A considerable fraction of life develops in the sea at temperatures lower than 15 degrees C. Little is known about the adaptive features selected under those conditions. We present the analysis of the genome sequence of the fast growing Antarctica bacterium Pseudoalteromonas haloplanktis TAC125. We find that it copes with the increased solubility of oxygen at low temperature by multiplying dioxygen scavenging while deleting whole pathways producing reactive oxygen species. Dioxygen-consuming lipid desaturases achieve both protection against oxygen and synthesis of lipids making the membrane fluid. A remarkable strategy for avoidance of reactive oxygen species generation is developed by P. haloplanktis, with elimination of the ubiquitous molybdopterin-dependent metabolism. The P. haloplanktis proteome reveals a concerted amino acid usage bias specific to psychrophiles, consistently appearing apt to accommodate asparagine, a residue prone to make proteins age. Adding to its originality, P. haloplanktis further differs from its marine counterparts with recruitment of a plasmid origin of replication for its second chromosome.