Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…that only Fe2+bound form, but not Mn2+-bound form, of PerRBL senses low levels of H2O2, those genes (katA, ahpC, mrgA, and possibly pfeT) belonging to H2O2 stimulon are likely to be controlled by Fe2+-bound form of PerRBL, as previously known for B. subtilis PerR regulon (Fuangthong et al., 2002).
Category: