Isolation of Gemmata-like and Isosphaera-like planctomycete bacteria from soil and freshwater

Abstract

New cultured strains of the planctomycete division (order Planctomycetales) of the domain Bacteria related to species in the genera Gemmata and Isosphaera were isolated from soil, freshwater, and a laboratory ampicillin solution. Phylogenetic analysis of the 16S rRNA gene from eight representative isolates showed that all the isolates were members of the planctomycete division. Six isolates clustered with Gemmata obscuriglobus and related strains, while two isolates clustered with Isosphaera pallida. A double-membrane-bounded nucleoid was observed in Gemmata-related isolates but not in Isosphaera-related isolates, consistent with the ultrastructures of existing species of each genus. Two isolates from this study represent the first planctomycetes successfully cultivated from soil.

FIG. 1.

Electron micrographs of cells of new Gemmata-like and Isosphaera-like isolates. (A) Negatively stained cell of the Gemmata-like strain JW11-2f5 showing crateriform structures (arrowhead) and coccoid cell morphology. Bar marker, 200 nm. (B) Negatively stained budding cell of Isosphaera-like strain CJuql1 showing uniform crateriform structures (arrowhead) on the mother cell and coccoid cell morphology. Bar marker, 200 nm. (C) Thin section of Gemmata-like cryosubstituted cell of strain JW3-8s0 showing the double-membrane-bounded nuclear body (NB) and nucleoid (N) enclosed within it. Bar marker, 200 nm. (D) Thin section of Isosphaera-like strain C2-3 possessing a fibrillar nucleoid (N) within a cytoplasmic compartment bounded by a single membrane (M) only. Bar marker, 200 nm.

FIG. 2.

Evolutionary distance tree derived from comparative analysis of 16S rDNAs from freshwater and soil isolates and reference strains of the order Planctomycetales. Database accession numbers are shown in parentheses after species, strain, or clone names. Bootstrap values of greater than 70% from 100 bootstrap resamplings from the distance analysis are presented at nodes. Thermotoga maritima was used as an outgroup. Isolates from this study and representative named species of the planctomycetes are indicated in bold. The scale bar represents 0.1 nucleotide substitution per nucleotide position.