Vol. 26, No. 2 Printed in U . S A .
Phenotypic Description, Numerical Analysis, and Proposal for an Improved Taxonomy and Nomenclature of the Genus Zymomonas Kluyver and van Niel 1936 J. DE LEY
Microbiology and Microbial Genetics, Faculty of Sciences, State University, K . L . Ledeganckstraat 35, B-9000 Gent, Belgium
One hundred thirty-eight phenotypic features were determined in 38 Zymomonas strains from diverse origin (Zairese fermenting palm saps, Mexican pulque, British spoiled beer, and sick cider). The similarity between all the strains was very high: 27 features were present, and 74 features were absent in all of them; 37 features were variable. By numerical analysis all strains formed one cluster above the simple matching coefficient of 0.88. There were no significant differences between motile and nonmotile strains or between sucrosefermenting and non-sucrose-fermenting strains. A strain from sick cider in Bristol, United Kingdom, was a border case in its phenotypic features, deoxyribonucleic acid relatedness, and protein electropherograms. We propose: (i) to discontinue the use of the species name of Zymomonas anaerobia and its subspecies Z. anaerobia subsp. anaerobia and 2. anaerobia subsp. irnmobilis, and to include all of the strains in this species in Zymomonas mobilis; (ii) to consider Zymomonas congolensis as a nomen nudum and as a synonym of 2. mobilis. We concluded the following from our data: that 2. mobilis is the only species in the genus Zymomonas so far; that all the strains of our Zymomonas collection except one belong in 2. mobilis subsp. mobilis, the type strain of which is ATCC 10988; and that the cider sickness organisms belong in 2. mobilis subsp. pomaceae (Millis) comb. nov., with type strain T. H. Delft ( = strain I [Barker] = ATCC 29192). The taxonomy of the genus Zyrnomonas Kluyver and van Niell936 has not been studied extensively, the main reason being that only a few strains belonging to this genus have been known. We collected some 40 strains, mainly from fermenting palm saps, fermenting Agave sap, deteriorated British beers, and sick cider. All of our strains, except one, had very similar deoxyribonucleic acid (DNA) base composition, genome size, and DNA relatedness (homology) (27). Close genetic relatedness suggests considerable phenotypic similarity. Indeed, the protein electropherograms of all strains, except one, were almost indistinguishably the same. The exception was the cider sickness organism, received as Zymomonas anaerobia var. pomaceae (J. Swings, K. Kersters, and J. De Ley, J. Gen. Microbiol., in press). In the present work we present the phenotypic description of 38 Zymomonas strains and the numerical analysis of 136 features. biol., in press). They were maintained and grown on a standard medium containing (wthol) 2% glucose and 0.5% yeast extract (Difco) in distilled water. Methods of testing, All tests were performed under the following conditions, except when otherwise stated. Inoculations of all liquid test media were made with one drop of a starter culture, 24 h old. The incubation temperature was 30 C. Most tests were followed for up t o 3 weeks. Morphological features. The size of 24-h-old cells was measured on microphotographs from at least three areas in a fixed preparation, stained with 3% basic fuchsin for 1min. Hucker Gram stain, Burdon lipid stain, Bartholomew and Mittwer stain for spores, and Anthony stain for capsules (25) were performed on cultures grown for 24 h in a standard medium. Intracellular glycogen was detected with Eugol I2 solution. Rosette formation and motility were determined by direct microscope observation of 12- to 24-h-old liquid cultures. Rhodes’ method (10) was used for the detection of flagella. Carbohydrates and derivatives as carbon source for...