Analysis of single‐cell microbial mass spectra profiles from single‐particle aerosol mass spectrometry

Abstract

Rationale Single‐particle aerosol mass spectrometry is a practical method for studying microbial aerosols. However, the related mass spectral characteristics of single‐cell microorganisms have not yet been studied systematically; hence, further investigations are necessary. Methods Different microbial cells were grown and directly aerosolized in the laboratory. These aerosols were then drawn into a single‐particle mass spectrometer platform, and single‐cell mass spectra profiles were obtained in real‐time. The biological characteristics, ion variation trends, and microbial types were analyzed with either laser pulse energy or laser fluence. Results The single‐particle mass spectra contained prominent peaks that could be attributed to the presence of biological matter, such as organic phosphate and nitrogen, amino acids, and spore‐associated calcium complexes. Limited types of average mass spectral patterns were present, and a significant correlation was found between the ion intensity trend (presence and absence of peaks) and laser ionization energy (expressed by the total positive ion intensity). Although a single spectral data point does not contain all the peaks of the average spectrum, it covers most of the characteristic peaks and could be identified using a machine learning algorithm. After the analysis of single‐particle mass spectra, we found that using multi‐group features (e.g., peak intensity ratio of m/z +47 and +41, peak intensity ratio of 59N(CH3)3+ and 74N(CH3)4+, and 12 peak variables) led to an identification accuracy of approximately 92.4% with the random forest algorithm. Conclusions The results indicate that single‐cell mass spectral profiles can be used to distinguish microbial aerosols and further illustrate their origin in a laboratory setting.

Infrared Multiphoton Dissociation Enables Top‐Down Characterization of Membrane Protein Complexes and G Protein‐Coupled Receptors

“…We utilize MD simulations to rationalize this and found that some of the transmembrane regions which maintain their helicity at high temperatures are prone to fragmentation, giving credence to our hypothesis that protons can both stabilize and induce successive peptide bond cleavage through migration along the protein backbone, resulting in the fragmentation patterns observed above. The ability to extract structural information from native top‐down MS of soluble and membrane proteins has been demonstrated using various activation modalities, so it is conceivable that an enduring influence of the protein ion structure is reflected in the distribution of product ions [14d,17,18e–f,41] …”

Bioaerosol Identification by Wide Particle Size Range Single Particle Mass Spectrometry

“…SPMS single-step laser desorption is a difficult ionization process in which organic compounds produce ion fragments of different degrees. Liu et al [37] used Bacillus thuringiensis to explore the influence of different laser pulse energies on SPAMS and found that particles do not ionize when the laser energy is lower than 0.2 mJ•pulse −1 and that the ionic peak increases significantly when the laser energy is higher than 1.5 mJ•pulse −1 ; they also found that particle integrity is the best when the laser energy is about 0.5 mJ•pulse −1 . Too-high or too-low energy is not conducive to the discovery of the characteristic mass spectrum.…”

Technical Note: Bioaerosol identification by wide particle size range single particle mass spectrometry

“…Through this method, environmental particles with both dust and characteristic biological spectra fingerprints were successfully excluded from the classification of biological particles. Liu et al (2021) used Bacillus thuringiensis to explore the influence of different laser pulse energies on SPAMS and found that particles did not ionize when the laser energy was lower than 0.2 mJ and that the ionic peak increased significantly when the laser energy was higher than 1.5 mJ; they also found that the ionic peak integrity was the best when the laser energy was about 0.5 mJ. Too high or too low energy was not conducive to the discovery of the characteristic mass spectrum.…”