Evidence of adaptation, niche separation and microevolution within the genus Polaromonas on Arctic and Antarctic glacial surfaces

Abstract

Polaromonas is one of the most abundant genera found on glacier surfaces, yet its ecology remains poorly described. Investigations made to date point towards a uniform distribution of Polaromonas phylotypes across the globe. We compared 43 Polaromonas isolates obtained from surfaces of Arctic and Antarctic glaciers to address this issue. 16S rRNA gene sequences, intergenic transcribed spacers (ITS) and metabolic fingerprinting showed great differences between hemispheres but also between neighboring glaciers. Phylogenetic distance between Arctic and Antarctic isolates indicated separate species. The Arctic group clustered similarly, when constructing dendrograms based on 16S rRNA gene and ITS sequences, as well as metabolic traits. The Antarctic strains, although almost identical considering 16S rRNA genes, diverged into 2 groups based on the ITS sequences and metabolic traits, suggesting recent niche separation. Certain phenotypic traits pointed towards cell adaptation to specific conditions on a particular glacier, like varying pH levels. Collected data suggest, that seeding of glacial surfaces with Polaromonas cells transported by various means, is of greater efficiency on local than global scales. Selection mechanisms present of glacial surfaces reduce the deposited Polaromonas diversity, causing subsequent adaptation to prevailing environmental conditions. Furthermore, interactions with other supraglacial microbiota, like algae cells may drive postselectional niche separation and microevolution within the Polaromonas genus.

Keywords: 16S rRNA gene; Bacteria; Biogeography; Glacier; ITS; Polaromonas.

Fig. 1

Phylogenetic tree constructed using complete 16S rRNA gene sequences of Polaromonas isolates. Isolate designations indicate the hemisphere and glacier of origin (N Arctic, S Antarctica, H Hans Glacier, W Werenskiold Glacier, E Ecology Glacier). The tree was built with the neighbor-joining method. Bootstrap values are indicated at the nodes. R. ferrireducens strain T118 sequence has been used as an outgroup

Fig. 2

Phylogenetic tree constructed using complete ITS sequences of Polaromonas isolates. Isolate designations indicate the hemisphere and glacier of origin (N Arctic, S Antarctica, H Hans Glacier, W Werenskiold Glacier, E Ecology Glacier). The tree was built with the neighbour-joining method. Bootstrap values are indicated at the nodes. R. ferrireducens strain T118 sequence has been used as outgroups. ➀ ITS Ecology Glacier group 1; ➁ ITS Ecology Glacier group 2

Fig. 3

Dendrogram constructed using data obtained from GENIII microplate metabolic features of Polaromonas isolates. Isolate designations indicate the hemisphere and glacier of origin (N Arctic, S Antarctica, H Hans Glacier, W Werenskiold Glacier, E Ecology Glacier). ➀ ITS Ecology Glacier group 1; ➁ ITS Ecology Glacier group 2

Fig. 4

Number of positive reactions in GENIII microplates of Polaromonas isolates from a particular glacier. Asterisk indicates a statistical significance of p < 0.05

Fig. 5

Principal component analysis clustering of isolates based on 16S rRNA gene, ITS sequences and metabolic fingerprinting. Square Ecology Glacier isolates, Triangle Hans Glacier isolates, Circle Werenskiold Glacier isolates

Fig. 6

Microphotograph of algae and bacteria agglomerate from Ecology Glacier surface: a DAPI stained bacterial cells (black arrow) imbedded in extracellular matrix of a round algae cell (under UV light). b Autofluorescence of the same algae cell under green-light excitation