Influence mechanism of low-dose ionizing radiation on Escherichia coli DH5α population based on plasma theory and system dynamics simulation

Combined effect of simulated microgravity and low-dose ionizing radiation on structure and antibiotic resistance of a synthetic community model of bacteria isolated from spacecraft assembly room

Understanding the structural and antibiotic resistance changes of microbial communities in space environments is critical for identifying potential pathogens that may pose health risks to astronauts and for preventing and controlling microbial contamination. The research to date on microbes under simulated space factors has primarily been carried out on single bacterial species under the individual effects of microgravity or low-dose radiation. However, microgravity (MG) and low-dose ionizing radiation (LDIR) coexist in the actual spacecraft environment, and microorganisms coexist as communities in the spacecraft environment. Thus, the microbial response to the real changes present during space habitation has not been adequately explored. To address this knowledge gap, we compared the dynamics of community composition and antibiotic resistance of synthetic bacterial communities under simulated microgravit, low-dose ionizing radiation, and the conditions combined, as it occurs in spacecraft. To ensure representative bacteria were selected, we co-cultured of 12 bacterial strains isolated from spacecraft cleanrooms. We found that the weakened competition between communities increased the possibility of species coexistence, community diversity, and homogeneity. The number of Bacilli increased significantly, while different species under the combined conditions showed various changes in abundance compared to those under the individual conditions. The resistance of the synthetic community to penicillins increased significantly under low doses of ionizing radiation but did not change significantly under simulated microgravity or the combined conditions. The results of functional predictions revealed that antibiotic biosynthesis and resistance increased dramatically in the community under space environmental stress, which confirmed the results of the drug sensitivity assays. Our results show that combined space environmental factors exert different effects on the microbial community structure and antibiotic resistance, which provides new insights into our understanding of the mechanisms of evolution of microorganisms in spacecraft, and is relevant to effective microbial pollution prevention and control strategies.

Effects of Persimmon Tannin-Aloe vera Composite on Cytotoxic Activities, and Radioprotection Against X-rays Irradiated in Human Hepatoma and Hepatic Cells

A persimmon tannin-Aloe vera composite powder (PT-A) was investigated for its capacity to protect against ionizing radiation. Human hepatic cells (L02 cells) and human hepatoma cells (HepG2 cells) were pretreated with different concentrations of PT-A or the single compounds (PT or Aloe vera) and radiated with X-rays. After radiation and post-incubation for 12 h or 24 h, the cell viability, apoptosis, and reactive oxygen species (ROS) production were analyzed by Cell Counting Kit 8 (CCK-8), 2',7'-dichlorfluorescein diacetate (DCFH-DA) staining, and Hoechst 33258 staining/flow cytometry, respectively. CCK-8 results illustrated that the optimal radiation dose L02 cells was 8 Gy for L02 cells, and the cell activity was 71.72% (IC₅₀ = 412.1 μg/mL) after post-radiation incubation of 12 h. For HepG2 cells, the optimal radiation dose was 8 Gy, and the cell activity was 62.37% (IC₅₀ = 213.0 μg/mL). The cell apoptotic rate was the lowest at a PT-A concentration of 200 μg/mL in L02 cells (4.32%, P < 0.05), and at 100 μg/mL in HepG2 cells (9.80%, P < 0.05). ROS production induced by radiation could be effectively inhibited by 200 μg/mL of PT-A in L02 cells, and by 100 μg/mL of PT-A in HepG2 cells. The PT-A composite has good radioprotective effects on cell vitality and apoptosis of X-rays radiation exposure towards L02 cells and HepG2 cells compared to the persimmon tannin or Aloe vera. Therefore, PT-A composite might be useful as a natural, harmless anti-ionizing radiation agent, and has various clinical application prospects in future.