Which of the following types of bacteria requires increased carbon dioxide for optimal growth?

Bacteria that require increased carbon dioxide for optimal growth are referred to as capnophiles. These organisms thrive in environments where carbon dioxide concentrations are higher than what is normally found in the atmosphere, typically around 5-10% CO2, compared to the atmospheric level of about 0.03%. The increased carbon dioxide can be crucial for their metabolic processes, influencing factors such as respiration and fermentation.

Microaerophiles are a category of bacteria that require reduced levels of oxygen (typically around 2-10%) for growth and may not necessarily prefer elevated levels of carbon dioxide. Anaerobes are organisms that do not require oxygen for growth, and while some may tolerate certain carbon dioxide levels, they primarily thrive in environments devoid of oxygen. Facultative anaerobes can grow in both the presence and absence of oxygen and can adapt their metabolism accordingly but do not specifically require high carbon dioxide concentrations for optimal growth.

Thus, the defining characteristic of capnophiles makes them the correct answer, as they specifically flourish in higher levels of carbon dioxide, contrasting with the requirements of the other bacterial types mentioned.