Actinobacteria-mediated serpentine dissolution and implication for biosignatures on Mars

Abstract

The search for traces of life is one of the principal objectives of Mars exploration. The global distribution of minerals associated with serpentinization in the Noachian terrains on Mars likely suggest that serpentinization commonly occurred early in the planets history. A consensus is that these reactions involved in the serpentinization may have provided the initial material and energy for the origin and early evolution of life on Earth. Comparably, the serpentine regions of Mars are potential target sites for the detection of the putative life on Mars. Herein, an actinobacterial species Streptomyces spp. FXJ8.102 is used as a model microbe to investigate the microbe-mediated dissolution of antigorite in liquid culture. The experimental results show that the strain can couple biomechanical and biochemical mechanisms in the serpentine dissolution, leading to the development of “cell-sized” and “cell-shaped” eroded pits/channels on the mineral surfaces, and the low Mg/Si ratios on the eroded sites. In addition, the cells can also induce the formation of secondary glushinskite during the dissolution process. By contrast, no distinguishable surface change on antigorite and secondary mineral formation can be observed in the control experiments without inoculation. Therefore, a collection of the features including the distinctive eroded texture and composition on serpentine surfaces, and the special mineral assemblage including the formation of secondary oxalate minerals may serve as a compelling biosignature for the search of life on Mars.