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Effect of modeled reduced gravity conditions on bacterial morphology and physiology

DOI: 10.1186/1471-2180-12-4

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Abstract:

With the exception of S. aureus in dilute Luria Bertani (LB) broth, specific growth rates (based on optical density) of the bacteria were not significantly different between normal gravity (NG) and MRG conditions. However, significantly higher bacterial yields were observed for both bacteria under MRG than NG, irrespective of the medium with the exception of E. coli grown in LB. Also, enumeration of cells after staining with 4',6-diamidino-2-phenylindole showed that significantly higher numbers were achieved under MRG conditions during stationary phase for E. coli and S. aureus grown in M9 and dilute LB, respectively. In addition, with the exception of smaller S. aureus volume under MRG conditions at exponential phase in dilute LB, biovolume and protein concentrations per cell did not significantly differ between MRG and NG treatments. Both E. coli and S. aureus had higher average membrane potential and integrity under MRG than NG conditions; however, these responses varied with growth medium and growth phase.Overall, our data provides novel information about E. coli and S. aureus membrane potential and integrity and suggest that bacteria are physiologically more active and a larger percentage are viable under MRG as compared to NG conditions. In addition, these results demonstrate that bacterial physiological responses to MRG conditions vary with growth medium and growth phase demonstrating that nutrient resources are a modulator of response.Bacterial phenotypes result from responses to physical and chemical conditions under which these organisms grow [1-4]. Variation in environmental conditions, for example, changes in temperature [5-7] and availability of nutrients [8-10], alter bacterial responses. Reduced gravity is one such environmental factor that profoundly influences microorganisms [e.g., [11-15]]. Specifically, in this study, we focus on low-shear stress, reduced gravity conditions (< 0.001 Pa; [16]) as a model. This model reflects conditions in which imp

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