Global phylogeography of pelagic Polynucleobacter bacteria: restricted geographic distribution of subgroups, isolation by distance and influence of climate.

Martin W. Hahn,Antonio Camacho,Ulrike Koll,Jitka Jezberová

doi:10.1111/1462-2920.12532

Martin W. Hahn, Antonio Camacho + Show 2 more

Open Access

https://doi.org/10.1111/1462-2920.12532

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Abstract

The free-living planktonic freshwater bacterium Polynucleobacter necessarius subspecies asymbioticus (> 99% 16S rRNA similarity) represents a taxon with a cosmopolitan distribution and apparently ubiquitous occurrence in lentic freshwater habitats. We tested for intra-taxon biogeographic patterns by combining cultivation-independent and cultivation methods. A culture collection of 204 strains isolated from globally distributed freshwater habitats (Arctic to Antarctica) was investigated for phylogeographic patterns based on sequences of two markers, the 16S–23S internal transcribed spacers and the glutamine synthetase gene (glnA). Genetic distance between isolates showed significant geographic distance-decay patterns for both markers, suggesting that an isolation-by-distance mechanism influences the global phylogeography. Furthermore, a couple of subgroups showed restricted geographic distributions. Strains of one subgroup were exclusively obtained from tropical sites on four continents (pantropical subgroup). Cultivation-independent methods were used to confirm the restricted geographic distributions of two subgroups. The pantropical taxon could be detected in 63% of investigated tropical habitats but not in any of 121 European freshwater samples. Physiological tests indicated that almost all strains of the pantropical subgroup failed to grow at temperatures of 4°C, while strains affiliated with other subgroups showed good growth at this temperature. This suggests that thermal adaptation is involved in phylogeographic structuring of the global Polynucleobacter population.

Highlights

An increasing number of studies suggests that the distribution of many microbial taxa shows biogeographic patterns (Bass and Boenigk, 2011; Fontaneto and Brodie, 2011; Hanson et al, 2012), but not much is known about the underlying mechanisms
In order to lessen this problem, we studied in a first step the distribution of taxa by a cultivation-based approach, and tested in a second step for absence of taxa in certain regions by using environmental DNA samples and polymerase chain reaction (PCR)-driven detection methods, i.e. cultivation-independent methods
Polar/alpine sites were located in the Arctic, the maritime Antarctic (6 habitats, 10 strains) and at high altitudes in the European alpine strains (Alps) (13 habitats, 20 strains)

Summary

Introduction

An increasing number of studies suggests that the distribution of many microbial taxa shows biogeographic patterns (Bass and Boenigk, 2011; Fontaneto and Brodie, 2011; Hanson et al, 2012), but not much is known about the underlying mechanisms Such biogeographic patterns can result from barriers to dispersal of organisms (i.e. limited gene flow in combination with mutation, selection and/or drift, which causes divergence of populations) (Hanson et al, 2012). A school of microbiologists argues that at least free-living (not host-associated) microorganisms differ from macroorganisms in the lack of any dispersal barriers or limitations (Baas Becking, 1934; Finlay, 2002; de Wit and Bouvier, 2006). Successful colonization of new habitats by microorganisms is a two-step procedure consisting of dispersal to and establishment of a population in the new

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