Proteobacteria are facultative anaerobes that tend to outcompete obligate anaerobes when oxygen is present, favoring aerobic metabolism.

“those are generally you said they're most of them they're gram-negative anaerobes uh facultative facultative anaerobes meaning meaning that they uh they tend to out-compete obligate anaerobics when there's oxygen present so they're but they're not and then they're not aerobes so they're not they're not gram-negative they're not anaerobic organisms or they're not aerobic organisms correct correct so they can they can basically either do anaerobic or aerobic metabolism metabolism even though they they tend towards anaerobic but if they're out if they're in the gut environment competing with other organisms and oxygen becomes present they tend to favor that aerobic metabolism to outcompete their neighbors right”