Understanding the limits of microbial life is one of the core questions in astrobiology. Microbial life rarely, if ever, exists as a single species on Earth, and more commonly exists as complex, mixed-species biofilms in many extreme environments. Biofilms, surface-attached microbial communities with a protective mucus layer that cells are encased in, provide protection from changing environmental conditions, and may preserve cells in some instances. In addition, within biofilms, microbes of different species can coordinate their metabolic activities through a process called quorum sensing (see Prescott and Decho 2020).
Such complex, highly interactive communities may be able to expand the limits of life, surviving multiple extreme conditions not possible by a single organism. This has direct implications for planetary protection, as humans move to other planetary bodies, and for upcoming missions to the Moon and Mars. Microbes will be both a threat and helpful assistants as we develop systems for sustaining human life off-world. Understanding these complex and cooperative interactions among microbes may also help us better understand how life evolved on Earth, and how it might evolve elsewhere, and the role of cooperative behavior in the evolution of life.
