Bentonite clay is the primary candidate for buffer material in a deep geological repository for high level nuclear waste in many countries. However, the material is only suitable if the swelling capacity is maintained with respect to changing temperature and humidity, as well as the possible impact of infiltrating fluids and/or microorganisms. Therefore, it is key to investigate possible influences that may change the swelling capacity of bentonite. This dataset was used to analyze the interaction between Wyoming bentonite clay (MX-80) and the bacterial strain Stenotrophomonas bentonitica BII-R7T (DSM 103927) under the influence of solutions of different salinities (NaCl, artificial Opalinus Clay porewater, and deionized water). The swelling capacity of the Na-montmorillonite was examined at temperatures between 27°C and 80°C, and relative humidity ranging from 0% to 80%.