Stieleria varia sp. nov., isolated from wood particles in the Baltic Sea, constitutes a novel species in the family Pirellulaceae within the phylum Planctomycetes

Abstract

Species belonging to the bacterial phylum Planctomycetes are ubiquitous members of the microbial communities in aquatic environments and are frequently isolated from various biotic and abiotic surfaces in marine and limnic water bodies. Planctomycetes have large genomes of up to 12.4 Mb, follow complex lifestyles and display an uncommon cell biology; features which motivate the investigation of members of this phylum in greater detail. As a contribution to the current collection of axenic cultures of Planctomycetes, we here describe strain Pla52^T isolated from wood particles in the Baltic Sea. Phylogenetic analysis places the strain in the family Pirellulaceae and suggests two species of the recently described genus Stieleria as current closest neighbours. Strain Pla52n^T shows typical features of members of the class Planctomycetia, including division by polar budding and the presence of crateriform structures. Colonies of strain Pla52n^T have a light orange colour, which is an unusual pigmentation compared to the majority of members in the phylum, which show either a pink to red pigmentation or entirely lack pigmentation. Optimal growth of strain Pla52n^T at 33 °C and pH 7.5 indicates a mesophilic (i.e. with optimal growth between 20 and 45 °C) and neutrophilic growth profile. The strain is an aerobic heterotroph with motile daughter cells. Its genome has a size of 9.6 Mb and a G + C content of 56.0%. Polyphasic analyses justify delineation of the strain from described species within the genus Stieleria. Therefore, we conclude that strain Pla52n^T = LMG 29463^T = VKM B-3447^T should be classified as the type strain of a novel species, for which we propose the name Stieleria varia sp. nov.

Keywords: Biotic surfaces; Budding bacteria; Marine bacteria; Secondary metabolites; Stieleriacines.

Fig. 1

Maximum likelihood phylogenetic analysis of strain Pla52n^T. Phylogenetic trees based on 16S rRNA gene sequences and MLSA were computed as described in the Materials and methods section. Bootstrap values after 1000 re-samplings (16S rRNA gene)/500 re-samplings (MLSA) are given at the nodes (in %). The outgroup in the 16S rRNA gene-based tree consists of 16S rRNA genes from three strains outside of the phylum Planctomycetes but part of the PVC superphylum. In the MLSA tree the genomes of Planctopirus limnophila and Gimesia maris (both family Planctomycetaceae) served as outgroup

Fig. 2

Analysis of phylogenetic markers used for the delineation of strain Pla52n^T from characterised species of the genus Stieleria. Analysed markers included 16S rRNA gene sequence similarity (16S), average amino acid identity (AAI), average nucleotide identity (ANI), identity of a 1200 bp fragment of the gene rpoB and percentage of conserved proteins (POCP)

Fig. 3

Microscopy images and cell size plot of strain Pla52n^T. The mode of cell division (a) and a general overview of cell morphology (b, d, e) is shown in the micrographs, respectively. For determination of the cell size (c) at least 100 representative cells were counted manually or by using a semi-automated object count tool

Fig. 4

Temperature and pH optimum of strain Pla52n^T. The graphs show the average growth rates obtained from cultivation in M1H NAG ASW medium in biological triplicates. Cultivations at different pH values were conducted at 28 °C and cultivations at different temperatures were performed at pH 7.5