Integrated physiological characteristics and proteomes of Bacillus licheniformis response to 6-month spaceflight.

Bacillus licheniformis (BL) is used for clinical treatment of acute and chronic enteritis and diarrhea. The present study explored the physiological characteristics and proteomes of BL response to 6-month spaceflight aboard the China Space Station. 6-month spaceflight delayed BL lag phase, reduced cell wall thickness, and impaired BL biofilm formation and adhesion capacity to Caco-2 cells. After 6-month spaceflight, activity of β-amylase, alkaline protease and lipase in BL was increased by 21.6%,67.3% and 42.5%. The alkaline resistance of BL at pH 11.0 was increased by 29.6%. Proteomics identified 6051 proteins in the BL. Of these, 62 of differentially abundant proteins (DAPs) groups were screened based on fold change (FC) > 1.5 and < 0.667 (P < 0.05). Thirty-six DAP groups exhibited an up-regulation trend with the maximum FC reaching 9.53. Twenty-six DAP groups were down-regulated. The molecular functions of DAPs were mainly classified into the transport of nutrients and ions, cell wall biosynthesis, mRNA metabolism and protein translation. These results revealed that 6-month spaceflight led to notably changes of physiological characteristics and proteins in BL. The novel findings may supply new insights into BL response to long-term complex space environment. SIGNIFICANCE OF STUDY: Complex space environment could lead to gastrointestinal system disorders of astronauts and enhance the risk of intestinal infections. BL, a Gram-positive probiotic bacterium, has potential to protect intestinal health of astronauts. To date, space microbiology studies on probiotic Gram-positive bacteria is rather limited. Physiological properties of BL onboard spaceflight missions are still lacking. The effect of long-term spaceflight on proteomes of BL has not been reported. The functional changes of DAPs in BL exposed to complex space environment remains unelucidated. Thus, it is urgent to carry out comprehensive study on spaceflight-BL. The purpose of present study was to explore the physiological characteristics and proteomic changes in BL abord the Shenzhou-15 spaceship into the China Space Station for 6 months. The novel findings are helpful to understand the response patterns of BL to spaceflight and provide a scientific support for the intestinal health protection of astronauts and the in-orbit application of this probiotic.