Smell of stress: An in-depth look into the Bacillus subtilis 168 volatilome during pH stress using secondary electrospray ionization-Orbitrap mass spectrometry

Abstract

Bacillus subtilis is one of the best-studied organisms and of high importance in biotechnology. Depending on the application area, the bacterium encounters pH perturbations, potentially influencing growth and production rates. While the general stress response of B. subtilis is well studied, much is yet to be explored about its acid stress response. Using novel secondary electrospray ionization (SESI)-Orbitrap mass spectrometry technology, fermentation off-gas during acid stress applied to resting cells was measured online, in real time with a time resolution of 0.3 Hz. In total over 450 biogenic compounds were measured over 16,000 times after acidification. While some compounds were visible directly after acid addition, some increased in intensity over 2 h after the stress was induced. The most intense compounds measured in this condition were acetoin, a well-known Bacillus volatile, and C₄H₆O, which was not described before. This study provides another piece to the puzzle of the B. subtilis acid stress response by analysing the often-overlooked volatilome using a novel analytical method.