Effect of modeled reduced gravity conditions on bacterial morphology and physiology

Raja Vukanti,Michael A Model,Laura G Leff

doi:10.1186/1471-2180-12-4

Raja Vukanti, Michael A Model + Show 1 more

Open Access

https://doi.org/10.1186/1471-2180-12-4

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Abstract

BackgroundBacterial phenotypes result from responses to environmental conditions under which these organisms grow; reduced gravity has been demonstrated in many studies as an environmental condition that profoundly influences microorganisms. In this study, we focused on low-shear stress, modeled reduced gravity (MRG) conditions and examined, for Escherichia coli and Staphlyococcus aureus, a suite of bacterial responses (including total protein concentrations, biovolume, membrane potential and membrane integrity) in rich and dilute media and at exponential and stationary phases for growth. The parameters selected have not been studied in E. coli and S. aureus under MRG conditions and provide critical information about bacterial viability and potential for population growth.ResultsWith 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.ConclusionsOverall, 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.

Highlights

Bacterial phenotypes result from responses to environmental conditions under which these organisms grow; reduced gravity has been demonstrated in many studies as an environmental condition that profoundly influences microorganisms
S. aureus growth curves were similar under modeled reduced gravity (MRG) and normal gravity (NG) conditions, in diluted Luria Bertani (LB), OD values were consistently higher, beginning with the exponential phase of growth, under MRG than NG conditions (Figure 1C and 1D)
Higher bacterial yields were observed for both bacterial strains under MRG than NG, irrespective of the medium with the exception of E. coli grown in LB (Figure 1F)

Summary

Introduction

Bacterial phenotypes result from responses to environmental conditions under which these organisms grow; reduced gravity has been demonstrated in many studies as an environmental condition that profoundly influences microorganisms. We focused on low-shear stress, modeled reduced gravity (MRG) conditions and examined, for Escherichia coli and Staphlyococcus aureus, a suite of bacterial responses (including total protein concentrations, biovolume, membrane potential and membrane integrity) in rich and dilute media and at exponential and stationary phases for growth. Bacterial phenotypes result from responses to physical and chemical conditions under which these organisms grow [1,2,3,4]. Clinorotation provides a cost-effective, accessible approach to study these conditions relative to spacebased research and has been demonstrated to serve as an effective model for examining bacterial responses [19,21]

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