Bacterial spore morphology remains highly recognizable after exposure to simulated Enceladus and Europa surface conditions

Abstract

The subsurface oceans of Enceladus and Europa are thought to be some of the best candidate environments for finding life beyond Earth. Realistically, the first missions aimed at searching for life on these worlds will likely be restricted to the shallow subsurface. Here, we investigated whether indicators of life, or biosignatures, deposited near the surface could persist long enough to be detected, given that the extremely harsh conditions there would tend to degrade them. We exposed Bacillus subtilis spores to Ocean World surface conditions and used electron microscopy combined with spectroscopic approaches to assess the preservation potential of structural and morphological biosignatures derived from spores. Our results show that spore structure is highly resilient in the face of extreme conditions long after they have been inactivated, suggesting that methods targeting cell morphology would be valuable components in a suite of life detection strategies used in future missions to Ocean Worlds. Experiments conducted at radiation and temperature conditions representative of the surfaces of Europa and Enceladus suggest the structure and morphology of bacterial spores remain intact despite loss of viability