Chapter 4, Problem 1DID

The genus Ferroplasma consists of a few species of acid-loving archaea. One species, F. acidarmanus, was discovered to be the main component of slime streamers (a type of biofilm) deep inside an abandoned California copper mine (Figure 4.11A).

F. acidarmanus cells use an ancient energy-harvesting pathway that combines oxygen with iron–sulfur compounds in minerals such as pyrite. This reaction dissolves the minerals, so groundwater that seeps into the mine ends up with extremely high concentrations of metal ions such as copper, zinc, cadmium, and arsenic. The reaction also produces sulfuric acid, which lowers the pH of the water around the cells to zero.

Despite living in an environment with a composition similar to hot battery acid, F. acidarmanus cells maintain their internal pH at a cozy 5.0. Thus, researchers investigating Ferroplasma metabolic enzymes were surprised to discover that most of the cells’ enzymes function best at very low pH (Figure 4.11B).

A. Deep inside one of the most toxic sites in the United States: Iron Mountain Mine, in California. The water in this stream, which is about 1 meter (3 feet) wide in this photo, is hot (around 40°C, or 104°F), heavily laden with arsenic and other toxic metals, and has a pH of zero. Slime streamers growing in it are a biofilm dominated by a species of archaea, Ferroplasma acidarmanus.

B. pH profiles of four enzymes isolated from F. acidarmus. Researchers had expected these enzymes to function best at the cells’ cytoplasmic pH (5.0).

What does the dashed line signify?