Differentiation of the genus Arhodomonas from

other genera

The 16S rDNA sequence similarity shows that A. aquaeolei is related to Ectothiorhodospiraceae and is most similar to Halorhodospira (Fig. BXII.y.19 of the chapter describing the family Ectothiorhodospiraceae; Imhoff and Suling, 1996). It is clearly distinguished from these phototrophic bacteria by its strictly chemotrophic metabolism, its inability to grow phototrophically, and its lack of photosynthetic pigments. It shares the requirement for high salt concentrations with Halorhodospira species and in addition has a restricted spectrum of carbon sources, similar to those of its pho-totrophic relatives (Imhoff, 1989, 1992). Some properties of A. aquaeolei that differentiate it from other genera of the Ectothio-rhodospiraceae are shown in Table BXII.y.7 of the chapter describing the family Ectothiorhodospiraceae.

Further Reading

Adkins, J.P., M.T. Madigan, L. Mandelco, C.R. Woese and R.S. Tanner. 1993. Arhodomonas aquaeolei gen. nov., sp. nov., an aerobic, halophilic bacterium isolated from a subterranean brine. Int. J. Syst. Bacteriol. 43: 514-520.

Imhoff, J.F. and J. Suling. 1996. The phylogenetic relationship among Ectothiorhodospiraceae: a reevaluation of their taxonomy on the basis of 16S rDNA analyses. Arch. Microbiol. 165: 106-113.

List of species of the genus Arhodomonas

1. Arhodomonas aquaeolei Adkins, Madigan, Mandelco, Woese and Tanner 1993, 518VP

a.quae.o' le.i. L. gen. n. aquae of the water; L. gen. n. olei of the oil; M.L. gen. n. aquaeolei from water of oil.

Cells are straight, short rods, 0.8-1.0 X 2.0-2.5 |im and motile by means of a single polar flagellum. Metabolism is strictly chemotrophic. Simple organic compounds such as acetate, propionate, lactate, butyrate, valerate, isovalerate, ethanol, glycerol, glutamic acid, glutamine, and xylose are used as substrates for aerobic chemotrophic growth. Glucose, fructose, sucrose, mannose, maltose, lactose, citrate, alanine, aspartic acid, asparagine, histidine, arginine, ser-

ine, and tryptophan are not used. Nitrate, but not nitrite, is reduced. Oxidase, catalase, and urease are present, but arginine, lysine, and ornithine decarboxylases are absent. Hydrolysis of Tween 80 is positive, while casein, DNA, es-culin, gelatin, and starch are not hydrolysed. Cells are sensitive to chloramphenicol, penicillin, and tetracycline.

Mesophilic and extremely halophilic bacterium with optimum growth at 15% NaCl (range: 6-20%).

Habitat: oil field brine.

Type strain: HA-1, ATCC 49307.

GenBank accession number (16S rRNA): M26631.

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