Changes in Gene Expression of E. coli under Conditions of Modeled Reduced Gravity

Relatively few studies have examined bacterial responses to the reduced gravity conditions that are experienced by bacteria grown in space. In this study, whole genome expression of Escherichia coli K12 under clinorotation (which models some of the conditions found under reduced gravity) was analyzed. We hypothesized that phenotypic differences at cellular and population levels under clinorotation (hereafter referred to as modeled reduced gravity) are directly coupled to changes in gene expression. Further, we hypothesized that these responses may be due to indirect effects of these environmental conditions on nutrient accessibility for bacteria. Overall, 430 genes were identified as significantly different between modeled reduced gravity conditions and controls. Up-regulated genes included those involved in the starvation response (csiD, cspD, ygaF, gabDTP, ygiG, fliY, cysK) and redirecting metabolism under starvation (ddpX, acs, actP, gdhA); responses to multiple stresses, such as acid stress (asr, yhiW), osmotic stress (yehZYW), oxidative stress (katE, btuDE); biofilm formation (lldR, lamB, yneA, fadB, ydeY); curli biosynthesis (csgDEF), and lipid biosynthesis (yfbEFG). Our results support the previously proposed hypothesis that under conditions of modeled reduced gravity, zones of nutrient depletion develop around bacteria eliciting responses similar to entrance into stationary phase which is generally characterized by expression of starvation inducible genes and genes associated with multiple stress responses.