Metabolism of metals in Antarctic endolytic bacteria

Dr. Elena Fabiano, Instituto de Investigaciones Biológicas Clemente Estable (IIBCE)

Although more than 80% of the volume of the biosphere is at temperatures below 4 ° C and most of the biomass is microbial, very little is known about the biology of microorganisms inhabiting permanently cold environments. Antarctica is the coldest and driest continent on Earth and suffers from extreme weather conditions including extremely low temperatures, low atmospheric humidity, low bioavailability of water, periods of high incidence of UV radiation and long periods of darkness. Despite this, microbial communities successfully survive in this environment, especially in the interior of the rocks. The microbial communities that inhabit the rocks are known as endolithic communities and it has been estimated that approximately 80% of the microbial population of the planet is endolithic. Endolithic microbial communities colonize cracks, pores, interstices, and fractures of rocks, and these niches can represent the main refuge for life in some extreme places of the planet. Microbes directly participate in the evolution of rocks, and may directly or indirectly alter their physical and chemical properties.

The objective of our work is directed to the characterization of the functional diversity of the microbes that inhabit the Antarctic rocks. In particular we focus on the study of bacterial systems involved in the maintenance of homeostasis of metals such as iron, nickel, zinc, manganese, copper, cobalt, silver. We are interested in determining the bacterial ability to produce pigments and to determine whether pigment production depends on metal tolerance.

Since 2011, our team has made regular incursions into Antarctica. While the campaigns have focused primarily on King George Island, we also prospect a site on the Antarctic peninsula. During the exploration tours, samples were collected from different niches, such as lake water, thawing water, glacier snow, sediments, microbial forests and also different types of rocks. Our studies focused on obtaining and analyzing cultivable bacteria and also obtaining total DNA from the bacterial community (metagenomic DNA), building functional metagenotecas and analyzing them. We have now identified different cultivable bacteria present in two samples of Antarctic rocks. Most of the isolated strains were Actinobacterias (Gram positive) and were related to the genera Arthrobacter and Mucilaginibacter and in smaller proportion Rhodococcus, Hymenobacter, Frigobacterium and Cryobacterium were found. Interestingly, many isolates showed low identity (96% or less) with sequences available in the public databases, which would reflect the novelty of these bacteria. We identified isolates capable of growing and producing functions related to metal transformation at 5 °C. Our current interest is to expand the collection of endolytic cultivable bacteria present in different types of rocks. We are also optimizing the protocols to construct functional metagenotecas and analyze the genetic information present in the bacterial DNA of the endolithic community.