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:bioreactors belong to the genus Pseudomonas, either because of their natural growth or as a result of initial inoculation (Ergas et al. 1994, 1995; Mirpuri et al. 1997; Pedersen et al. 1997; Veir et al. 1996).
Category: