AIM 1: CHARACTERIZE THE EFFECT OF SPACEFLIGHT ANALOGUE CULTURE ON MICROBIAL PATHOGENESIS RELATED STRESS RESPONSES AND IN VITRO HOST-PATHOGEN INTERACTIONS. ANALYSIS WILL INCLUDE MICROBIAL STRESS RESPONSES AS WELL AS COLONIZATION AND VIABILITY FOLLOWING PATHOGEN CHALLENGE OF THREE-DIMENSIONAL (3-D) TISSUE CO-CULTURE MODELS CONTAINING IMMUNE CELLS. AIM 2: CHARACTERIZE THE EFFECT OF SPACEFLIGHT ANALOGUE CULTURE ON THE VIRULENCE POTENTIAL OF PATHOGENIC MICROORGANISMS. CHANGES IN VIRULENCE WILL BE ASSESSED USING A MOUSE MODEL OF INFECTION. TO REDUCE AND REFINE THE USE OF ANIMALS FOR VIRULENCE STUDIES THE SELECTION OF MICROORGANISMS FOR AIM 2 WILL BE BASED ON A COMBINATION OF MICROBIAL RESPONSES FROM AIM 1 AND PREVIOUSLY REPORTED SPACEFLIGHT AND SPACEFLIGHT ANALOGUE EXPERIMENTAL DATA OF SIMILAR MICROORGANISMS.