Microbial diversity formation and maintenance due to temporal niche differentiation caused by low-dose ionizing radiation in oligotrophic environments.

The planetary protection strives to minimize the contamination of microorganisms in spacecrafts. However, it is reported that microbial diversity is abnormally high in the International Space Station (ISS) after long-term exposure to low-dose ionizing radiation (LDIR). It remains a mystery why LDIR leads to the formation and maintenance of high microbial diversity in oligotrophic environments like the ISS. In this study, an artificial microbial community has been cultivated without and with LDIR, respectively. The microbial community was composed of three common microbial species, i.e., Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa in the ISS. After analyzing the differences in microbial physiological and behavioral response characteristics in the two scenarios, a reasonable hypothesis was proposed to elucidate the formation and maintenance mechanisms of high microbial diversity in oligotrophic environments with the LDIR. Then a set of kinetic models with time-lag were developed based on this hypothesis, observed phenomena, and experimental data. Finally, these kinetic models were sufficiently validated, and the hypothesis was fully confirmed through large-scale digital simulations. Briefly, as a decisive succession mechanism in oligotrophic environments with LDIR, temporal niche differentiation (TND) caused by microbial delayed responses to LDIR can give rise to asynchronously convergent fluctuations of microbial populations and significantly alleviate the intra- and interspecific competitions. Such a mechanism can drive the microbial communities in oligotrophic environments with LDIR to form and maintain high species diversity.