Unveiling the real-time behaviour of Staphylococcus aureus through nanomotion sensing

Iron is an essential micronutrient for bacterial growth and plays a crucial role in various physiological processes, including motility. This study investigates the influence of iron availability on the behaviour of Staphylococcus aureus, a significant human pathogen, using a nanomotion sensing technique. By correlating nanoscale vibrations with metabolically related behaviour, this sensor offers real-time insight into the activity of biological specimens from single proteins to living bacteria and mammalian cells. S. aureus cultures were grown under iron-repleted and iron-depleted conditions, and their nano-scale motility was monitored in real time. We compared the activity of wild type S. aureus with an isogenic deletion mutant, in which siderophore production was abrogated. Our results demonstrate distinct motility patterns of the two strains in response to varying iron concentrations, including different outlines of their activity. We identified the fingerprint of the iron intake pathway for the two strains: in the presence of iron, while the wild-type strain followed an exponential growth pattern, the mutant suspended its growth. Remarkably, in presence of iron, both strains showed some coordinated oscillations at well-defined frequencies, which could be related to specific behaviour of S. aureus. These results were corroborated by the phenotypic assays performed through optical microscopy and conventional growth methods. Such findings highlight the potential of nanomotion sensing, a powerful tool to study cellular vibrations and to investigate the complex relationship between iron homeostasis and S. aureus activity, suggesting this metabolic route as a possible fruitful target for the development of novel antibacterials.