Space flight alters bacterial gene expression and virulence and reveals a role for global regulator Hfq

Abstract

A comprehensive analysis of both the molecular genetic and phenotypic responses of any organism to the space flight environment has never been accomplished because of significant technological and logistical hurdles. Moreover, the effects of space flight on microbial pathogenicity and associated infectious disease risks have not been studied. The bacterial pathogen Salmonella typhimurium was grown aboard Space Shuttle mission STS-115 and compared with identical ground control cultures. Global microarray and proteomic analyses revealed that 167 transcripts and 73 proteins changed expression with the conserved RNA-binding protein Hfq identified as a likely global regulator involved in the response to this environment. Hfq involvement was confirmed with a ground-based microgravity culture model. Space flight samples exhibited enhanced virulence in a murine infection model and extracellular matrix accumulation consistent with a biofilm. Strategies to target Hfq and related regulators could potentially decrease infectious disease risks during space flight missions and provide novel therapeutic options on Earth.

Fig. 1.

Data from STS-115 S. typhimurium experiments. (A) Map of the 4.8-Mb circular S. typhimurium genome with the locations of the genes belonging to the space flight transcriptional stimulon indicated as black hash marks. (B) Decreased time to death in mice infected with flight S. typhimurium as compared with identical ground controls. Female BALB/c mice per-orally infected with 10⁷ bacteria from either space flight or ground cultures were monitored every 6–12 h over a 30-day period, and the percent survival of the mice in each group is graphed versus the number of days. (C) Increased percent mortality of mice infected with space flight cultures across a range of infection dosages. Groups of mice were infected with increasing dosages of bacteria from space flight and ground cultures and monitored for survival over 30 days. The percent mortality (calculated as in ref. 23) of each dosage group is graphed versus the dosage amount. (D) Decreased LD₅₀ value (calculated as in ref. 23) for space flight bacteria in a murine infection model. (E) SEM of space flight and ground S. typhimurium bacteria showing the formation of an extracellular matrix and associated cellular aggregation of space flight cells. (Magnification: ×3,500.)

Fig. 2.

Hfq is required for S. typhimurium LSMMG-induced phenotypes in RWV culture. (A) The survival ratio of WT and isogenic hfq, hfq 3′Cm, and invA mutant strains in acid stress after RWV culture in the LSMMG and 1 × g positions is plotted (P < 0.05, ANOVA). (B) Fold intracellular replication of S. typhimurium strains hfq 3′Cm and Δhfq in J774 macrophages after RWV culture as above. Intracellular bacteria were quantitated at 2 h and 24 h after infection, and the fold increase in bacterial numbers between those two time periods was calculated (P < 0.05, ANOVA).