An extremely halophilic red micro-organism designated strain TM(T) was isolated from a solar saltern in Alexandria, Egypt. The micro-organism stains gram-negative, is very pleomorphic, non-motile and strictly aerobic and requires at least 10 g NaCl l(-1) for growth. The growth optimum is 250 g NaCl l(-1). Growth is also observed over a wide range of MgSO4 concentrations (10-40 g l(-1)). Aerobic reduction of nitrate without gas production was detected. Cells grew aerobically in a minimal salts medium containing ammonium chloride and glucose. Strain TM(T) produced acid from fructose, glucose, rhamnose, maltose and glycerol. The G+C content of the DNA was 59.5+/-0.3 mol %. On the basis of polar lipid analysis, the isolate belonged to the genus Haloferax. Analysis of the 16S rDNA sequence showed the highest similarity (>99%) to be to the type strain Haloferax volcanii. Although the spectrum of antibiotic susceptibility was similar to that of validly described species of the genus Haloferax, the strain could be distinguished from them by its different response to josamycin and rifampicin. Strain TM(T) is unique within the genus Haloferax in producing canthaxanthin. Comparative analysis of phenotypic properties and DNA-DNA hybridization between strain TM(T) and Haloferax species supported the conclusion that TM(T) is a novel species within this genus, for which the name Haloferax alexandrinus sp. nov. is proposed. The type strain is TM(T) (= JCM 10717T = IFO 16590T).


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