aUnder carbon dioxide limitation.

bGrows mixotrophically with tetrathionate plus glucose or yeast extract.

aUnder carbon dioxide limitation.

bGrows mixotrophically with tetrathionate plus glucose or yeast extract.

strain (ATCC 33020) was not taxonomically related to the others (Selenska-Pobell et al., 1998). It is, therefore, inevitable that some strains assigned to Acidithiobacillus ferrooxidans will in due course be reassigned to new species or genera.

Thiobacillus concretivorus (Parker, 1945) was once listed as a distinct species in Bergey's Manual (Parker, 1957) and appeared in the Approved Lists of Bacterial Names (Skerman et al., 1980). It is, however, now recognized as a synonym of T. thiooxidans (now Acidithiobacillus thiooxidans) (Vishniac, 1974; Kelly and Harrison, 1989).

List of species of the genus Acidithiobacillus

1. Acidithiobacillus thiooxidans (Waksman and Joffe 1922) Kelly and Wood 2000, 513VP (Thiobacillus thiooxidansWaks-man and Joffe 1922, 239.)

thio.ox' i.dans. Gr. n. thios sulfur; M.L. v. oxido make acid, oxidize; M.L. part adj. thiooxidans oxidizing sulfur.

Short rods, single, paired or in short chains, 0.5 X 1.02.0 |im. Motile by means of a polar flagellum (Doetsch et al., 1967). Minute colonies (0.5-1.0 mm) grown on thio-sulfate agar appear transparent or whitish yellow and clear on prolonged incubation; edges appear complete. This organism grows in liquid medium on S0, thiosulfate, or tetrathionate. Tetrathionate and sulfur may be produced transiently during growth on thiosulfate. This organism cannot oxidize iron or pyrite but has been shown to grow on sulfur from pyrite in co-culture with "Leptospirillum ferrooxidans", an iron-oxidizing, non-sulfur-oxidizing vibrio. Reduces pH of sulfur media to values of 0.5-0.8.

Obligate chemolithotroph and autotroph; remarkable ability to oxidize S0 rapidly. Strictly aerobic. Ammonium sulfate used as nitrogen source. Optimum temperature: 28-30°C; temperature range: 10-37°C. Optimum pH: 2.0-3.0; growth range pH: 0.5-5.5. Isolated from soil, sulfur springs, acid mine drainage waters, and corroding concrete and steel environments. Likely to be widely distributed in acidic habitats with elemental sulfur or soluble reduced sulfur compounds. Member of the Gammaproteobacteria.

Type strain: ATCC 19377, NCIMB 8343.

GenBank accession number (16S rRNA): Y11596.

2. Acidithiobacillus albertensis (Bryant, McGroarty, Costerton and Laishley 1988) Kelly and Wood 2000, 514VP (Thwbaallus albertis Bryant, McGroarty, Costerton and Laishley 1988, 221.)

al.ber'ten.sis. M.L. adj. albertensis named for Alberta, Canadian province of Alberta.

Rods, 0.45 X 1.2-1.5 |im. Motile by means of a tuft of polar flagella. Condensed glycocalyx present, extending outwards from outer membrane, apparently involved in cell adhesion to surfaces such as sulfur. This organism grows on sulfur, thiosulfate, or tetrathionate; tetrathionate is accumulated transiently during growth on thiosulfate but not on sulfur. Intracellular sulfur granules have been observed in stationary phase cells. Obligate chemolithotroph and autotroph. Aerobic. Ammonium sulfate is used as nitrogen source. Optimum temperature: 28-30°C. Optimum pH: 3.5-4.0; growth range pH: 2.0-4.5. Isolated from extremely acidic soil adjacent to a sulfur stockpile. Probably occurs in other similar environments.

Type strain: ATCC 35403.

3. Acidithiobacillus caldus (Hallberg and Lindstrom 1995) Kelly and Wood 2000, 514VP (Thiobacillus caldus Hallberg and Lindstrom 1995, 619.) caldus. M.L. adj. caldus warm, liking warmth.

Cells are short, motile, Gram-negative rods, 0.7-0.8 X 1.2-1.8 | m. Capable of chemolithoautotrophic growth with thiosulfate, tetrathionate, sulfide, sulfur, and molecular hydrogen; no growth with ferrous iron or sulfidic ores. Mix-otrophic growth with tetrathionate and glucose or yeast extract. Colonies on tetrathionate agar are small, circular, convex, smooth, and transparent, with precipitated sulfur in their center. Growth occurs between 32 and 52°C and pH 1-3.5, with optimum growth at 45°C and pH 2-2.5. Contains ubiquinone Q-8 and a menaquinone. No significant DNA hybridization (2-20%) with T. ferrooxidans, T. thio-oxidans, T. cuprinus, or T. thioparus. Member of the Gam-maproteobacteria.

Type strain: KU, ATCC 51756, DSM 8584.

GenBank accession number (16S rRNA): Z29975.

4. Acidithiobacillus ferrooxidans (Temple and Colmer 1951) Kelly and Wood 2000, 513VP (Thiobacillus ferrooxidans Temple and Colmer 1951, 605.)

ferro.ox'i.dans. L. n. ferrum iron; M.L. v. oxido oxidize, make acid; M.L. part. adj. ferrooxidans iron-oxidizing.

Rods, usually single or in pairs, 0.5 X 1.0 |im. Motile; the type strain is motile by a single polar flagellum. Small colonies (0.5-1 mm) grown on thiosulfate or tetrathionate agar are round, sometimes with irregular margins, and white with sulfur. On solid media (agar or agarose) with ferrous sulfate, microscopic colonies with low iron concentrations are formed, resulting in the appearance of an amber zone in the medium around them. With higher iron concentrations, round colonies (1 mm) that become red, brown, and hard with deposited ferric salts are produced. Liquid medium with ferrous sulfate at pH 1.6 changes from clear pale green to amber to red-brown with ferric sulfate. At pH 1.9 and above, considerable precipitation and encrustation with basic ferric sulfates (jarosite) take place.

Obligate chemolithotroph and autotroph. Oxidizes and grows on ferrous iron, pyrite, numerous sulfide minerals, sulfur, thiosulfate, or tetrathionate. Strictly aerobic. Ammonium salts and probably nitrate can be used as nitrogen source; reported to be able to fix dinitrogen. Optimum temperature: 30-35°C; growth range temperature: 10-37°C (no growth at 42°C). Optimum pH: about 2.5; growth range pH: 1.3-4.5. Isolated from many locations worldwide where oxidizable iron, sulfide mineral, and sulfur are exposed; particularly prevalent in acid drainage waters of mines for sulfide minerals, mineral leach dumps, and drainage waters from coal mines and coal or spoil heaps. Member of the Gammaproteobacteria.

Type strain: ATCC 23270, NCIB 8455.

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