Do strictly anaerobic organisms use metabolic reactions requiring oxygen?
Strict anaerobes do not use molecular oxygen for oxidation reactions.

The oxidation of ferrous iron to ferric iron (viz. the example given by Septimus G) can be done anaerobically by anaerobic purple bacteria [eq. 2 in Ehrenreich &amp; Widdel (1994) Appl Environ Microbiol 60: 4517-4526]:

4 FeCO3 + 10 H20 --&gt; 4 Fe(OH)3 + (CH20) + 3 HCO3- + 3 H+


https://www.ncbi.nlm.nih.gov/pubmed/7811087