Research About The Impact Of Twice Spaceflight On The Bacillus Cereus

The manned space flight has been becoming the hot spot for the study gradually, which come up with the new theme and challenge for the study of the space life science and medical science. Under the microgravity condition in the space, human being’s immune function will be affected and even suffer some defects, during which, various opportunistic pathogens, including the bacteria, fungus and virus, will invade human body by making full use of the weak body immune function, in order to cause seriously infectious diseases. Meanwhile, there is remarkable difference between the pathogens in the space condition and the regular bacteria strain in the ground in terms of the pathogenic mechanism and drug tolerance, since the microgravity may affect the bacterial growth momentum, bacterial cell behavior and bacterial genotype. Therefore, it is urgent to study the variation of the strain in the space flight clearly, and design the brand-new diagnosis, prevention and treatment regimens aiming at its pathogenic mechanism and drug tolerance phenotype. in order to cope with the bacterial infection encountered in the long-term outer space expedition.The bacillus cereus is gram-positive bacteria that is a kind of conditionally pathogenic bacteria, which is one of the most common food borne pathogens, as well as one of the significant pathogens that cause human being suffer the infectious diseases, and it can almost infect all kinds of foods, and generate three kinds of different enterotoxin and cause vomiting syndrome and diarrhea. The space stations have widespread the bacillus cereus to which the foods of the astronauts are vulnerable. Therefore, the study on the bacillus cereus mutated in the space is significant for the astronauts and the personnel in the space. The early study in this research group discovers a series of differential phenotypes by the analysis on the genome, transcriptome and proteome after delivering the bacillus cereus into the space in the spacecraft Shenzhou 8. This project re-delivers the bacillus cereus LCT-BC25 mutated after the space flight into the space with the spacecraft Shenzhou 10, in order to study the impact to the strain by the space flight in different durations.This study is divided into two parts, (1) the induction implementation of the bacillus cereus in the secondary space environment; (2) the impact to the bacillus cereus by the secondary space flight.Part Ⅰ:the induction implementation of the bacillus cereus in the secondary space environmentIn this part, the little carrying tube and outside packing tube made of polycarbonate were used to carry LCT-BC25 and control bacteria into the space and recycled, and the PCR was used to expand 16S rDNA to identify the bacillus cereus induced by the secondary space environment, with the homologous analysis and the evolutionary analysis for the single bacteria. The results indicate that there is 99% similarity between the bacillus cereus LCT-BC25 induced by the secondary space environment and the bacillus cereus ATCC 14579(T), with stable properties unchanged, which can be further used into the next experiment and study, but longer space environment will more inhibited the proliferation of the Bacillus cereus.Part Ⅱ:the impact to the bacillus cereus by the secondary space flightAs the key, this part will make the phenotype analysis on the bacteria strain LCT-BC25-2 in the secondary space flight, the bacteria strain LCT-BC25-1 in the primary space flight and the ground control bacteria strain LCT-BC244 in terms of the colony proliferation, drug tolerance and toxicity etc, and conduct differential gene analysis using genome and transcriptome sequence. The experimental results indicate that the secondary space flight will weaken the proliferation ability of the bacillus cereus, and decrease its ability to proliferate its tissues. The combination of genome sequence, PCR and western blot verification indicate that there is a series of drug tolerance genes and toxic genes with differential expressions.Of which, there is remarkably high expression of vanG similar genes in the bacteria LCT-BC25-2 in the secondary space flight. After the vanG was overly expressed in the strain LCT-BC25-1 in the primary space flight and the strain LCT-BC244 in the ground control strain using the method of gene transformation, it is discovered that the upward floating drift of MIC value of the vancomycin both happened for the two, which indicated that the appearance of vanG similar genes is one of key factors contributing to the upward floating drift of MIC value of the vancomycin; there is remarkably low expression of pagA similar genes in the strain LCT-BC25-2 of the secondary space flight, and the strain LCT-BC25-2 of the over expression pagA recovered the cell toxicity to the mouse, which indicated that the low expression of pagA was one of key factors to weaken the toxicity caused by the secondary space flight. Cell Based test indicating that lower density of pagA caused by the secondary space flight might block the bacillus cereus from activating the host ERK pathway, and therefore make the strain deficient of toxicity and Inflammatory ability.Conclusion:1) It is discovered that the secondary space flight,which expose the bacillus cereus in the outspace longer than the first time space flight, decreases the proliferation ability of the bacillus cereus,with its drug tolerance status changed and there is upward floating drift of MIC value of the vancomycin. The acute and chronic toxicity to the mouse from the bacillus cereus and the proliferation ability in the organism are weakened.2) It is discovered that the alternation of the some drug resistant related genes and virlence related genes are the key factors of MIC up-drift for vancomycin and decreased toxicity of the strains caused by secondary space flight.3) It is discovered that the appearance of the vanG similar gene is one of the key factors that the MIC value of the bacillus cereus has upward floating drift to the vancomycin; it is discovered that the decrease of pagA similar gene expression is one of the key factors that the toxicity of the bacillus cereus is decreased in the secondary space flight. Mechanism of pagA on the virulence of strains might be that it interact the TLR receptor and regulated the downstream ERK expression.4) It is discovered that the long-term microgravity environment is the key factory that causes the change of vanG similar gene and pagA simiar gene of the bacillus cereus, which results the change of drug tolerance phenotype and toxicity phenotype of the bacteria strain.