- Volume 42, Issue 1, 1992

The 16S rRNA primary structures of Eubacterium suis DSM 20639T (T = type strain) and Bifidobacterium bifidum DSM 20456T were determined by sequencing in vitro amplified rDNA. Sequence comparisons indicated that B. bifidum is moderately related to representatives of the genera Actinomyces and Mobiluncus. The closest relative of E. suis is Actinomyces pyogenes. E. suis and A. pyogenes are more closely related phylogenetically to one another than to the other Actinomyces species that have been investigated by using comparative 16S rRNA analysis. Therefore, we propose that E. suis should be transferred to the genus Actinomyces as Actinomyces suis comb. nov.

16S rRNA (genes coding for rRNA) sequence comparisons were conducted with the following three psychrophilic strains: Bacillus globisporus W25T (T = type strain) and Bacillus psychrophilus W16AT, and W5. These strains exhibited more than 99.5% sequence identity and within experimental uncertainty could be regarded as identical. Their close taxonomic relationship was further documented by phenotypic similarities. In contrast, previously published DNA-DNA hybridization results have convincingly established that these strains do not belong to the same species if current standards are used. These results emphasize the important point that effective identity of 16S rRNA sequences is not necessarily a sufficient criterion to guarantee species identity. Thus, although 16S rRNA sequences can be used routinely to distinguish and establish relationships between genera and well-resolved species, very recently diverged species may not be recognizable.

The genomic relatedness between Listeria grayi and Listeria murrayi was reevaluated by using DNA-DNA hybridization, multilocus enzyme electrophoresis, and rRNA restriction fragment length polymorphism techniques. The high levels of similarity observed between the strains of these two species confirmed the data published since 1973 and indicated that they should be considered members of a single species. On grounds of priority, the species should be named L. grayi.

Growth at temperatures of >60°C and utilization of polysaccharides have not been reported previously in members of the genus Spirochaeta. Two obligately anaerobic, extremely thermophilic (optimum temperature, 65°C) spirochetes were isolated from geographically distant thermal sites. These two isolates have chemoorganotrophic fermentative metabolism and grow on a variety of mono-, di-, and polysaccharides, including cellulose. The differences in pH and NaCl concentration optima between these organisms reflect the prevailing conditions at the sites from which they were isolated. DNA-DNA hybridization showed that the two strains exhibit a level of homology of 87%. On the basis of their morphological characteristics, their high level of homology with each other, and their extremely thermophilic and polysaccharolytic nature, we propose that these organisms should be included in the genus Spirochaeta as a new species, Spirochaeta thermophila; the type strain of this species is strain Z-1203 (= DSM 6578).

Urealytic strains of coryneform bacteria that are designated Corynebacterium group D2 and are isolated from human urine are a cause of urinary tract infections. Cell wall and lipid analyses confirmed that these organisms are members of the genus Corynebacterium but can be separated from other species in the genus on the basis of DNA base composition and DNA-DNA hybridization values. Biochemically, strains in this taxon can be distinguished from other Corynebacterium spp. by their failure to produce acid from carbohydrates, by their failure to reduce nitrates, and by their ability to hydrolyze urea. We regard these bacteria as a new species of the genus Corynebacterium and propose the name Corynebacterium urealyticum. The type strain is strain NCTC 12011 (= ATCC 43042).

Average DNA base compositions, as determined from 50% thermal denaturation temperatures and from buoyant densities, were 38, 41, 43, and 40 to 41 mol% G+C for Microcystis sp. strains P1-15, C5-34, AK1-6, and C3-40, respectively. These phenotypically similar organisms, which are representatives of the Microcystis cluster within the Synechocystis group of chroococcacean cyanobacteria, have a smaller range of DNA base compositions (38 to 43 mol% G+C) than the Synechocystis group as a whole does (30 to 48 mol% G+C). Because the DNA base ratios of the Microcystis cultures adjoin or overlap those of the low- and high-G+C-content clusters of the Synechocystis group, DNA base composition data do not differentiate the Microcystis cluster from these two Synechocystis clusters. By bridging the gap between the low- and high-G+C-content clusters of the Synechocystis group, the data for Microcystis create a continuum of DNA base ratios within the Synechocystis group and diminish the usefulness of G+C values for discerning clusters within the phenotypically heterogeneous Synechocystis group.

There are two validly published species names, Flexibacter maritimus Wakabayashi, Hikida, and Masumura 1986 (with strain NCMB 2154 as the type strain) and Cytophaga marina Reichenbach 1989 (with strain NCMB 2153 as type strain), for what is clearly the same organism. Both type strains were included in the original description of F. maritimus. The proposal of C. marina was intended as a new combination for “Flexibacter marinus,” a name that was never validly published but was used for the same organism for which F. maritimus was eventually proposed. F. maritimus clearly has priority.

Phenotypic, chemotaxonomic, and DNA-DNA hybridization studies of strains of Rhodopseudomonas rutila Akiba et al. 1983 and Rhodopseudomonas palustris (Molisch 1907) van Niel 1944 demonstrated synonymy between the two species. We propose that they be classified into a single species, retaining the name R. palustris.

The bacterial genus Serpula Stanton et al. 1991 is illegitimate due to the existence of a fungal genus Serpula Pers. ex S. F. Gray. Consequently, a new genus designation, Serpulina, is proposed for this spirochete genus. Serpula hyodysenteriae, the type species, and Serpula innocens Stanton et al. 1991, therefore, become Serpulina hyodysenteriae comb. nov. and Serpulina innocens comb. nov.

The inclusion of “Pseudomonas maltophilia” Hugh 1981 in the genus Xanthomonas as Xanthomonas maltophilia (Hugh 1981) Swings et al. 1983 is questioned in view of the significant differences between these two taxa. This reclassification is not acceptable if practical means of differentiation in this genus are considered. The proposed alteration of the description of the genus Xanthomonas is also questionable because of the implications for everyday phytobacteriology. In view of the natural similarities, as well as the profound differences, between X. maltophilia and the genus Xanthomonas, we propose that a new genus should be created for X. maltophilia, which could be placed together with the genus Xanthomonas in a separate natural group.