Differentiation of microbial species and strains in coculture biofilms by multivariate analysis of laser desorption postionization mass spectra

Abstract

7.87 to 10.5 eV vacuum ultraviolet (VUV) photon energies were used in laser desorption postionization mass spectrometry (LDPI-MS) to analyze biofilms comprised of binary cultures of interacting microorganisms. The effect of photon energy was examined using both tunable synchrotron and laser sources of VUV radiation. Principal components analysis (PCA) was applied to the MS data to differentiate species in Escherichia coli-Saccharomyces cerevisiae coculture biofilms. PCA of LDPI-MS also differentiated individual E. coli strains in a biofilm comprised of two interacting gene deletion strains, even though these strains differed from the wild type K-12 strain by no more than four gene deletions each out of approximately 2000 genes. PCA treatment of 7.87 eV LDPI-MS data separated the E. coli strains into three distinct groups, two “pure” groups, and a mixed region. Furthermore, the “pure” regions of the E. coli cocultures showed greater variance by PCA at 7.87 eV photon energies compared to 10.5 eV radiation. This is consistent with the expectation that the 7.87 eV photoionization selects a subset of low ionization energy analytes while 10.5 eV is more inclusive, detecting a wider range of analytes. These two VUV photon energies therefore give different spreads via PCA and their respective use in LDPI-MS constitute an additional experimental parameter to differentiate strains and species.

Ion sources for mass spectrometric identification and imaging of molecular species

“…92,94 For example, ns-LDPI-MS was used to probe a single bacterial biolm consisting of two genetically engineered strains of Escherichia coli grown on the same substrate under identical conditions, then analyzed in intact form. 95 10.5 eV photons ionized the (ns, UV) laser desorbed neutrals to obtain the mass spectrum shown in Fig. 5(a).…”

“…Photon energy tunable VUV radiation available at synchrotron light sources has also been used for ns-LDPI analysis. 19,21,91,92,[95][96][97] Tunable VUV provides the distinct advantage of selectively ionizing different classes of compounds; a recent study of organic-mineral soil samples showed that tuning the VUV photon energy and the UV laser parameters allowed control of fragmentation of the organic analyte and enabled compounds identication with less ambiguity. 98 Overall, ns-LDPI does not display the interfering intense matrix peaks that appear in MALDI, permitting more useful information to be obtained from the low mass region (m/z < 300) of the spectra.…”

An Experimental and Theoretical Study of Laser Postionization of Femtosecond-Laser-Desorbed Drug Molecules

“…In addition, 7.9 eV single-photon ionization has been coupled to nanosecond laser desorption, − enabling even molecules larger than 10 000 Da to be detected . Laser-based single-photon ionization has more recently been combined with femtosecond laser desorption (fs-LD) at the University of Illinois at Chicago (UIC) for MS imaging of molecular species in biofilms , with near-micrometer lateral resolution (as measured on test samples) .…”

Symbiosis-inspired approaches to antibiotic discovery

“…199–203 Untargeted metabolomic analysis of combined versus axenic cultures enables the study of large numbers of microbial combinations. In contrast to the labor intensive and less informative comparative approaches which required manual comparison of chromatographic (often UV or TLC) data, recent metabolomics approaches including principal component analysis (PCA) and partial least-squares regression (PLS-DA) identifies molecular features on the basis of mass-to-charge ( m/ z) and retention time.…”