Complete genome of Nocardioides aquaticus KCTC 9944T isolated from meromictic and hypersaline Ekho Lake, Antarctica

Abstract

Nocardioides aquaticus KCTC 9944T is an aerobic, non-motile, Gram-positive, psychrotolerant, non-spore-forming bacterium isolated from the surface water of Ekho Lake in the Vestfold Hills, East Antarctica. This meromictic lake separated from Antarctic seawater thousands of years ago exhibits steep gradients of salinity and temperature in the upper layer of the water column. The cells of N. aquaticus thriving in Ekho Lake are able to grow in wide ranges of temperature (3 to 43.5 °C) and salinity (0 to 15% NaCl). Here, we sequenced the complete genome of N. aquaticus KCTC 9944T, aiming to better understand the adaptation of this bacterium to the strong environmental gradients at the molecular level. The genome consists of 4,580,814 bp (G + C content of 73.2%) with a single chromosome, 4432 protein-coding genes, 51 tRNAs and 2 rRNA operons. The genome possesses genes for the Entner-Doudoroff pathway, photoheterotrophy, the conversion of acetate to acetyl-CoA, gluconeogenesis, and energy storage that are all advantageous to oligotrophic bacteria. The presence of genes involved in osmotic balance, fatty acid desaturation, cold and heat shock responses, and the oxygen affinities of respiratory oxidases are likely associated with high tolerance to strong gradients of salinity, temperature and oxygen concentration.