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:Erwinia spp. produce the hydroxamate siderophore desferrioxamine E (Feistner et al. 1993; Kachadourian et al. 1996) and the specific TonB-dependent ferrioxamine receptor FoxR, both involved in iron uptake.
Category: