Low-Shear Modeled Microgravity Enhances Salmonella Enterica Resis-tance to Hydrogen Peroxide Through a Mechanism Involving KatG and KatN

Francesca Pacello

doi:10.2174/1874285801206010053

Abstract

Studies carried out in recent years have established that growth under conditions of reduced gravity enhances Salmonella enterica serovar Typhimurium virulence. To analyze the possibility that this microgravity-induced increase in pathogenicity could involve alterations in the ability of Salmonella to withstand oxidative stress, we have compared the resistance to hydrogen peroxide of various Salmonella enterica strains grown under conditions of low shear modeled microgravity (LSMMG) or normal gravity (NG). We have found that growth in LSMMG significantly enhances hydrogen peroxide resistance of all the strains analyzed. This effect is abolished by deletion of the genes encoding for the catalases KatG and KatN, whose activity is markedly modulated by growth in LSMMG. In addition, we have observed that Salmonella enterica serovar Typhimurium strains lacking Hfq, RpoE, RpoS or OxyR are still more resistant to oxidative stress when grown in LSMMG than in NG conditions, indicating that these global gene regulators are not responsible for the microgravity-induced changes in KatG and KatN activity. As Salmonella likely encounters low shear conditions in the intestinal tract, our observations suggest that alterations in the relative activity of KatG and KatN could enhance Salmonella resistance to the reactive oxygen species produced also during natural infections.

Highlights

In spite of all the efforts carried out to generate and maintain microbiologically-controlled environments, several microorganisms, likely derived by contaminants and crewmember microflora, have been commonly isolated in the aircrafts employed in spaceflights [1]
To understand the effects of microgravity on Salmonella enterica, we have tested the susceptibility to hydrogen peroxide of Salmonella enterica serovar Typhimurium ATCC-14028 cultures grown in low shear modeled microgravity (LSMMG) and in normal gravity (NG) conditions
Fig. (1) shows that bacteria grown under LSMMG are significantly more resistant to hydrogen peroxide than bacteria grown under NG

Summary

Introduction

In spite of all the efforts carried out to generate and maintain microbiologically-controlled environments, several microorganisms, likely derived by contaminants and crewmember microflora, have been commonly isolated in the aircrafts employed in spaceflights [1]. A few reports have shown that microgravity conditions induce various physiological responses in bacteria, which might threaten human health during space missions These include the enhancement of virulence [2], an increase in resistance to antibiotics [3] and the induction of microbial biofilms [4]. These observations are a cause of concern as, during spaceflights, the human body experiences different kinds of stress, including changes in gravitational forces, space radiations, altered nutritional status and anxiety, which may adversely affect functionality of the immune system [5]. Typhimurium, suggesting that different microorganisms may dramatically differ in their responses to low-shear and space environments [10]

Methods

Results

Conclusion