Surface-enhanced Raman scattering (SERS) imaging of bioactive metabolites in mixed bacterial populations

Bacteria frequently live in mixed multispecies communities, shaped by the action of bioactive metabolites that are secreted by the residing microbial species. The identification and tracking of such chemical exchange processes is fundamental toward understanding how these particular extracellular molecules modulate microbial communities and functions. In this context, most chemical imaging approaches so far have focused on the analysis of metabolic interactions occurring between microbial populations co-cultured separately. We demonstrate here the application of surface-enhanced Raman scattering (SERS) spectroscopy as a valuable imaging tool for the non-invasive detection and visualization of metabolites secreted by Escherichia coli and Pseudomonas aeruginosa bacteria, cultured as mixed populations and thereby mimicking the complexity of natural microbial communities. SERS enabled the simultaneous detection and in situ visualization of indole and pyocyanin, revealing the down-regulation of pyocyanin expression due to indole signaling. The successful detection of chemical interactions in mixed bacterial populations shows the potential of SERS for the investigation of the chemistry underpinning multispecies microbial communities. (C) 2018 Elsevier Ltd. All rights reserved.