Analysis of Escherichia coli Flagellin Gene Expression in Simulated Spaceflight Growth Conditions
Population growth curves of Escherichia coli (E. coli) cultures propagated in spaceflight environments demonstrate an extended log phase duration and an increased final cell concentration compared to E. coli cultures grown on Earth. We suggest that during spaceflight, a lack of convective mixing in the growth medium alters a cells microenvironment such that the cell at first devotes its resources primarily to motility and later shifts most of its resources to reproduction. As flagellin is the major protein component of flagella, the motility structure of E. coli, we propose that the expression of the flagellin gene (fliC) can be used as a diagnostic marker for determining if the bacterium is in fact altering its allocation of cellular resources to motility during specific growth phases. We have used semiquantitative RT-PCR to analyze the expression of fliC in cultures grown in laboratory apparatus that simulate various aspects of the spaceflight environment. The data from this pilot study indicate that fliC expression increases initially under stationary, slow clinorotation, and fast clinorotation growth conditions, peaking at mid-exponential phase and decreasing dramatically in stationary phase. These data support the hypothesis that metabolic resources are being directed towards forming the flagellum, the bacteria motile structure, before shifting resources to growth, reproduction, and maintenance.