1. Department of Biological Sciences, University of Southern California, Los Angeles, California
2. Centro de Astrobiologia CSIC-INTA, Centra Torrejón a Ajalvir, Torrejón de Ardoz, Madrid, Spain
3. Biosciences Division, Argonne National Laboratory, Argonne, Illinois
4. Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama