W | + | +/− | + | − |
| Malic acid | W | W | +/W | + | + |
| Succinic acid | + | W | + | + | + |
| Fumaric acid | W | − | +/W | + | + |
| Levulinic acid | − | − | W/− | W/− | + |
| Citric acid | − | − | − | +/− | − |
| d-Mannose | − | − | W/− | W/− | W |
| d-Glucose | − | W | W/− | W/− | − |
| d-Galacturonic acid | W | − | W | +/W | + |
| d-Galactose | − | − | W/− | W | − |
| d-Lyxose | W | − | W/− | − | W |
| d-Fructose | − | − | W/− | − | W |
| d-Fucose | W | − | W/− | − | W |
| d-Sorbitol | − | − | W/− | − | − |
| l-Glutamate | − | − | +/− | W/− | − |
| l-Aspartate | − | − | +/− | − | − |
| l-Cysteine | + | + | +/W | + | W |
| l-Alanine | − | − | W/− | +/W | − |
| l-Serine | − | − | − | − | − |
| l-Asparagine | − | − | W/− | − | − |
| Betaine | − | − | W/− | − | − |
| DNA G+C content (mol%) | 49.4 | 48.3 | 44–46 | 44.9 | 40.3 |
DAPI, 4′,6-diamidino-2-phenylindole.
Highest NaCl concentration (added to NSY medium) at which growth was observed.