Planctomicrobium piriforme gen. nov., sp nov., a stalked planctomycete from a littoral wetland of a boreal lake

An aerobic, budding, non-pigmented and rosette-forming bacterium was isolated from a littoral wetland of a boreal lake located in Valaam Island, northern Russia,, and designated strain P3(T). Ellipsoidal to pear-shaped cells of this bacterium were covered with crateriform pits and possessed stalks suggesting a planctomycete morphotype. 16S rRNA gene sequence analysis confirmed that strain P3T was a member of the order Planctomycetales and belonged to a phylogenetic lineage defined by the genus Planctomyces, with 89 and 86% sequence similarity to Planctomyces brasiliensis and Planctomyces mans, respectively. Strain P3T was a mildly acidophilic, mesophilic organism capable of growth at pH values between pH 4.2 and 7.1 (with an optimum at pH 6.0-6.5) and at temperatures between 10 and 30 degrees C (optimum at 20-28 degrees C). Most sugars, a number of polysaccharides and several organic acids were the preferred growth substrates. Compared with Planctomyces brasiliensis and Planctomyces maris, which require NaCl for growth, strain P3T was salt-sensitive and did not develop at NaCl concentrations above 0.5% (w/v). The major fatty acids were C-16:0 and C-16:1 omega 7c; the cells also contained significant amounts of C-18:1 omega 7c and C-18:0. The major intact polar lipids were diacylglycerol-O-(N,N,N-trimethyl)homoserine (DGTS) lipids; the major neutral lipids were long-chain 1,(omega-1)-diols and C-31:9 hydrocarbon. The quinone was MK-6, and the G+C content of the DNA was 59.0 mol%. Strain P3T differed from Planctomyces brasiliensis and Planctomyces mans by cell morphology, substrate utilization pattern and a number of physiological characteristics. Based on these data, the novel isolate should be considered as representing a novel genus and species of planctomycetes, for which the name Planctomicrobium piriforme gen. nov., sp. nov., is proposed. The type strain is P3(T) (=DSM 26348(T)=VKM B-2887(T)).