Acknowledgements
This research was funded by grants DE-FG02-06ER64184 and ER64172-1027487-001191 from the Environmental Remediation Science Program, Office of Biological and Environmental Research, U.S. Department of Energy; by grants 0810190 and 0819954 from the National Science Foundation; and by financial support from the Office of Vice President for Research, University of Oregon. We thank the five reviewers for their constructive comments that significantly improved the quality of our manuscript.