Dietzia natronolimnaios sp. nov. A New Member of the Genus Dietzia Isolated from an East African Soda Lake

　

Andrew DUCKWORTHa, Susan GRANTa, William GRANTa, Brian JONES*b, and Daan MEIJERb

　

a Department of Microbiology & Immunology, University of Leicester, University Road, Leicester LE1 9HN, UK

b Genencor International BV, PO Box 642, 2600 AP, Delft, The Netherlands

　

The East African soda lakes are found within the Kenyan-Tanzanian Rift Valley in areas of alkaline trachyte lava's, low rainfall and high rates of evaporite concentration (1, 2). The salinity's of these alkaline (pH 8 - 12) lakes vary from around 5% (w/v) total salts to almost saturation. The lakes are alkaline because of high concentrations of sodium carbonate (trona) and have very low concentrations of Ca²⁺ and Mg²⁺ which are insoluble as carbonate minerals under alkaline conditions. Lake Oloidien (also known as Little Lake Naivasha) at 0°49'S and 36°13'E is a moderately saline an alkaline example of a soda lake with a pH of 8.5 and conductivity values of around 1 - 3 mS cm^-1 (compared with more normal pH values of 10 - 11 and conductivity's of 10 to > 100 mS cm^-1 exhibited by other lakes in the Riff Valley) (1, 3), representing an interesting water chemistry intermediate between adjacent neutral pH fresh water Lake Naivasha (0°46'S and 36°20'E) (conductivity 0.4 mS cm^-1) and the soda lake L. Sonachi (0°46'S and 36°16'E) (conductivity 10 mS cm^-1).

Two novel alkaliphilic aerobic organotrophic bacteria have been isolated from Lake Oloidien. The new isolates grow at pH values between 6 and 10 with a pH optimum for growth at pH 9.0 and at a salt concentration between 0 and 10% (w/v). On the basis of 16S rRNA gene sequence analysis and DNA/DNA homology these isolates are very closely related and are members of the monospecific genus Dietzia. No significant DNA hornology is detectable with the type strain of Dietzia, Dietzia maris. We propose a second species of this genus, which we name Dietzia natronolimnaios (Type strain 15LN1 = CBS 107.95).

　

1. Jones, B.E., Grant, W.D., Collins, N.C., and Mwatha, W.E. (1994) "Bacterial Diversity and Systematics" (F.G. Priest et al., Eds), Plenum Press, New York, pp. 195-229.

2. Grant, W.D. (1992) "Encyclopedia of Microbiology" (J. Lederberg, Ed.), Academic Press, London, pp. 73-80.

3. Duckworth, A.W., Grant, W.D., Jones, B.E., and Van Steenbergen, R. (1996) FEMS Microbiol. ECOl., 19, 181-191.

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