Abstract
Staphylococcus xylosus is used as a starter culture in fermented meat products and contributes to color formation by the reduction of nitrate to nitrite. Nitrite is a food additive that is chemically turned to nitric oxide (NO) in meat but its safety has been questioned. The objective of this study was to determine the ability of NO synthase (NOS) of S. xylosus C2a to produce NO. For this purpose, a nos deletion mutant (Δnos) in S. xylosus was constructed and NO production was evaluated in a test based on its ability to form nitrosomyoglobin and nitrosoheme. Production of NO was abrogated in the Δnos mutant under aerobic conditions and reduced about 35-40% comparing to the wild type C2a under limited oxygenation. This mutant was sensitive to oxidative stress. The expression of genes encoding catalase was modulated in the mutant with an up-regulation of katA and a down-regulation of katB and katC. The Δnos mutant displayed high colony pigmentation after prolonged growth on agar medium. Finally, the Δnos mutant showed no growth in minimal medium. Growth was not restored in the minimal medium by complementation with nos, but was restored by either addition of phenylalanine or complementation with pdt, a gene that encodes a prephenate dehydratase involved in phenylalanine biosynthesis and co-transcribed with nos. Our findings clearly demonstrate NOS-mediated NO production in S. xylosus, a meat-associated coagulase-negative Staphylococcus.
Highlights
Staphylococcus xylosus, a coagulase-negative Staphylococcus (CNS), is commonly used as starter culture to boost color development of cured meat products such as dried fermented sausages (Talon and Leroy, 2006)
Staphylococcus xylosus is commonly used as a starter culture for fermented meat products, mainly because it reduces nitrate to nitrite, which undergoes chemical reactions leading to nitric oxide (NO), which is responsible for color development (Talon and Leroy, 2006)
Our results demonstrate NO synthase (NOS)-dependent NO production in a coagulase-negative Staphylococcus
Summary
Staphylococcus xylosus, a coagulase-negative Staphylococcus (CNS), is commonly used as starter culture to boost color development of cured meat products such as dried fermented sausages (Talon and Leroy, 2006). The typical reddish color relies on the presence of the curing salts, nitrate and nitrite. Nitrate salts are reduced to nitrite by nitrate reductase activity of S. xylosus (Talon et al, 1999; Gøtterup et al, 2008). Nitrite is subsequently converted by chemical reactions to nitric oxide (NO), which is able to bind to the ferrous heme-iron to form the stable red nitrosomyoglobin pigment (Gøtterup et al, 2007, 2008). The use of the curing agents nitrate and nitrite is regulated by law, with specific indications in the United States (Code of Federal Regulations, 2016) and Europe (Commission Regulation [EU], 2011). The safety regarding the use of such additives on meat products is questioned
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