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Catalase-negative bacteria may be anaerobes, or they may be facultative anaerobes that only ferment and do not respire using oxygen as a terminal electron acceptor
A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent
But if facultative anaerobes can be present in oxygen rich environments, don't they have to have catalase in order not to die?
There is another class of peroxide decomposing enzymes called peroxidases. These enzymes can catalyze the reduction of $\ce{H2O2}$ to water using an electron donor. However, unlike in the catalase reaction, the electron donor is not another $\ce{H2O2}$ molecule and no molecular oxygen is produced. Thus their presence would not be detected by the typical spot catalase test (which looks for gaseous oxygen generation). For example, NADH peroxidase catalyzes the following reaction to protect cells from oxidative damage:
$$\ce{NADH + H+ + H2O2 -> NAD+ + 2H2O}$$
Thus catalase negative organisms can still have a means of protection against $\ce{H2O2}$. You can read more in this textbook, specifically the section titled "Oxygen Toxicity".
