Spatially resolved analysis of glycolipids and metabolites in living Synechococcus sp. PCC 7002 using nanospray desorption electrospray ionization.

Microorganisms release a diversity of organic compounds that couple interspecies metabolism, enable communication, or provide benefits to other microbes. Increased knowledge of microbial metabolite production will contribute to understanding of the dynamic microbial world and can potentially lead to new developments in drug discovery, biofuel production, and clinical research. Nanospray desorption electrospray ionization (nano-DESI) is an ambient ionization technique that enables detailed chemical characterization of molecules from a specific location on a surface without special sample pretreatment. Due to its ambient nature, living bacterial colonies growing on agar plates can be rapidly analyzed without affecting the viability of the colony. In this study we demonstrate for the first time the utility of nano-DESI for spatial profiling of chemical gradients generated by microbial communities on agar plates. We found that despite the high salt content of the agar used in this study (~350 mM), nano-DESI analysis enables detailed characterization of metabolites produced by the Synechococcus sp. PCC 7002 colonies. High resolution mass spectrometry and MS/MS analysis of the living Synechococcus sp. PCC 7002 colonies allowed us to detect metabolites and lipids on the colony and on the surrounding agar, and confirm their identities. High sensitivity of nano-DESI enabled identification of several glycolipids that have not been previously reported by extracting the cells using conventional methods. Spatial profiling demonstrated that a majority of lipids and metabolites were localized on the colony while sucrose and glucosylglycerol, an osmoprotective compound produced by cyanobacteria, were secreted onto agar. Furthermore, we demonstrated that the chemical gradients of sucrose and glucosylglycerol on agar depend on the age of the colony. The methodology presented in this study will facilitate future studies focused on molecular-level characterization of interactions between bacterial colonies.