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:Most recently, we identified 361 propionylation sites in 183 mid-exponential and late stationary phase proteins in Thermus thermophilus, an extremely thermophilic eubacterium (Okanishi et al. 2014), which was the first report showing the prevalence of post-translational lysine propionylation on diverse proteins.
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