Microbial Consortium Associated with the Antarctic Marine Ciliate Euplotes focardii: An Investigation from Genomic Sequences.

Sandra Pucciarelli,Patrizia Ballarini,Martina Schrallhammer,Michele Castelli,Giulio Petroni,Alessio Mancini,Cristina Miceli,Raghul Rajan Devaraj

doi:10.1007/s00248-015-0568-9

Sandra Pucciarelli, Patrizia Ballarini + Show 6 more

Open Access

https://doi.org/10.1007/s00248-015-0568-9

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Abstract

We report the characterization of the bacterial consortium associated to Euplotes focardii, a strictly psychrophilic marine ciliate that was maintained in laboratory cultures at 4 °C after its first isolation from Terra Nova Bay, in Antarctica. By Illumina genome analyser, we obtained 11,179 contigs of potential prokaryotic origin and classified them according to the NCBI’s prokaryotic attributes table. The majority of these sequences correspond to either Bacteroidetes (16 %) or Proteobacteria (78 %). The latter were dominated by gamma- (39 %, including sequences related to the pathogenic genus Francisella), and alpha-proteobacterial (30 %) sequences. Analysis of the Pfam domain family and Gene Ontology term variation revealed that the most frequent terms that appear unique to this consortium correspond to proteins involved in “transmembrane transporter activity” and “oxidoreductase activity”. Furthermore, we identified genes that encode for enzymes involved in the catabolism of complex substance for energy reserves. We also characterized members of the transposase and integrase superfamilies, whose role in bacterial evolution is well documented, as well as putative antifreeze proteins. Antibiotic treatments of E. focardii cultures delayed the cell division of the ciliate. To conclude, our results indicate that this consortium is largely represented by bacteria derived from the original Antarctic sample and may contribute to the survival of E. focardii in laboratory condition. Furthermore, our results suggest that these bacteria may have a more general role in E. focardii survival in its natural cold and oxidative environment.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-015-0568-9) contains supplementary material, which is available to authorized users.

Highlights

The Antarctic polar region represents a natural laboratory for evolutionary ecology studies
We report the characterization of the bacterial consortium associated to a long-term stabilized culture of the psychrophilic ciliate E. focardii, a species endemic of the Antarctic coastal seawaters [15]
In the last years, several studies on ciliate-bacteria associations focused on the characterization of bacterial symbionts of ciliates [6, 61–64], but in no cases, a detailed analysis of the microbial consortium associated to cultured cells were performed

Summary

Introduction

The Antarctic polar region represents a natural laboratory for evolutionary ecology studies. The cold but thermally stable seawaters of the Southern Ocean offer a large source of microbial ecosystems useful for exploring speciation and evolution with limited phenomena of gene flow from outside biota This is due to the geographical isolation of the Antarctic continent since its separation from Gondwanaland and the formation of the Polar Front 25 mya ago [1]. Ciliates living in an anaerobic habitat recurrently harbor hydrogen-consuming-bacteria that can use hydrogen as their main and vital substrate [7, 8]. Whether these bacteria have a key role in environmental adaptation and/or in enhancing the fitness of the host is not well established [7]. Even though some associations appear to be obligatory for both ciliates and bacteria, others may be ecologically advantageous but not vital for the host organism [9, 10]

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