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Abstract
Five heterotrophic, aerobic, catalase- and oxidase-positive, non-motile strains were characterized from freshwater habitats located in Austria, France, Uganda, P. R. China and New Zealand. The strains shared 16S rRNA gene similarities of ≥99.3 %. The novel strains grew on NSY medium over a temperature range of 10–35 °C (two strains also grew at 5 °C and one strain grew at 38 °C) and a NaCl tolerance range of 0.0–0.3 % (four strains grew up to 0.5 % NaCl). The predominant fatty acids were C16 : 0, C18 : 1 ω7c, C12 : 0 3-OH, and summed feature 3 (including C16 : 1 ω7c). The DNA G+C content of strain MWH-MoIso2T was 44.9 mol%. Phylogenetic analysis of 16S rRNA gene sequences demonstrated that the five new strains formed a monophyletic cluster closely related to Polynucleobacter necessarius (96–97 % sequence similarity). This cluster also harboured other isolates as well as environmental sequences which have been obtained from several habitats. Investigations with taxon-specific FISH probes demonstrated that the novel bacteria dwell as free-living, planktonic cells in freshwater systems. Based on the revealed phylogeny and pronounced chemotaxonomic differences to P. necessarius (presence of >7 % C12 : 0 3-OH and absence of C12 : 0 and C12 : 0 2-OH), the new strains are suggested to represent a novel species, for which the name Polynucleobacter cosmopolitanus sp. nov. is proposed. The type strain is MWH-MoIso2T (=DSM 21490T=CIP 109840T=LMG 25212T). The novel species belongs to the minority of described species of free-living bacteria for which both in situ data from their natural environments and culture-based knowledge are available.
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