Today, sugar has a villainous reputation. And while too much of the sweet stuff should be avoided, all living things need sugar to survive. “The biological universe is coated with sugars,” said Samuel M. Levi and Qiuhan Li, graduate students in Harvard University’s Department of Chemistry and Chemical Biology. “Cells, bacteria, viruses and other organisms use sugars as a means of communication, recognition, and even defense.” Nature literally runs on sugars.