Transcriptional and Proteomic Responses of<i>Pseudomonas aeruginosa</i>PAO1 to Spaceflight Conditions Involve Hfq Regulation and Reveal a Role for Oxygen

<jats:title>ABSTRACT</jats:title><jats:p>Assessing bacterial behavior in microgravity is important for risk assessment and prevention of infectious diseases during spaceflight missions. Furthermore, this research field allows the unveiling of novel connections between low-fluid-shear regions encountered by pathogens during their natural infection process and bacterial virulence. This study is the first to characterize the spaceflight-induced global transcriptional and proteomic responses of<jats:italic>Pseudomonas aeruginosa</jats:italic>, an opportunistic pathogen that is present in the space habitat.<jats:italic>P. aeruginosa</jats:italic>responded to spaceflight conditions through differential regulation of 167 genes and 28 proteins, with Hfq as a global transcriptional regulator. Since Hfq was also differentially regulated in spaceflight-grown<jats:italic>Salmonella enterica</jats:italic>serovar Typhimurium, Hfq represents the first spaceflight-induced regulator acting across bacterial species. The major<jats:italic>P. aeruginosa</jats:italic>virulence-related genes induced in spaceflight were the<jats:italic>lecA</jats:italic>and<jats:italic>lecB</jats:italic>lectin genes and the gene for rhamnosyltransferase (<jats:italic>rhlA</jats:italic>), which is involved in rhamnolipid production. The transcriptional response of spaceflight-grown<jats:italic>P. aeruginosa</jats:italic>was compared with our previous data for this organism grown in microgravity analogue conditions using the rotating wall vessel (RWV) bioreactor. Interesting similarities were observed, including, among others, similarities with regard to Hfq regulation and oxygen metabolism. While RWV-grown<jats:italic>P. aeruginosa</jats:italic>mainly induced genes involved in microaerophilic metabolism,<jats:italic>P. aeruginosa</jats:italic>cultured in spaceflight presumably adopted an anaerobic mode of growth, in which denitrification was most prominent. Whether the observed changes in pathogenesis-related gene expression in response to spaceflight culture could lead to an alteration of virulence in<jats:italic>P. aeruginosa</jats:italic>remains to be determined and will be important for infectious disease risk assessment and prevention, both during spaceflight missions and for the general public.</jats:p>