Microbial responses to microgravity and consequences for plant-microbe interactions in space

Bacteria and fungi inhabit most ecological niches on Earth and play essential roles in ecosystems, host health, and agricultural productivity. Recent progress in high-throughput technologies, together with the growing interest in establishing extraterrestrial colonies, has intensified efforts to understand how space-like environmental conditions affect living organisms. Yet, despite the ubiquity of microbes and their well-studied positive and negative impacts on plant and animal health, the effects of reduced gravity on microbial physiology remain underexplored. In this review, we synthesize findings from 61 published studies covering 55 different microbial species to evaluate how true and simulated microgravity influence bacterial and fungal growth, secondary metabolite production, stress resistance, biofilm formation and their symbiotic interaction with a host. Across these studies, microbial responses to microgravity were highly heterogeneous and trait-dependent. Our analysis revealed that species identity accounted for up to 48.8% of the variance in host colonization and 33.6% in growth, but had no significant effect on stress resistance and biofilm formation. Likewise, neither growth medium composition nor the microgravity-simulating platform significantly influenced any of the evaluated traits. Together, these results suggest microbial responses are driven primarily by species-specific genetic determinants rather than by a universal response to microgravity. These observations underscore that microbial behavior cannot be accurately predicted using simplified models, but must instead be interpreted in the context of each organism’s genomic background and the experimental conditions under which it is studied. They also emphasize the need for standardized experimental protocols and the expanded use of next-generation sequencing technologies such as transcriptomics, proteomics, or metabolomics to enable cross-study comparisons. These advances will be essential for understanding microbial adaptation in extraterrestrial environments and for exploiting bacterial and fungal functions in future space habitats.