Abstract
Biofilm formation is closely related to the pathogenetic processes of Klebsiella pneumoniae, which frequently causes infections in immunocompromised individuals. The immune system of astronauts is compromised in spaceflight. Accordingly, K. pneumoniae, which used to be isolated from orbiting spacecraft and astronauts, poses potential threats to the health of astronauts and mission security. Microgravity is a key environmental cue during spaceflight. Therefore, determining its effects on bacterial biofilm formation is necessary. In this study, K. pneumoniae ATCC BAA‐1705 was exposed to a simulated microgravity (SMG) environment. K. pneumoniae grown under SMG formed thicker biofilms compared with those under normal gravity (NG) control after 2 weeks of subculture. Two indicative dyes (i.e., Congo red and calcofluor) specifically binding to cellulose fibers and/or fimbriae were utilized to reconfirm the enhanced biofilm formation ability of K. pneumoniae grown under SMG. Further analysis showed that the biofilms formed by SMG‐treated K. pneumoniae were susceptible to cellulase digestion. Yeast cells mannose‐resistant agglutination by K. pneumoniae type 3 fimbriae was more obvious in the SMG group, which suggests that cellulose production and type 3 fimbriae expression in K. pneumoniae were both enhanced under the SMG condition. Transcriptomic analysis showed that 171 genes belonging to 15 functional categories were dysregulated in this organism exposed to the SMG conditions compared with those in the NG group, where the genes responsible for the type 3 fimbriae (mrkABCDF) and its regulator (mrkH) were upregulated.
Highlights
Several opportunistic bacterial pathogens have been detected in samples from human space habitats and postflight astronauts (Castro et al 2004; Novikova 2004)
Yeast cells mannose-resistant agglutination by K. pneumoniae type 3 fimbriae was more obvious in the simulated microgravity (SMG) group, which suggests that cellulose production and type 3 fimbriae expression in K. pneumoniae were both enhanced under the SMG condition
Transcriptomic analysis showed that 171 genes belonging to 15 functional categories were dysregulated in this organism exposed to the SMG conditions compared with those in the normal gravity (NG) group, where the genes responsible for the type 3 fimbriae and its regulator were upregulated
Summary
Several opportunistic bacterial pathogens have been detected in samples from human space habitats and postflight astronauts (Castro et al 2004; Novikova 2004). Microgravity is a key environmental factor in spaceflight, where microbes sense and respond to environmental stresses by modulating their gene expressions and altering their physiological and pathogenic processes (Wilson et al 2007; Crabbe et al 2011). Research resources in microgravity condition are extremely restricted because of the logistic reasons and safety considerations. To address this problem, high-aspect ratio rotating-wall vessels (HARVs) are extensively applied to investigate the physiological characteristics of microbes in a simulated microgravity (SMG) environment (Nickerson et al 2000; Wilson et al 2002a,b; Lynch et al 2004, 2006; Crabbe et al 2010; Lawal et al 2010; Castro et al 2011). Anaerobic culture is avoided by oxygen diffusion through a gas-permeable membrane in the back of HARVs during growth (Schwarz et al 1992; Hammond and Hammond 2001)
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