Tundrisphaera lichenicola gen. nov., sp nov., a psychrotolerant representative of the family Isosphaeraceae from lichen-dominated tundra soils

Two strains of aerobic, budding, pink-pigmented bacteria, P12(T) and P515, were isolated from a lichen-dominated peatland and a forested tundra soil of north-western Siberia, respectively. Cells of these isolates were represented by non-motile spheres that occurred singly or were arranged in short chains and aggregates. While growing on solid media, cells of strains P12(T) and P515 attached to the surface by means of holdfast-like appendages. These isolates were mildly acidophilic (optimum growth at pH 5.5-6.0), psychrotolerant bacteria, which displayed tolerance of low temperatures (4-15 degrees C), grew optimally at 15-22 degrees C and did not grow at temperatures above 28 degrees C. The preferred growth substrates were sugars and some heteropolysaccharides. The major fatty acids were C-18:1 omega 9c, C-16:0 and C-14:0. Trimethylornithine lipid was the major polar lipid. The only quinone was MK-6, and the G+C content of the DNA was 61.2-62.2 mol%. Strains P12(T) and P515 possessed identical 16S rRNA gene sequences, which affiliated them with the family Isosphaeraceae, order Planctomycetales, and these displayed the highest similarity (93-94 %) to 16S rRNA gene sequences from members of the genus Singulisphaera. However, the signature fatty acid of species of the genus Singulisphaera, i. e. C-18:2 omega 6c, 12c, was absent in cells of strains P12(T) and P515. They also differed from members of the genus Singulisphaera by 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 Tundrisphaera lichenicola gen. nov., sp. nov, is proposed. The type strain is P12(T) (= LMG 29571(T) = VKM B-3044(T)).