Spatially tracking (13) C-labelled substrate (bicarbonate) accumulation in microbial communities using laser ablation isotope ratio mass spectrometry.

Microbial mats are characterized by extensive metabolic interactions, rapidly changing internal geochemical gradients, and prevalent microenvironments within tightly constrained physical structures. We present laser ablation isotope ratio mass spectrometry (LA-IRMS) as a culture-independent, spatially specific technology for tracking the accumulation of (13) C-labelled substrate into heterogeneous microbial mat communities. This study demonstrates the novel LA-IRMS approach by tracking labeled bicarbonate incorporation into a cyanobacteria-dominated microbial mat system. The spatial resolution of 50 μm was sufficient for distinguishing different mat strata and the approach effectively identified regions of greatest label incorporation. Sample preparation for LA-IRMS is straightforward and the spatial selectivity of LA-IRMS minimizes the volume of mat consumed, leaving material for complimentary analyses. We present analysis of DNA extracted from a sample post-ablation and suggest pigments, lipids or other biomarkers could similarly be extracted following ablation. LA-IRMS is well positioned to spatially resolve the accumulation of any (13) C-labelled substrate provided to a mat, making this a versatile tool for studying carbon transfer and interspecies exchanges within the limited spatial confines of such systems.