Comment by mlu

This is the result what one would expect. Scientists (until recently) have only been able to sequence species which can be cultured in the laboratory (you need massive amounts of DNA for sequencing). But in fact, more than 90 percent of all microbial species cannot be cultured in the lab and hence (until recently) could not be sequenced and stayed unknown. However, in the past few years, "Next next generation sequencing" (that's how I like to call it) techniques emerged and we are now able to sequence nearly everything. The umbrella terms "metagenomics" and "single-cell sequencing" are often used for such new methods and have huuuge potential in many, many fields. Basically, the new methods eliminate the culturing step and instead have novel techniques for amplifying DNA from only a single strand.