Transcriptomic analysis of Staphylococcus xylosus in the presence of nitrate and nitrite in meat reveals its response to nitrosative stress.

Aurore Vermassen,Sabine Leroy,Rã©Gine Talon,Anne De La Foye,Valentin Loux

doi:10.3389/fmicb.2014.00691

Abstract

Staphylococcus xylosus is one of the major starter cultures used for meat fermentation because of its crucial role in the reduction of nitrate to nitrite which contributes to color and flavor development. Despite longstanding use of these additives, their impact on the physiology of S. xylosus has not yet been explored. We present the first in situ global gene expression profile of S. xylosus in meat supplemented with nitrate and nitrite at the levels used in the meat industry. More than 600 genes of S. xylosus were differentially expressed at 24 or 72 h of incubation. They represent more than 20% of the total genes and let us to suppose that addition of nitrate and nitrite to meat leads to a global change in gene expression. This profile revealed that S. xylosus is subject to nitrosative stress caused by reactive nitrogen species (RNS) generated from nitrate and nitrite. To overcome this stress, S. xylosus has developed several oxidative stress resistance mechanisms, such as modulation of the expression of several genes involved in iron homeostasis and in antioxidant defense. Most of which belong to the Fur and PerR regulons, respectively. S. xylosus has also counteracted this stress by developing DNA and protein repair. Furthermore, it has adapted its metabolic response—carbon and nitrogen metabolism, energy production and cell wall biogenesis—to the alterations produced by nitrosative stress.

Highlights

Staphylococci are commensals of the skin and mucous membranes of animals and are found in various niches (Kloos et al, 1976; Nagase et al, 2002)
In this study, determination of the global gene expression of S. xylosus in situ in meat in the presence of nitrate and nitrite at the levels used in the meat industry has allowed us to unravel the adaptive response of this bacterium to nitrosative stress
S. xylosus counteracts nitrosative stress by developing several oxidative stress resistance mechanisms such as modulation of the expression of genes involved in iron homeostasis mostly under the control of ferric uptake regulator (Fur), detoxifying enzymes mostly under the control of PerR, and DNA and protein repairs

Summary

Introduction

Staphylococci are commensals of the skin and mucous membranes of animals and are found in various niches (Kloos et al, 1976; Nagase et al, 2002). Products of animal origin are naturally contaminated by staphylococci. S. xylosus is commonly used as starter culture in meat fermentation (Talon and Leroy, 2011). This bacterium contributes to the development of flavor through its antioxidant properties and degradation of amino acids (Barrière et al, 2001a,b, 2002; Talon et al, 2002). Its main function in cured products is to reduce nitrate to nitrite which is necessary for the development of color and flavor. Besides its role in color and flavor formation, nitrite preserves meat products against growth of undesirable anaerobic bacteria and some pathogenic bacteria (Tompkin, 1995)

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Conclusion