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:fumigatus encodes two transcription factors, hapX and sreA, that maintain iron homeostasis whereby hapX represses sreA expression and subsequently ironconsuming pathways, and activates siderophore biosynthesis during iron-starvation, while sreA represses hapX during iron-sufficient conditions in a negative feedback loop [35,56].
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