One of the biggest challenges in microbiome research in environmental and medical samples is to better understand functional properties of microbial community members at a single cell level. Single cell isotope probing has become a key tool for this purpose, but the currently applied detection methods for measuring isotope incorporation into single cells do not allow high-throughput analyses. Here, we report on the development of an imaging-based approach termed stimulated Raman scattering - two-photon fluorescence in situ hybridization (SRS-FISH) for high-throughput function-identity analyses of microbial communities with single cell resolution. SRS-FISH has an imaging speed of 10 to 100 milliseconds per cell, which is two to three orders of magnitude faster than spontaneous Raman-FISH. Using this technique, we delineated metabolic responses of thirty thousand individual cells to various mucosal sugars in the human gut microbiome via incorporation of deuterium from heavy water as an activity marker. Application of SRS-FISH to investigate the utilization of host-derived nutrients by two major human gut microbiome taxa revealed that response to mucosal sugars tends to be dominated by Bacteroidales, with an unexpected finding that Clostridia can outperform Bacteroidales at foraging fucose.
Tunable Expression Tools Enable Single-Cell Strain Distinction in the Gut Microbiome