Paludisphaera borealis gen. nov., sp. nov., a hydrolytic planctomycete from northern wetlands, and proposal of Isosphaeraceae fam. nov.

Abstract

Two isolates of aerobic, budding, pink-pigmented bacteria, designated strains PX4^T and PT1, were isolated from a boreal <i>Sphagnum</i> peat bog and a forested tundra wetland. Cells of these strains were non-motile spheres that occurred singly or in short chains. Novel isolates were capable of growth at pH values between 3.5 and 6.5 (optimum at pH 5.0-5.5) and at temperatures between 6 and 30 °C (optimum at 15-25 °C). Most sugars and a number of polysaccharides including pectin, xylan, lichenin and Phytagel were used as growth substrates. The major fatty acids were C_{16 : 0}, C_{18 : 1}ω9 and C_{18 : 0}; the major polar lipids were phosphocholine and trimethylornithine. The quinone was menaquinone-6, and the G+C content of the DNA was 66 mol%. Strains PX4^T and PT1 were members of the order <i>Planctomycetales</i> and displayed 93-94 % 16S rRNA gene sequence similarity to <i>Aquisphaera giovannonii</i>, 91-92 % to species of the genus <i>Singulisphaera</i> and 90-91 % to <i>Isosphaera pallida</i>. The two novel strains, however, differed from members of these genera by cell morphology, substrate utilization pattern and a number of physiological characteristics. Based on these data, the novel isolates should be considered as representing a novel genus and species of planctomycetes, for which the name <i>Paludisphaera borealis</i> gen. nov., sp. nov., is proposed. The type strain is PX4^T ( = DSM 28747^T = VKM B-2904^T). We also suggest the establishment of a novel family, <i>Isosphaeraceae</i> fam. nov., to accommodate stalk-free planctomycetes with spherical cells, which can be assembled in short chains, long filaments or shapeless aggregates. This family includes the genera <i>Isosphaera, Aquisphaera, Singulisphaera</i> and <i>Paludisphaera</i>.