Polynucleobacter asymbioticus

Polynucleobacter asymbioticus is an aerobic, catalase- and oxidase-positive, chemo-organotrophic, nonmotile, free-living bacterium of the genus Polynucleobacter. The type strain was isolated from a small pond located in the Austrian Alps in the area of Salzburg[2] and described as a new subspecies of Polynucleobacter necessarius in 2009.[3] The classification of the type strain was hampered by the fact that its closest described relative represented obligate endosymbionts, i.e. P. necessarius, not available as a pure culture suitable for standard tests (DNA-DNA hybridization experiments) for delineation of prokaryotic species. Therefore, the strain was preliminarily placed in the subspecies P. necessarius subsp. asymbioticus. Later sequencing of the genome of the type strain[4] revealed that the strain represented a novel species within the genus Polynucleobacter. Therefore, its taxonomic rank was lifted from the subspecies to the species level.[5] Strains of P. asymbioticus dwell as planktonic organisms in acidic, humic-rich freshwater systems.[6] Comparative genome analyses revealed that P. asymbioticus represents an atypical member of the family Burkholderiaceae regarding its small genome size and its passive lifestyle.[7] A recent study used a collection of 37 P. asymbioticus strains isolated from various ponds located in a larger region of the Austrian Alps to gain insights in the evolution of Polynucleobacter bacteria.[8]