Candidate Phyla Radiation (CPR): Branch of bacteria announced only in 2015; represents about half of the domain’s diversity — and a third of the diversity of life on Earth.
Saccharibacteria: Only CPR member that has been successfully grown in isolation in a lab.
Lactobacillus: Probiotic also used to make yogurt and cheese.
Staphylococcus: Causes a common hospital-acquired infection.
Actinomyces odontolyticus: Found in the human mouth; hosts a parasitic CPR bacterium, TM7x, that has such a small genome it cannot synthesize amino acids on its own.
Chlamydia: Culprit of a common sexually transferred infection.
Leptospirillum: Bacterium found in acidic mine drainage; provides a habitat for other organisms that can only survive the harsh environment in its biofilm.
Helicobacter: Organism shown to cause stomach cancer.
E. coli and Salmonella: Causes of food poisoning.
Woesebacteria: Named after Carl Woese, who, based on his earlier work, created the first modern tree of life in 1990 by separating life into the three domains.
[This article originally appeared in print as "Tree of Life."]