Carbonates’ precipitation by halophilic bacteria as a potential biosignature for the search for life on Mars

Abstract

The mechanisms of Mg-carbonate precipitation in the Earth's modern sedimentary environments has not yet been completely elucidated. However, it is known that the microbial activity is significant to facilitate or induce mineral formation. The organic EPS matrix secreted by microorganisms provide an ideal physicochemical environment to the mineral nucleation. Sediments and water samples were collected at Lagoa Vermelha, Araruama (RJ), Brazil. This lagoon is characterized of being a hypersaline lake, where we can find a range of microorganisms known as halophilic and halotolerant extremophiles that have adaptation strategies to compensate for the harmful effects of high salinity, such as EPS biosynthesis, which is one of the most common protection mechanisms in bacteria, helping to maintain the integrity of their cells’membrane. In the present project, the bacterial capability of bioprecipitation using bacterial isolates from a hypersaline lagoon was investigated by combining microbiological, microscopic and geochemical analytical techniques. The isolates were evaluated for their ability to produce bioprecipitates using this multi-technique approach that includes Scanning Electron Microscopy (SEM) with EDS, XRD and Raman spectroscopy. It was possible to characterize the carbonates formed by the bacteria isolated. Finally, these carbonates could represent a potential target for astrobiological studies of potential potential biosignatures for the search for life beyond Earth.