The Genus Spirillum: a Taxonomic Study

The morphological, physiological, and nutritional characteristics and the deoxyribonucleic acid (DNA) base compositions of 39 strains of Spirillum (including the available type strains) were determined. A uniform methodology provided a basis for comparison of the strains. The results, together with previous serological data and with previous results for two strains of Spirillum volutans, indicate that the present genus Spirillum should be divided into three genera, with the original name being restricted to obligately microaerophilic freshwater forms having a large cell diameter and a DNA base composition of 36 to 38 mol % guanine + cytosine (G + C). This genus would contain at present only one species, the type species, S. volutans. The generic name Aquaspirillum is proposed for the aerobic, freshwater forms having a DNA base composition of 49 to 65 mol % G + C. Thirteen species are included in this genus: the type species A. serpens (Müller) comb. nov.; A. metamorphum (Terasaki) comb. nov.; A. putridiconchylium (Terasaki) comb. nov.; A. sinuosum (Williams and Rittenberg) comb. nov.; A. gracile (Canale-Parola et al.) comb. nov.; A. itersonii (Giesberger) comb. nov.; A. dispar sp. nov.; A. polymorphum (Williams and Rittenberg) comb. nov.; A. aquaticum sp. nov.; A. delicatum (Leifson) comb. nov.; A. peregrinum (Pretorius) comb. nov.; A. anulus (Williams and Rittenberg) comb. nov.; and A. giesbergeri (Williams and Rittenberg) comb. nov. Strains of the latter two species, plus an additional strain (ATCC 12289), appear to be related to one another but should not be included together in a single species without additional supporting evidence (e.g., DNA homology studies). The following are proposed as type or neotype strains: A. serpens ATCC 12638 (neotype); A. metamorphum ATCC 15280 (type); A. putridiconchylium ATCC 15279 (type); A. gracile ATCC 19624 (type); A. itersonii ATCC 12639 (neotype); A. dispar ATCC 27510 (type); and A. aquaticum ATCC 11330 (type). The generic name Oceanospirillum is proposed for marine forms which do not attack carbohydrates and which possess a DNA base composition of 42 to 48 mol % G + C; five species are included. These are as follows: the type species O. linum (Williams and Rittenberg) comb. nov.; O. minutulum (Watanabe) comb. nov.; O. beijerinckii (Williams and Rittenberg) comb. nov.; O. japonicum (Watanabe) comb. nov.; and O. maris sp. nov. The following are proposed as type or neotype strains: O. minutulum ATCC 19192 (neotype); O. japonicum ATCC 19191 (neotype); and O. maris ATCC 27509 (type).