Capturing bacterial metabolic exchange using thin film desorption electrospray ionization-imaging mass spectrometry

Abstract

Over 60% of current pharmaceutical drugs have origins in natural products. To expand on current methods allowing one to characterize natural products directly from bacterial culture, herein we describe the use of desorption electrospray ionization (DESI) imaging mass spectrometry in monitoring the exchange of secondary metabolites between Bacillus subtilis and Streptomyces coelicolor using a simple imprinting technique.

Figure 1

Monitoring secondary metabolite production by DESI imaging mass spectrometry (IMS). A) IMS of Millipore HA filter imprints of Bacillus subtilis 3601 wild type (WT) and PY79 mutant strain cultured with Streptomyces coelicolor A3(2). Signals corresponding to surfactin (m/z 1035) and plipastatin (m/z 1504) can be seen localized to the B. subtilis 3610 wild type colony while signals corresponding to the purple pigmented antibiotic actinorhodin (m/z 629) and an unknown ion (m/z 1076) can be seen localized to the S. coelicolor colony. B) Distribution of unique ion signals between B. subtilis 3610 wild type and PY79 mutant strains and between S. coelicolor colonies cultured with B. subtilis 3610 and PY79. For surfactin and plipastatin, only ions corresponding to the [M-H]⁻ ions were included with other charge states excluded from the count. C) Identification of the signal at m/z 629 as actinorhodin by comparing tandem MS fragmentation patterns for HPLC purified actinorhodin extracts (top) and data from the HA filter imprint of the bacterial colony (bottom). D–E) Tandem MS confirmation of surfactin (D) and plipastatin (E) from B. subtilis 3610 wild type directly from HA filter imprint of the bacterial colony.