Reclassification of Gluconacetobacter hansenii strains and proposals of Gluconacetobacter saccharivorans sp. nov. and Gluconacetobacter nataicola sp. nov.

Ten strains previously assigned to Acetobacter hansenii (=Gluconacetobacter hansenii), Acetobacter pasteurianus LMG 1584 and eight reference strains of the genus Gluconacetobacter were reclassified by 16S rRNA gene sequencing, DNA-DNA similarity, DNA base composition and phenotypic characteristics. The A. hansenii strains and A. pasteurianus LMG 1584 were included in the cluster of acetic acid bacteria (family Acetobacteraceae) by 16S rRNA gene sequences. Further, they were separated into seven distinct groups by DNA-DNA similarity. DNA-DNA similarity group I was identified as G. hansenii. DNA-DNA similarity group II was retained as Gluconacetobacter sp., because DNA-DNA similarity between the strain and Gluconacetobacter entanii LTH 4560(T) could not be determined. This was due to a lack of availability of the type strain from any source. DNA-DNA similarity group III was regarded as a novel species, for which the name Gluconacetobacter saccharivorans sp. nov. (type strain, LMG 1582(T)=NRIC 0614(T)) is proposed. DNA-DNA similarity group IV included the type strains of Gluconacetobacter oboediens and Gluconacetobacter intermedius, and three A. hansenii strains. This group was identified as G. oboediens because high values of DNA-DNA similarity were obtained between the type strains and G. oboediens has priority over G. intermedius. DNA-DNA similarity group V was identified as Gluconacetobacter europaeus. DNA-DNA similarity group VI was regarded as a novel species, for which the name Gluconacetobacter nataicola sp. nov. (type strain, LMG 1536(T)=NRIC 0616(T)) is proposed. DNA-DNA similarity group VII was reclassified as Gluconacetobacter xylinus. The description of G. hansenii is emended.

Differentiation of Gluconacetobacter liquefaciens and Gluconacetobacter xylinus on the basis of DNA base composition, DNA relatedness, and oxidation products from glucose.

Gluconacetobacter liquefaciens and Gluconacetobacter xylinus share very similar phenotypic characteristics. They are differentiated by the production of a reddish-brown water-soluble pigment of the former and cellulose production of the latter. However, the loss of the two distinguishing features questions the separate standings of the two species. The DNA base composition and the DNA relatedness of strains of the two species, including other established species of acetic acid bacteria, were determined. G. liquefaciens strains had the higher guanine-plus-cytosine content (G+C content) in DNA, ranging from 63.5 to 66.9 mol%, and G. xylinus had the lower range, from 59.4 to 63.2 mol%. DNA hybridization revealed a low level of DNA similarity between the two species. G. liquefaciens strains produced 2,5-diketogluconic acid and pyrones from glucose, and G. xylinus strains produced 5-ketogluconic acid. From these results, it is unequivocal that G. liquefaciens is a distinct species from G. xylinus.

Taxonomic heterogeneity of strains comprising Gluconacetobacter hansenii.

The taxonomic standing of Gluconacetobacter hansenii was clarified through phenotypic characteristics, quinones, DNA base composition, DNA relatedness, and the production of gluconic and ketogluconic acids from glucose. All strains that Gosselé et al. (Syst. Appl. Microbiol., 4, 338-368, 1983) employed in the establishment of Acetobacter hansenii (=G. hansenii) were used in this study. Phenotypic differences were shown among the strains of G. hansenii, suggesting heterogeneity within the species. The major ubiquinone was Q-10 for all strains of G. hansenii, except for strain IFO 3296, which was characterized by Q-9. This excluded IFO 3296 from the species G. hansenii and placed it in the genus Acetobacter. DNA relatedness revealed four distinct homology groups (I, II, III, and IV) among strains of the species. Group I was distinguished from the other genomic groups by a lower G1C range from 58.9 to 59.2 mol%. Groups II, III, and IV showed higher G+C contents of 60.4 to 62.2, 60.8, and 61.7 mol%, respectively. Groups I and IV produced both 2- and 5-ketogluconic acids from glucose, and Group III produced only 2-ketogluconic acid. Group II included strains that produced both 2- and 5-ketogluconic acids and strains that produced only 2-ketogluconic acid. It is clear that G. hansenii consists of genotypically heterogeneous strains comprising four homology groups (I, II, III, and IV). Since group I contains the type strain (IFO 14820(T)=LMG 1527(T)) of the species, this group is designated as the species G. hansenii.