Vitamin K2 production by Staphylococcus shinii IMDO-S216 is affected by high oxygen exposure
Microbial production of vitamin K2 (MK-n), and MK-7 in particular, is of interest because of its health-associated benefits. While oxygen favours vitamin K2 yields in lactic acid bacteria and in the genus Bacillus, less is known about its effects on food-grade staphylococci. Staphylococcus shinii IMDO-S216, a strain belonging to a recently described species genetically similar to Staphylococcus xylosus and isolated from fermented meat, was grown under high oxygen supply in brain heart infusion at pH 7.0 and 30°C for 48 h. Its MK-7 production dynamics were followed alongside transcriptomic analysis of genes related to vitamin K2 biosynthesis, energy metabolism, and antioxidant defences. Over time, the MK-7 concentrations within S. shinii IMDO-S216 biomass decreased from 688 nmol to 7 nmol per gram of cell dry mass, while concentrations in the supernatant remained stable at 8 nmol/L. This decrease was probably linked to oxidative degradation, paralleling an increased expression of ROS-detoxifying genes (sodA, katB, katC, bsaA, and ohrA). Furthermore, the qorA gene, which is linked to semiquinone radical and superoxide anion formation from quinones, seemed to be involved in the initial stages of menaquinones degradation. Moreover, the increasing relative abundance of MK-6 compared to MK-7 over time may reflect an adaptive survival strategy of S. shinii IMDO-S216, involving extracellular electron transfer . In conclusion, high oxygen levels turned out to exert an unfavorable influence on MK-n production by S. shinii IMDO-S216.