Project description:Comparative proteomics analysis to evaluate the influence of varying culture conditions on a planktonic freshwater dwelling bacterium, Polynucleobacter asymbioticus that belongs to the class Gammaproteobacteria. In the present study, a type strain Polynucleobacter asymbioticus strain QLW-P1DMWA-1T (= DSM 18221 = CIP 10981) was cultured in triplicates in sterile UV-permeable polyethylene bags (~35% permeability; Whirl-Pak®, Nasco). Culturing was carried out at 4°C, 26°C and 26° C plus 30 minutes of ultraviolet radiation exposure two times a day using 100W ARIMED® B UV lamps (Cosmedico®, Germany). We have applied mass spectrometry based large-scale screening of proteins to investigate to better understanding of the survival nature of this microbe.
Project description:Polynucleobacter asymbioticus strain QLW-P1DMWA-1T represents a group of highly successful heterotrophic planktonic bacteria, dwelling in freshwater systems (lakes, ponds, and streams) across all climatic zones and across all continents. This includes habitats characterised by strongly fluctuating environmental conditions. So the experiments were designed to mimick winter and summer scenarios with additional impact of UV irradiation. Comparative transcriptomic studies were conducted to analyse gene-expression levels in contrasting experimental conditions. Overall, molecular candidates were revealed that may contribute in rapid acclimatisation of this strain in their immediate environment.
Project description:The subspecies Polynucleobacter necessarius asymbioticus (> 99% 16S rRNA similarity) has a cosmopolitan distribution and a ubiquitous occurrence in lentic freshwater habitats. We tested if the observed ubiquity of these free-living planktonic freshwater bacteria results from a euryoecious (generalist) adaptation of P. n. asymbioticus strains, or from ecological diversification within the subspecies. We developed a reverse line blot hybridization assay enabling the cultivation-independent detection of 13 groups within the subspecies in environmental samples. A set of 121 lentic freshwater habitats, spanning a broad variety of habitat types (e.g. pH levels ranging from 3.8 to 8.5) was investigated for the presence of these 13 P. n. asymbioticus groups. Statistical analyses of the reverse line blot hybridization detections revealed pronounced differences in habitat preferences of several of the groups. Their preferences differed regarding pH, conductivity, dissolved organic carbon and oxygen concentration of habitats. For some groups, differences in environmental preferences resulted even in complete niche separation between them. The revealed differences in habitat preferences suggest that the previously reported ubiquity of P. n. asymbioticus results from ecological diversification within the taxon and not from generalist adaptation of strains.
Project description:Genome comparisons based on average nucleotide identity (ANI) values of four strains currently classified as Polynucleobacter necessarius subsp. asymbioticus resulted in ANI values of 75.7-78.4 %, suggesting that each of those strains represents a separate species. The species P. necessarius was proposed by Heckmann and Schmidt in 1987 to accommodate obligate endosymbionts of ciliates affiliated with the genus Euplotes. The required revision of this species is, however, hampered by the fact, that this species is based only on a description and lacks a type strain available as pure culture. Furthermore, the ciliate culture Euplotes aediculatus ATCC 30859, on which the description of the species was based, is no longer available. We found another Euplotes aediculatus culture (Ammermann) sharing the same origin with ATCC 30859 and proved the identity of the endosymbionts contained in the two cultures. A multilocus sequence comparison approach was used to estimate if the four strains currently classified as Polynucleobacternecessarius subsp. asymbioticus share ANI values with the endosymbiont in the Ammermann culture above or below the threshold for species demarcation. A significant correlation (R2 0.98, P<0.0001) between multilocus sequence similarity and ANI values of genome-sequenced strains enabled the prediction that it is highly unlikely that these four strains belong to the species P. necessarius. We propose reclassification of strains QLW-P1DMWA-1T (=DSM 18221T=CIP 109841T), MWH-MoK4T (=DSM 21495T=CIP 110977T), MWH-JaK3T (=DSM 21493T=CIP 110976T) and MWH-HuW1T (=DSM 21492T=CIP 110978T) as Polynucleobacter asymbioticus comb. nov., Polynucleobacter duraquae sp. nov., Polynucleobacter yangtzensis sp. nov. and Polynucleobacter sinensis sp. nov., respectively.
Project description:Polynucleobacter necessarius subsp. asymbioticus strain QLW-P1DMWA-1(T) 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.
Project description:We present a survey on the distribution and habitat range of Polynucleobacter necessarius ssp. asymbioticus (PnecC), a numerically and functionally important taxon in the plankton of freshwater systems. We systematically sampled stagnant freshwater habitats in a heterogeneous 2000 km(2) area, together with ecologically different habitats outside this area. In total, 137 lakes, ponds and puddles were investigated, which represent an enormous diversity of habitats differing, e.g. in depth (< 10 cm-171 m) and pH (3.9-8.5). PnecC bacteria were detected by cultivation-independent methods in all investigated habitats, and their presence was confirmed by cultivation of strains from selected habitats representing the whole studied ecological range. The determined relative abundance of the subspecies ranged from values close to the detection limit of FISH (0.2%) to 67% (average 14.5%), and the highest observed absolute abundance was 5.3 x 10(6) cells ml(-1). Statistical analyses revealed that the abundance of PnecC bacteria was partially controlled by factors linked to concentrations of humic substances, which support the hypothesis that these bacteria utilize photodegradation products of humic substances. Based on the revealed statistical relationships, an average relative abundance of this subspecies of 20% in global freshwater habitats was extrapolated. Our study provides important implications for the current debate on ubiquity and biogeography in microorganisms.