Which type of bacteria are known to thrive in low-oxygen environments?

Anaerobic bacteria are the correct answer because these microorganisms are specifically adapted to live in environments with little to no oxygen. They utilize alternative pathways for metabolism, primarily fermentation or anaerobic respiration, which do not require oxygen. This adaptation allows them to thrive in diverse environments such as deep soils, sediments, and certain water bodies where oxygen levels are low.

In contrast, aerobic bacteria require oxygen for their growth and metabolic processes. Coliform bacteria, which are often used as indicators of water quality, can grow in both aerobic and anaerobic conditions but are not exclusively anaerobic. Pathogenic bacteria encompass a wide variety of bacteria that can cause disease, and while some may be anaerobic, they are not classified solely by their oxygen requirements. Thus, anaerobic bacteria's unique capability to flourish in low-oxygen settings distinguishes them clearly from these other types of bacteria.