We have investigated the possibility of bacterial symbiosis in Globigerina bulloides, a palaeoceanographically important planktonic foraminifera commonly used in investigations of climatically sensitive sub-polar and temperate water masses and wind driven upwelling regions of the world’s oceans. G. bulloides is unusual, since it lacks the protist algal symbionts often found in other spinose species and has an atypical geochemical shell signature. This is suggestive of a divergent ecology, making it a good candidate for investigating potential bacterial symbiosis as a contributory factor in shell calcification. Such ecological information is essential to fully evaluate the potential response of G. bulloides to ocean acidification and climate change.