Pirellula sp. strain 1 (''Rhodopirellula baltica'') is a marine representative of the globally distributed and environmentally important bacterial order Planctomycetales. Here we report the complete genome sequence of a member of this independent phylum. With 7.145 megabases, Pirellula sp. strain 1 has the largest circular bacterial genome sequenced so far. The presence of all genes required for heterolactic acid fermentation, key genes for the interconversion of C1 compounds, and 110 sulfatases were unexpected for this aerobic heterotrophic isolate. Although Pirellula sp. strain 1 has a proteinaceous cell wall, remnants of genes for peptidoglycan synthesis were found. Genes for lipid A biosynthesis and homologues to the flagellar L-and P-ring protein indicate a former Gram-negative type of cell wall. Phylogenetic analysis of all relevant markers clearly affiliates the Planctomycetales to the domain Bacteria as a distinct phylum, but a deepest branching is not supported by our analyses. P irellula sp. strain 1, which is in the process of being validly described as ''Rhodopirellula baltica,'' is a marine, aerobic, heterotrophic representative of the globally distributed and environmentally important bacterial order Planctomycetales. Molecular microbial ecology studies repeatedly provided evidence that planctomycetes are abundant in terrestrial and marine habitats (1-5). For example, they inhabit phytodetrital macroaggregates in marine environments (6) and include one of the organisms known to derive energy from the anaerobic oxidation of ammonia (7). They catalyze important transformations in global carbon and nitrogen cycles. By their mineralization of marine snow particles planctomycetes have a profound impact on global biogeochemistry and climate by affecting exchange processes between the geosphere and atmosphere (8). From a phylogenetic perspective the order Planctomycetales forms an independent, monophyletic phylum of the domain Bacteria (9). It has recently been suggested to be the deepest branching bacterial phylum (10). Planctomycetes are unique in many other respects. Their cell walls do not contain peptidoglycan, the main structural polymer of most members of the domain Bacteria. They show a unique cell compartmentalization in which a single membrane separates a peripheral ribosome-free paryphoplasm from the inner riboplasm (pirellulosome). Within the riboplasm, all planctomycetes contain a condensed fibrillar nucleoid, which in Gemmata spp. is surrounded by a additional double membrane (11). These structures, together with an unusual fatty acid composition of the phospholipids, resemble eukaryotes rather than a representative of the bacterial domain (12).Characteristic for Planctomycetales are the polar cell organization and a life cycle with a polar, yeast-like cell division. Cells attach to surfaces at their vegetative poles by means of an excreted holdfast substance or stalks (13). Further unusual features are the crateriform structures on the cell surface of all planctomycetes (14). They appear as...

The group of planctomycetes represents a separate line of descent within the domain Bacteria. Two phylum-specif ic 16s rRNA-targeted oligonucleotide probes for planctomycetes have been designed, optimized for in situ hybridization and used in different habitats to detect members of the group in situ. The probes, named PLA46 and PLA886, are targeting all or nearly all members of the planctomycete line of descent. Planctomycetes could be detected in almost all samples examined, e.g. a brackish water lagoon, activated sludge, and other wastewater habitats. In situ probing revealed quite uniform morphology and spatial arrangement of the detected cells but profound differences in abundance ranging from less than 01 YO to several percentage of the total cells. Single coccoid cells with diameters between I and 2.5 pm were dominating in most samples with the exception of the lagoon, in which rosettes of pear-shaped cells were abundant. The planctomycetes showed generally no hybridization signals with the bacterial probe EUB338, which is in accordance with base changes in their 165 rRNA sequences. A discrete ultrastructure of planctomycete cells was suggested by double staining with rRNA-targeted probes and the DNA-binding dye 4',6-diamidino-2-phenylindole (DAPI). The probe-conferred fluorescence was distributed in a ring-shaped manner around a central DAPI spot. The two probes developed extend the existing set of group-specif ic rRNA-targeted probes and help to elucidate the basic composition of bacterial communities in a first step of differential analysis. In situ hybridization of environmental samples indicated widespread presence of planctomycetes in different ecosystems.

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Ninety-seven strains of budding bacteria originating from various aquatic habitats and morphologically resembling planctomycetes were investigated taxonomically. Taxonomic differentiation was based on DNA–DNA hybridization, physiological properties and chemotaxonomic tests. Nineteen hybridization groups, containing 79 of the tested strains, were established. Eighteen strains, however, did not fit into any of these groups. Rhodopirellula baltica gen. nov., sp. nov. is described, with strain SH 1T (=IFAM 1310T=DSM 10527T=NCIMB 13988T) as the type strain. Pirellula marina is transferred to the genus Blastopirellula gen. nov. as Blastopirellula marina comb. nov., with strain SH 106T (=IFAM 1313T=DSM 3645T=ATCC 49069T) as the type strain. An emended description of the genus Pirellula is also provided. Differentiation between R. baltica, B. marina and Pirellula staleyi was achieved by the integration of morphological, physiological, chemotaxonomic and genetic characteristics.