99 percent of microbes in your body are completely unknown to science

From the abstract: "Analyzing cumulative sequence data from 1,351 blood samples collected from 188 patients enabled us to assemble 7,190 contiguous regions (contigs) larger than 1 kbp, of which 3,761 are novel with little or no sequence homology in any existing databases. "

I don't understand where the "99%" figure in the article comes from.