The mysterious and diverse world of bacteria just got its very own expansion pack. A total of 35 new groups, or phyla, of bacteria have been discovered in groundwater in Rifle, Colorado. The finding will likely add a bunch of new species to the tree of life — species that are quite different from other bacteria, scientists note. But here's what's really remarkable: the number of new bacterial groups is almost the same as the number of known animal phyla on Earth. We were always outnumbered, but you still might want to let the magnitude of this discovery sink in.

The number of bacterial groups discovered represent about 15 percent of the total number of bacteria that we’ve documented so far, says Jill Banfield, a geomicrobiologist at the University of California-Berkeley and a co-author of the study, published today in Nature. This "represents a substantial modification of the tree of life."

In the study, researchers used very fine filters to capture microorganisms in groundwater at a remediation site in Rifle, Colorado. The filters' holes were so fine that the scientists were able to capture bacteria that are about 400 nanometers across — microorganisms that normally pass through the kinds of filters we use to sterilize water.

Then, the scientists analyzed the samples. Thanks to the DNA they gathered, they found brand-new genomes — eight complete and 789 near-complete. But the 797 new genomes don't necessarily mean that many new species. "Each genome comes from one organism, but some of the genomes are so close to each other that you probably wouldn’t say that they were different bacteria," Banfield says. Still, the diversity uncovered by the researchers is substantial, especially if you think about how long these organisms have gone unnoticed.

"These [lineages] evaded more than 130 years of microbial cultivation studies," says Brian Hedlund, a microbiologist at the University of Nevada-Las Vegas, who didn’t participate in the study. "I think this work is incredibly exciting."

Credit: Banfield group graphic

Banfield and her team had suspected they might find new bacteria — but they weren't expecting this level of diversity. And the fact that these organisms are so different from other known species is intriguing. The bacteria have very small genomes and unusual genetic features, Banfield says. They also seem to lack the kinds of metabolic pathways that are usually required for independent growth, meaning that they need the help of other bacteria to survive. But the researchers don't know much more than that at the moment; characterizing these organisms, as well as their relationships with other bacteria, will take some time.

"Because these organisms are unusual and very distantly related to the organisms that have been studied in the lab, a large fraction of the genes encoded by their genomes remain enigmatic," Banfield says.

"The paper provided a very good accounting of genes that may be important for the physiology of these organisms," Hedlund says, "but in reality we have a long way to go before we will deeply understand the nature of these microorganisms, how they make a living, how they impact their symbionts, and their ecosystem more broadly."