Updated 1 March 2012 Long-term exposure of bacterial cells to simulated microgravity Faithi Karouia* a , Madhan R. Tirumalit b , Mayra A. Nelman-Gonzalez c , Clarence F. Sams d , Mark C. Ott d , Richard C. Willson e , Duane L. Pierson d , George E. Fox b a NASA Ames Research Center, Foffett Field, CA, USA; b Dept. Biology & Biochemistry, University of Houston, 4800 Calhoun Road, Houston, TX, USA 77204-5001; c Wyle International Science and Engineering, Houston, TX, USA, d NASA Johnson Space Center, 2401 NASA Parkway, Houston, TX, USA 77058; e Dept Chemical & Biomolecular Engineering, University of Houston, 4800 Calhoun Road, Houston, TX, USA 77204-4004. ABSTRACT Previous space flight experience has demonstrated that microorganisms are just as ubiquitous in space habitats as they are on Earth. Numerous incidences of biofilm formation within space habitats have been reported; some of which were identified only after damage to spacecraft structures and irritation to astronaut’s skin occurred. As we increase the duration of spaceflight missions, it becomes legitimate to question the long-term effects of microgravity on bacteria. To begin this assessment, Escherichia coli K-12 strain MG1655 was grown for one thousand generations (1000G) under low shear modeled microgravity. Subsequently, growth kinetics and the presence of biofilm were assessed in the 1000G strain as compared to a strain (1G) briefly exposed to LSMMG. Overall, the analysis revealed that (i) there was no obvious difference in growth kinetics between the 1G and 1000G strains, and (ii) although biofilm formation was not seen in the 1G strain it did in fact occur as exposure time increased. The results suggest that long-term exposure to the space environment likely favors biofilm formation in many organisms. Keywords: microgravity, HARV, Low shear modeled microgravity, bacterial adaptation, Scanning electron microscopy INTRODUCTION Studies on board spacecraft, Apollo, Space Shuttle, Salyut, Mir, and the International Space Station (ISS), have shown the presence of a large variety of bacterial and fungal species. 1-8 Several opportunistic pathogenic organisms have been identified and emphasize that potential conditions for infectious outbreaks on future space missions remain a realistic concern. Space travelers, including bacteria, experience a unique environment that affects homeostasis and physiologic adaptation. Several conditions foster microbial contamination in the space environment, including the reduced living space and limited capabilities for personal hygiene and for disinfection of surfaces. Additionally, even the healthiest individual carries a large number of microorganisms, many of which are constantly shed into the environment, guaranteeing a constant source of anthropogenic contamination. Multiple short term spaceflight and low shear modeled microgravity (LSMMG) experiments have shown changes in phenotypic microbial characteristics such as microbial growth, morphology, metabolism, genetic transfer, antibiotics and stress susceptibility, virulence factors and biofilm formation. 9,10 . Biofilm formation is especially problematic. Bacteria have evolved elaborate mechanisms for adhering to and colonizing solid surfaces, thereby establishing microbial communities. 11 These sessible microbial communities formed on solid surfaces are ubiquitous in natural environments as well those associated with medicine and engineering. Due to their resistance to antimicrobial agents and antibiotics, biofilms can cause serious health problems such as endocarditis, cystic fibrosis, otisis media, and urinary tract infections. 12 It is estimated that biofilms are involved in 65% of human bacterial infections. Additionally biofilms can stimulate microbial induced corrosion on the surfaces of pipes, reduce the efficiency of heat exchangers, and cause food spoilage. 1