Abstract
Polynucleobacter necessarius subsp. asymbioticus strain QLW-P1DMWA-1T is a planktonic freshwater bacterium affiliated with the family Burkholderiaceae (class Betaproteobacteria). This strain is of interest because it represents a subspecies with cosmopolitan and ubiquitous distribution in standing freshwater systems. The 16S-23S ITS genotype represented by the sequenced strain comprised on average more than 10% of bacterioplankton in its home habitat. While all strains of the subspecies P. necessarius asymbioticus are free-living freshwater bacteria, strains belonging to the only other subspecies, P. necessarius subsp. necessarius are obligate endosymbionts of the ciliate Euplotes aediculatus. The two subspecies of P. necessarius are the instances of two closely related subspecies that differ in their lifestyle (free-living vs. obligate endosymbiont), and they are the only members of the genus Polynucleobacter with completely sequenced genomes. Here we describe the features of P. necessarius subsp. asymbioticus, together with the complete genome sequence and annotation. The 2,159,490 bp long chromosome with a total of 2,088 protein-coding and 48 RNA genes is the first completed genome sequence of the genus Polynucleobacter to be published and was sequenced as part of the DOE Joint Genome Institute Community Sequencing Program 2006.
Highlights
Strain QLW-P1DMWA-1T (= DSM 18221 = CIP 10981) is the type strain of Polynucleobacter necessarius subsp. asymbioticus [1], which is one of two subspecies in the species P. necessarius [1]
The description of P. necessarius subsp. asymbioticus followed several years after the observation that these free-living planktonic bacteria are closely related to P. necessarius and are cosmopolitan in freshwater habitats, occurring in different climatic zones in Europe, Asia and Africa [4]
P. necessarius, initially described as a taxon exclusively harboring obligate endosymbionts of E. aediculatus [2], is one of a small number of bacterial species with a validly published name for which an axenic culture of a type strain does not exist in a public strain collections [1], all of which predate the introduction of the Candidatus concept [41]
Summary
Strain QLW-P1DMWA-1T (= DSM 18221 = CIP 10981) is the type strain of Polynucleobacter necessarius subsp. 22 years later, Hahn et al described a closely related free-living strain, QLWP1DMWA-1T, which they considered to be another. Asymbioticus followed several years after the observation that these free-living planktonic bacteria are closely related to P. necessarius and are cosmopolitan in freshwater habitats, occurring in different climatic zones in Europe, Asia and Africa [4]. This observation was confirmed by several cultivationindependent investigations of freshwater bacterioplankton diversity (for review see Newton et al, 2011 [5]). We present a summary classification and a set of features for P. necessarius subsp. asymbioticus QLW-P1DMWA1T, together with the description of the complete genomic sequencing and annotation
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