New lineage of filamentous, spore-forming, gram-positive bacteria from soil - PubMed (original) (raw)

New lineage of filamentous, spore-forming, gram-positive bacteria from soil

Linda Cavaletti et al. Appl Environ Microbiol. 2006 Jun.

Abstract

A novel bacterial strain that was isolated from an Italian soil and was designated SOSP1-21T forms branched mycelia in solid and liquid media and has a filamentous morphology similar to that of some genera belonging to the Actinobacteria. Electron microscopy showed that this organism has a grape-like appearance, resulting from interlacing of spores originating from sporophoric hyphae. Ten strains that are morphologically related to SOSP1-21T were recovered from soil. Phylogenetic analyses of 16S rRNA gene segments confirmed the relatedness of these strains to SOSP1-21T and indicated that the newly isolated strains form separate clades in a deeply branching lineage. The closest matches for the 16S rRNA sequences of all the strains (around 79% identity) were matches with representatives of the Chloroflexi, although the affiliation with this division was not supported by high bootstrap values. The strains are mesophilic aerobic heterotrophs and are also capable of growing under microaerophilic conditions. They all stain gram positive. Strain SOSP1-21T contains ornithine, alanine, glutamic acid, serine, and glycine as the peptidoglycan amino acids. In addition, an unusual level of C16:1 2OH (30%) was found in the cellular fatty acids. The G+C content of SOSP1-21T genomic DNA is 53.9%, and MK-9(H2) was the only menaquinone detected. All these data suggest that SOSP1-21T and the related strains may constitute a new division of filamentous, spore-forming, gram-positive bacteria. We propose the name Ktedobacter racemifer gen. nov., sp. nov. for strain SOSP1-21T.

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Figures

FIG. 1.

FIG. 1.

Light micrographs of strain SOSP1-21T. (a) Aerial morphology on an HSA5 plate after incubation for 4 weeks. Magnification, ×400. (b) Magnified (ca. ×2.5) image of the area in panel a indicated by the box, showing aerial hyphae and spherical spores. (c) Mycelial growth in a submerged culture after 3 days.

FIG. 2.

FIG. 2.

Appearance of strains on acidic ISP3 agar after 3 weeks. 1-21, strain SOSP1-21T; 1-85, strain SOSP1-85; 1-52, strain SOSP1-52; 1-9, strain SOSP1-9; 1-79, strain SOSP1-79; 1-1, strain SOSP1-1.

FIG. 3.

FIG. 3.

Light micrographs (obtained with a ULWD objective) of strains SOSP1-52 (A), SOSP1-1 (B), SOSP1-85 (C), and SOSP1-9 (D) on HSA5 plates after incubation for 4 weeks. Magnification, ×400.

FIG. 4.

FIG. 4.

FESEM of strain SOSP1-21T. Bars = 2 μm. See the text for details.

FIG. 5.

FIG. 5.

Maximum likelihood tree based on 1,202 aligned positions of the 16S rRNA gene. The tree was rooted using the 16S rRNA gene sequence from Methanococcus jannaschii (accession no. M59126) as the outgroup. The numbers at nodes are bootstrap values based on 100 replicated data sets; only values greater than 65 are shown. Scale bar = 10 inferred substitutions per 100 nucleotides.

FIG. 6.

FIG. 6.

Maximum likelihood tree based on 1,168 aligned positions of the 16S rRNA gene. The tree was rooted using the Aquifex pyrophilus 16S rRNA sequence (accession no. M83548) as the outgroup. The numbers at nodes are bootstrap values based on 100 replicated data sets; only values greater than 65 are shown. Scale bar = 10 inferred substitutions per 100 nucleotides. The numbers in parentheses indicate the subphylum-level groups proposed by Hugenholtz and Stackebrandt (21), as follows: 1, “_Anaerolineae_”; 2, “_Dehalococcoidetes_”; 3, Chloroflexi; 5, Thermomicrobia. There are no cultivated representatives for lineage 4. The clades of highly related sequences are clades GER1 to GER3 for isolates and clade HAW1 for environmental clones (see the text for details).

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