Selection and transcriptomic analysis of coagulase-negative Staphylococcus with high proteolytic activity isolated from Chinese Dong fermented pork (Nanx Wudl)

Although coagulase-negative Staphylococcus (CNS), along with technological activities, plays a key role in fermented sausage flavour and nutrient production, the molecular mechanism of these activities remains elusive. In this study, 18 CNS strains with high proteolytic activity were isolated from Chinese Dong fermented pork (Nanx Wudl), and their technological and transcriptomic properties were investigated. After biochemical identification and genetic analysis, their technological properties, including nitrate reductase, catalase, antioxidant, and lipolytic activities and their growth under varying temperatures, salt concentrations, and pH levels were evaluated. Their aroma-producing potential was also determined in a model medium resembling fermented sausages. Transcriptomic analysis was performed using the most promising isolates. Biochemical identification and 16S rDNA sequencing revealed that the 18 Staphylococcus strains belonged to Staphylococcus xylosus, Staphylococcus saprophyticus, Staphylococcus carnosus, Staphylococcus sciuri, and Staphylococcus equorum. In terms of technological properties, 16 strains showed a nitrate-reducing ability, while 11 strains had a lipolytic activity. All strains exhibited superoxide dismutase (SOD) and catalase activities; four strains displayed an SOD activity of > 50%. They also tolerated 10% NaCl and 150 mg/kg of nitrite. They showed significant differences in ketone and acid production. The transcriptomic analysis of S. xylosus strains Sx3 and Sx6, which were selected because of their excellent enzymatic activities and aroma-producing ability, revealed the remarkable effect of genes related to pyruvate catabolism and amino acid metabolism on aroma generation. Therefore, this study provided valuable insights into the metabolic mechanisms underlying the technological properties of CNS and identified promising candidates as starter cultures in fermented sausage manufacturing.