Anaerobic respiration is simply respiration in the ABSENCE OF OXYGEN.
A positive nitrate test mean Escherichia coli reduces NO3 (Nitrate) to NO2 (Nitrite). This is based on its ability to produce nitrate reductase enzyme that catalyze the reduction process. And note that this reaction occurs in the ABSENCE OF OXYGEN.
This makes E. coli an ANAEROBE ( an organism that can survive in the absence of oxygen)
