Chapter 5, Problem 2DAA

One Tough Bug The genus Ferroplasma consists of a few species or acid-loving archaea. One species, F. acidarmanus, was discovered to be the main constituent of slime streamers (a type of biofilm) deep inside- an abandoned California copper mine (FIGURE 5.36). These cells use an ancient energy-harvesting pathway that combines oxygen with iron-sulfur compounds in minerals such as pyrite. Oxidizing these minerals dissolves them, so groundwater that seeps in to 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.

F. acidarmanus cells maintain their internal pH at a cozy 5.0 despite living in an environment similar to hot battery acid. Thus, researchers investigating Ferroprasma were surprised to discover that most of the cells' enzymes function best at very low pH (FIGURE 5 .37).

FIGURE 5.36 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 view, is hot (around 40°C, or 104°F), heavily laden with arsenic and other toxic metals, and has a pH of zero. The slime streamers growing in it are a biofilm dominated by a species of archaea Ferropiasma acidarmanus.

FIGURE 5.37 pH anomaly of Ferroplasma acidarmanus enzymes. The graphs (right) show the pH activity profiles of four enzymes isolated from Ferroplasma. Researchers had expected these enzymes to function best at the cells' cytoplasmic pH (5.0).

2. Of the four enzymes profiled in the graph, how many function optimally at a pH lower than 5? How many retain significant function at pH 5?