A) Methanocaldococcus.
B) Halobacterium.
C) Methanococcus.
D) Thermoplasma.

A) produce methane as a part of their energy metabolism.
B) utilize methane as an energy source.
C) process and store methane to detoxify it.
D) produce, utilize, and detoxify methane.

A) primarily ancient organisms that have not evolved very much in the last billion years.
B) phylogenetically diverse, but functionally restricted to extremophiles and chemolithotrophs.
C) a group of diverse microorganisms that inhabit almost every environment on Earth, including the colon of humans and other mammals.
D) functionally diverse, but restricted to thermophilic or hyperthermophilic environments.