nd nd not thiocyanate, and uses ammonium salts or nitrates as nitrogen source. Obligately chemolithotrophic and auto-trophic. Strict aerobe. Optimum temperature for growth: 28-32°C; growth range: 8-39°C. Optimum pH for growth: 6.5-6.9; growth range pH: 4.5-8.5. Isolated from seawater, canal water, and corroding concrete. Frequently, this organism is found in marine mud and in seawater. Presumably widely distributed in freshwater, soil, and marine environments. Member of the Gammaproteobacteria.

Type strain: ATCC 23641, DSM 15147, NCIB 8539.

GenBank accession number (16S rRNA): AF173169.

2. Halothiobacillus halophilus (Wood and Kelly 1991) Kelly and Wood 2000, 515VP (Thiobacillus halophilus Wood and Kelly 1991, 280.) L. n. halophil salt-loving; M.L. adj. halophilus loving salt.

Cells are Gram-negative small rods. Obligately halo-philic, optimum growth with 1 M NaCl and tolerating up to 4 M NaCl. Obligately chemolithoautotrophic; grows aero-bically with thiosulfate, tetrathionate or sulfur; lowers the pH to 5.5-6. Also oxidizes sulfide, trithionate, and hexath-ionate. On thiosulfate agar, colonies are small (1-3 mm), circular, opaque, smooth, and convex, and become yellow/ white with deposited sulfur. Optimum temperature for growth 30-32°C and optimum pH for growth 7.0-7.3. Nitrate reduced to nitrite but anaerobic growth with thiosulfate does not occur. Contains ubiquinone Q-8. Isolated from a salt lake in the wheat belt of Western Australia. Member of the Gammaproteobacteria.

Type strain: DSM 6132, ATCC 49870.

GenBank accession number (16S rRNA): U58020.

3. Halothiobacillus hydrothermalis (Durand, Reysenbach, Prieur and Pace 1993) Kelly and Wood 2000, 515VP (Thiobacillus hydrothermalis Durand, Reysenbach, Prieur and Pace 1993, 43.)

hy.dro.ther.malis. M.L. hydrothermalis pertaining to a hydrothermal vent in the North Fiji basin.

Cells are Gram negative, motile, nonsporeforming, short rods, 0.5 X 1.0 |im. Obligately chemolithotrophic, using oxidation of thiosulfate, tetrathionate, sulfide, or sulfur for growth. Lowers the pH of thiosulfate medium to 4.8, without formation of tetrathionate. Growth occurs in the ranges pH 6-9, 11-45°C, and 0-2 M NaCl; no growth at pH 5 or 9.5, or at 8°C or 50°C. Optimum pH 7.5-8 and temperature 35-40°C; optimum salinity 0.43 M NaCl, tolerates 2 M NaCl. Contains ubiquinone Q-8. Isolated from samples taken from a depth of 2 km in an active hydrothermal vent in a rift system of the North Fiji Basin. Member of the Gammapro-teobacteria.

The mol% G + C of the DNA is: 67.1-67.4 (TM Bd, HPLC).

Type strain: ATCC 51453, DSM 7121.

GenBank accession number (16S rRNA): M90662.

4. Halothiobacillus kellyi Sievert, Heidorn and Kuever 2000, 1235VP

kel'ly.i. M.L. gen. n. kellyi of Kelly; named after Donovan P. Kelly, a British microbiologist who has made important contributions to research on sulfur-oxidizing bacteria and their physiology.

Cells are Gram negative, motile, and rod shaped (0.40.6 X 1.2-2.5 |m). The organism is strictly aerobic and grows autotrophically on thiosulfate, tetrathionate, sulfur, and sulfide, but not thiocyanate. The organism does not grow heterotrophically. When thiosulfate is used as the primary energy source, a transient formation of sulfur occurs. During growth on reduced sulfur compounds, the pH decreases from neutrality to around pH 2.8. Thiosulfate is completely oxidized to sulfate. Autotrophic growth on thiosulfate occurs between pH 3.5 and 8.5 and at a temperature of 35-49°C; optimum growth occurs at pH 6.5 and at 37-42°C. The optimal NaCl concentration for growth is 0.40.5 M; growth is possible between NaCl concentrations of 0-2 M. Nitrate is not used as terminal electron acceptor. The average maximum specific growth rate on thiosulfate is 0.45 h—1 for the type strain, Milos-BIII1. On thiosulfate agar, cells produce white to yellowish, smooth, entire colonies (diameter on 1.2% w/v agar is 1-4 mm), in which sulfur is deposited and acid is produced. Ubiquinone Q-8 is present in the respiratory chain. As determined by 16S rRNA gene sequence analysis, Halothiobacillus kellyi belongs to the Gammaproteobacteria and is most closely related to other members of the Halothiobacillus genus. The type strain Milos-BIII1 was isolated from a marine, shallow-water, hydrothermal vent system and is deposited at the DSM.

Type strain: Milos-BIII, DSM 13162.

GenBank accession number (16S rRNA): AF170419.

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