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Stanford University School of Medicine

Dolphins: The final frontier for new types of bacteria?

When a dolphin grins at you, he's also showing off the diverse community of microorganisms living on his teeth. Of course, you can't see those tiny critters with the naked eye.

That's where David Relman, MD, comes in. Relman's lab recently detected two uncharacterized bacterial phyla residing in the mouths of dolphins. Their findings appear in Current Biology. A phylum is broad taxonomic category that groups together organisms that share a common ancestor. Identifying new phyla gives scientists a closer look at the bacterial family tree.

For over 10 years, Relman has studied the dolphin microbiome in partnership with the U.S. Navy's Marine Mammal Program. The Marine Mammal Program reached out to Relman for help keeping its dolphins healthy. In return, Relman receives related microbes regularly.

(Fun fact: The U.S. Navy employs highly-trained dolphins to perform deep sea missions.)

Not unlike deep space or the ocean floor, dolphin innards are an alien environment to us - at least in terms of the bacteria found there. In particular, the dolphin mouth is home to surprising number of uncharacterized bacteria. Relman has a track record of uncovering unknown phyla, including some that had eluded detection for years. "Here we have this totally novel, ancient organism that has not been seen anywhere on the planet before, and we find it in a dolphin," said Relman.

To spot these microorganisms, Relman's lab analyzes swab samples from dolphin mouths to look at their genomes. Team members use a number of methods to collect and assemble DNA sequences into a complete genome. By comparing genomes, they can differentiate between different bacterial lineages.

By looking at the genes encoded in their genomes, the researchers can also predict how the new bacteria might behave. Genetic differences are also likely to correspond to differences in behavior, Relman said. For example, large insertions in one newly discovered phylum's genome give rise to unusual Cas9 proteins, of CRISPR-Cas9 fame, Relman explained in the study's news article:

Typically, people are interested in small Cas9 proteins that might be easy to manipulate and deliver into cells... These are the opposite -- they're enormously big.' Different structures in the genes that encode these proteins account for the size difference, and the researchers suggest these large Cas9 proteins have different properties from those known before.

Exploring these differences may give scientists insight into how marine mammals adapted to life in the ocean, as well as appreciation for the breadth of bacterial diversity on Earth.

Previously: Unknown bugs dominate the human microbiome and Stanford researchers discover new bacteria in dolphins
Photo by werdepate

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