Adaptation of Staphylococcus xylosus to Nutrients and Osmotic Stress in a Salted Meat Model.

Aurore Vermassen,Emilie Dordet-Frisoni,Sabine Leroy,Pierre Micheau,Régine Talon,Anne De La Foye,Valérie Laroute

doi:10.3389/fmicb.2016.00087

Abstract

Staphylococcus xylosus is commonly used as starter culture for meat fermentation. Its technological properties are mainly characterized in vitro, but the molecular mechanisms for its adaptation to meat remain unknown. A global transcriptomic approach was used to determine these mechanisms. S. xylosus modulated the expression of about 40–50% of the total genes during its growth and survival in the meat model. The expression of many genes involved in DNA machinery and cell division, but also in cell lysis, was up-regulated. Considering that the S. xylosus population remained almost stable between 24 and 72 h of incubation, our results suggest a balance between cell division and cell lysis in the meat model. The expression of many genes encoding enzymes involved in glucose and lactate catabolism was up-regulated and revealed that glucose and lactate were used simultaneously. S. xylosus seemed to adapt to anaerobic conditions as revealed by the overexpression of two regulatory systems and several genes encoding cofactors required for respiration. In parallel, genes encoding transport of peptides and peptidases that could furnish amino acids were up-regulated and thus concomitantly a lot of genes involved in amino acid synthesis were down-regulated. Several genes involved in glutamate homeostasis were up-regulated. Finally, S. xylosus responded to the osmotic stress generated by salt added to the meat model by overexpressing genes involved in transport and synthesis of osmoprotectants, and Na+ and H+ extrusion.

Highlights

Meat fermentation is an old process that relies on indigenous microbiota and is nowadays carried out under controlled conditions with addition of starter cultures
S. xylosus was collected at the early stationary phase of growth in a minimal medium and was inoculated in the meat model at 7.7 log CFU/g
The in situ S. xylosus response revealed a global change in gene expression during its survival in the meat model by comparison with the inoculum

Summary

Introduction

Meat fermentation is an old process that relies on indigenous microbiota and is nowadays carried out under controlled conditions with addition of starter cultures. Meat starter cultures are composed of a combination of lactic acid bacteria and coagulase-negative staphylococci (Ravyts et al, 2012). Staphylococcus xylosus and Staphylococcus carnosus are the two main staphylococcal species used as starter cultures. They are associated with different species of Lactobacillus, such as Lactobacillus sakei or Lactobacillus curvatus or Pediococcus. Studies over decades of microorganisms used as starters have yielded information about their potential functionalities in meat products. Lactic acid bacteria are well-known acidifiers and bacteriocin producers that affect the technological properties and the microbial stability of products (Leroy et al, 2006). Staphylococci are recognized to play an important role in the color formation through their nitrate

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Conclusion