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:…2009; Volkers et al., 2010), transposition of insertion sequences has been associated with adaptation towards high physiological stress in E. coli, such as osmolarity (Stoebel et al., 2009), metal-limiting conditions (Chou et al., 2009) and nutrient limiting conditions (Gaff e et al., 2011).
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