Differentiation of the metabolic profile of actinobacteria isolated from the soil of the caatinga biome by paper spray mass spectrometry

Paper spray mass spectrometry (PS-MS) is an ambient ionization technique that allows for rapid and direct mass spectrometry analysis for a wide range of chemical compounds due to its portability, little to no sample preparation, and cost-effective materials. As applications with this technique continue to expand, the identification and discrimination of bacteria at the strain level remain a promising avenue for researchers. Although studies in the past demonstrated the applicability of PS-MS to discriminate bacteria at the strain level, no one has reported the strain-level differentiation of actinobacteria without using solvent for PS-MS. Hence, this study demonstrates that optimization of PS-MS permits the investigation and differentiation of the metabolic profiles of actinobacteria without the need for solvents, diminishing the potential for sample contamination and consequently increasing the versatility of this technique. In doing so, strains of actinobacteria (CAAT P5–21, CAAT P5–16, CAAT 8–25, CAAT P8–92, and CAAT P11–13) were grown and transferred to produce a crude growth medium. The supernatant was used for the PS-MS analyses using a Thermo Scientific LTQ mass spectrometer. Multivariate statistical analysis, including principal component analysis (PCA) and hierarchal cluster analysis (HCA), was employed to chemically distinguish the strains of bacteria. As a result, each strain of actinobacteria could be visually differentiated based on their metabolic profile. These findings demonstrate the practicability of using a liquid medium as an alternative to many other organic solvents when analyzing bacteria, making PS-MS a crucial addition to a microbiologist's research toolkit.