USING IMAGING MASS SPECTROMETRY TO STUDY BACTERIAL SOCIALITY: THE ROLE OF SECONDARY METABOLITES IN SPATIAL COMMUNITY STRUCTURES

Rachel Gregor ^1,2 Yonghui Dong ³ Sofya Sudin ^1,2 Asaph Aharoni ³ Itzhak Mizrahi ^2,4 Pieter C. Dorrestein ^5,6 Michael M. Meijler ^1,2

¹Department of Chemistry, Ben-Gurion University of the Negev, Beersheva, Israel
²National Institute of Biotechnology in the Negev, Ben-Gurion University of the Negev, Beersheva, Israel
³Department of Plant and Environmental Sciences, Weizmann Institute of Science, Beersheva, Israel
⁴Department of Life Sciences, Ben-Gurion University of the Negev, Beersheva, Israel
⁵Collaborative Mass Spectrometry Innovation Center, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, USA
⁶Center for Microbiome Innovation, University of California San Diego, La Jolla, USA

Quorum sensing (QS) describes the ability of a population of bacteria to synchronize communal gene expression through the secretion and recognition of small diffusible molecular signals. QS is dependent on increases in cell density and the resulting local increase in concentration of signaling molecules, and therefore is relevant to understanding bacterial sociality and the emergence of spatial structure in mixed bacterial communities. Such structure has variously been linked to genetic drift, growth rates, nutrient limitation, and other phenomena.

We are interested in the role of secondary metabolites, especially siderophores, signaling molecules, and other QS-regulated “common goods,” in governing the organization and interactions within a community. Using Pseudomonas aeruginosa as a model system, we study the development of spatial structure and metabolite distribution in mixed communities of wild-type bacteria together with strains that are impaired in the production of various common goods due to knockouts of relevant QS signaling pathways.

To this end, we utilize matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). This technique provides a macro-scale view of bacterial information flow by directly imaging metabolite secretion from colonies grown on agar, resulting in heat maps of metabolite distribution over a wide range of masses. We use MALDI-IMS to track the production and diffusion of relevant secondary metabolites between the wild-type and mutant strains, and to address how such metabolite flow can shape the spatial structure of a mixed community.