Subsurface biomolecular imaging of Streptomyces coelicolor using secondary ion mass spectrometry

Imaging using time-of-flight secondary ion mass spectrometry (TOF-SIMS) with buckministerfullerene (C(60)) primary ions offers the possibility of mapping the chemical distribution of molecular species from biological surfaces. Here we demonstrate the capability of the technique to provide biomolecular information from the cell surface as well as from within the surface, as illustrated with the distribution of two antibiotics in Streptomyces coelicolor (a mycelial bacterium). Differential production of the two pigmented antibiotics under salt-stressed and normal conditions in submerged cultivations could be detected from the TOF-SIMS spectra of the bacteria, demonstrating the potential of the technique in studying microbial physiology. Although both the antibiotics were detected on the cell surface, sputter etching with C(60)(+) revealed the spectral features of only one of the antibiotics within the cells. Exploratory analysis of the images using principal component analysis assisted in analyzing the spectral information with respect to peak contributions and their spatial distributions. The technique allows the study of not only lateral but also the depthwise distribution of biomolecules, uniquely enabling exploration of the processes within biological systems with minimal system intervention and with little a priori biochemical knowledge of relevance.