Using NMR Metabolomics to Investigate Tricarboxylic Acid Cycle-dependent Signal Transduction in Staphylococcus epidermidis

Steven Halouska,Greg A. Somerville,Yefei Zhu,Bo Zhang,Marat R. Sadykov,Jennifer L. Nelson,Lauren W. Kreimer,Robert Powers

doi:10.1074/jbc.m110.152843

Steven Halouska, Greg A. Somerville + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m110.152843

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Abstract

Staphylococcus epidermidis is a skin-resident bacterium and a major cause of biomaterial-associated infections. The transition from residing on the skin to residing on an implanted biomaterial is accompanied by regulatory changes that facilitate bacterial survival in the new environment. These regulatory changes are dependent upon the ability of bacteria to "sense" environmental changes. In S. epidermidis, disparate environmental signals can affect synthesis of the biofilm matrix polysaccharide intercellular adhesin (PIA). Previously, we demonstrated that PIA biosynthesis is regulated by tricarboxylic acid (TCA) cycle activity. The observations that very different environmental signals result in a common phenotype (i.e. increased PIA synthesis) and that TCA cycle activity regulates PIA biosynthesis led us to hypothesize that S. epidermidis is "sensing" disparate environmental signals through the modulation of TCA cycle activity. In this study, we used NMR metabolomics to demonstrate that divergent environmental signals are transduced into common metabolomic changes that are "sensed" by metabolite-responsive regulators, such as CcpA, to affect PIA biosynthesis. These data clarify one mechanism by which very different environmental signals cause common phenotypic changes. In addition, due to the frequency of the TCA cycle in diverse genera of bacteria and the intrinsic properties of TCA cycle enzymes, it is likely the TCA cycle acts as a signal transduction pathway in many bacteria.

Highlights

Being skin-resident to residing on implanted biomaterials necessitates the need for changes in the expression of genes coding for enzymes required for growth in the new environment
Ethanol-stressed bacteria are in the post-exponential growth phase at 6 h after inoculation, their growth is slower, which slows the consumption of glucose, and excess glucose can repress transcription of tricarboxylic acid (TCA) cycle genes
To determine the metabolic changes associated with iron limitation, ethanol stress, and TCA cycle inactivation, NMR metabolomic analysis [28, 29] was used to assess the stressed and non-stressed metabolomes of strains 1457 and the TCA cycle inactive strain 1457-acnA

Summary

Introduction

Being skin-resident to residing on implanted biomaterials necessitates the need for changes in the expression of genes coding for enzymes required for growth in the new environment. The activity of TCA cycle enzymes is affected by the availability of nutrients and a variety of stressinducing stimuli (9 –12); the availability of biosynthetic intermediates, the redox status, and the energy status can be altered by nutritional and environmental stimuli These observations led us to propose a fourth function for the TCA cycle, the transduction of external signals into intracellular metabolic signals that can be “sensed” by metabolite-responsive regulatory proteins [2]. With the exception of the succinate dehydrogenase complex, most TCA cycle enzymes are not membrane-associated; it is reasonable to predict that the deleterious effects of ethanol stress are largely independent of the TCA cycle Taken together, these observations suggest that disparate environmental conditions will cause divergent metabolomic changes. To test our central hypothesis, we chose to induce environmental stress by growing bacteria in an iron-limited medium or in a medium containing ethanol and assessing the metabolic changes using NMR metabolomics

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