Tougher and more virulent?
Human biology presents numerous limitations when it comes to space travel. Bacteria are more adaptable, robust and resilient, and are known to thrive in even the most extreme environments. But how do they fare in space? To date, numerous bacterial experiments have been conducted in Earth’s orbit. We know that bacteria grown in space exhibit a number of differences relative to their behavior on Earth.
What are the observed differences? A reduced lag phase and increased final population density have been consistently reported for non-motile, suspension cultures (1). Improved biofilm formation (2-3), higher specific productivity of secondary metabolites (4), a thicker cellular envelope (5) and enhanced conjugation efficiency (6) have also all been documented. Aside from these altered growth characteristics, there have also been reports of increased virulence (7–8) and a reduced susceptibility to antibiotics (9–15). Radiation worries aside, these findings are clearly alarming for crew on manned missions, for example on the International Space Station, as these health-related findings present new challenges when it comes to treatment of potential infections. The key question is what are the underlying molecular mechanisms responsible for the “strange” behavior exhibited by bacterial cells in space?
Microgravity is to blame. Changes in bacterial behavior are thought to be due to reduced mass transport in the local extracellular environment. In the absence of gravity-dependent convection, movement of molecules consumed and excreted by the cell is limited to diffusion. In order to test this hypothesis, a new study by Zea et al. evaluated differential gene expression in E. coli suspension cultures grown in space and on Earth (16). The team extracted RNA using QIAGEN’s RNeasy Mini Kit for use in RNA-seq library preparation, and performed data analysis with QIAGEN’s CLC Genomics Workbench. They aimed to demonstrate an overexpression of genes linked to a reduction in extracellular mass transport. These included genes associated with starvation and the utilization of alternative energy sources, increases in metabolism, enhancement of acetate production and other systematic responses to acidity. The team’s gene expression data confirmed that reduced extracellular mass transport is the primary underlying gravity-dependent, physical mechanism responsible, at least in part, for the altered behavior that bacteria typically exhibit in space (16).
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