The crewed journey to Mars and its implications for the human microbiome

Abstract

A human spaceflight to Mars is scheduled for the next decade. In preparation for this unmatched endeavor, a plethora of challenges must be faced prior to the actual journey to Mars. Mission success will depend on the health of its crew and its working capacity. Hence, the journey to Mars will also depend on the microbiome and its far-reaching effects on individual crew health, the spaceship's integrity, and food supply. As human beings rely on their microbiome, these microbes are essential and should be managed to ensure their beneficial effects outweigh potential risks. In this commentary, we focus on the current state of knowledge regarding a healthy (gut) microbiome of space travelers based on research from the International Space Station and simulation experiments on Earth. We further indicate essential knowledge gaps of microbial conditions during long-term space missions in isolated confined space habitats or outposts and give detailed recommendations for microbial monitoring during pre-flight, in-flight, and post-flight. Finally, the conclusion outlines open questions and aspects of space traveler's health beyond the scope of this commentary. Video Abstract.

Keywords: Astronauts; Diversity; Gut; Healthy; Perturbation; Planetary protection; Reconstitution; Space; Space traveler; Spacecraft.

Fig. 1

Schedule of proposed microbiome monitoring on the journey to Mars. Shown is the schedule for switching from regular food (x1a) to space food (x1b), mobility of the astronauts (free or quarantine – beginning in x2), gravity (Earth = 1 g, Mars = 0.38 g, and space is 0 g), microbiome monitoring frequency (high, medium and low), and monitoring adjustment in case of an emergency (emergency in x6 leading to x6b). Sampling frequency phases are numbered sequentially (x1–x17) throughout the process and contain the following rationale: maintaining a low sampling frequency during flight to and from Mars (x6, x6d, and x13); switching to medium frequency after familiarization on Mars (x9), after lift-off from Mars (x12) or after landing back on Earth (x16); and high-frequency phases shortly before and after landing on and lift-off from Mars (x7, x8, x10, x11), before returning to Earth (x14), the first month back on Earth (x15), or whenever there is an incident involving the astronauts’ gut microbiome (x6b)