Low temperature is a critical factor controlling the evolution and biodiversity of life on Earth. Most (~85%) of the Earth’s biosphere is permanently below 5°C. In the Vestfold Hills, Antarctica, more than 3000 water bodies from freshwater (<0.1%) to hypersaline (32%) exist, many of which are marine-derived. In 2006 we commenced an environmental genomics and proteomics program and have learned about unanticipated and important roles for specific components of the microbial loop, and the apparent ‘peculiarities’ of polar ecosystems. For example, Ace Lake and Organic Lake revealed unexpected roles for viruses (e.g. virophages and phage resistant bacteria) and dominant cellular species (e.g. green sulfur bacteria), and Deep Lake an extraordinary level of inter-genera genetic exchange.
In this talk I will overview our ‘omic’-based discoveries and focus on haloarchaea in Deep Lake. By analysing metagenome data, and genome sequences of four Deep Lake isolates, we have analysed genome variation and patterns of gene exchange. The lake is completely and uniformly dominated by haloarchaea, which form a hierarchically structured, low complexity community that differs greatly to temperate and tropical hypersaline systems. Strikingly, the Antarctic haloarchaea were found to exhibit signatures of very high inter-genus gene exchange, with some of the shared DNA being long (up to 35 kb) and virtually 100% conserved. With extremely low cell division rates in the cold (–20°C), the remarkable extent of lateral exchange that has been demonstrated to occur could conceivably homogenize the population. It is therefore notable that different genera are maintained in the lake, and the ability of the phylogenetically distinct haloarchaea to coexist has been linked to genomic differences conferring ecotype distinctions that enable niche adaptation (sympatric speciation). The talk will summarise findings from two recent papers [1,2], and present new data (e.g. metaproteomics, proteomics and genetics).