Fig. 6|. The preTA operon is prevalent and functional in the gut microbiomes of colorectal cancer (CRC) patients and controls, exhibiting marked inter-individual and temporal variation in abundance.

(a) Number of samples and individuals where preTA was detected (orange) or not detected (light gray). (b) Variation in preTA abundance, as log₁₀ reads per kilobase of genome equivalents (RPKG), across CRC patients and healthy controls where preTA was detected (n=179 individuals⁵⁹). (c) Fraction of total reads mapping to preTA in CRC and control samples where it was detected (x-axis) whose best hit was in a given phylogenetic class (top) or species (bottom). Taxa are ordered by decreasing mean across all samples; samples are ordered based on hierarchical clustering using Bray-Curtis dissimilarity and complete linkage. (d) Abundance, as log₁₀ RPKG, of the preTA operon in the gut microbiome prior to and during treatment with the oral fluoropyrimidine CAP (red) or a combination of CAP and immunotherapy (blue). Lines connect measurements for the same patient. One zero RPKG value was replaced with half the minimum non-zero value prior to taking the logarithm. 3/11 patients varied over an order of magnitude during treatment (Extended Data Fig. 9). The first day of treatment is defined as day 1. Two samples collected on days −16 and 66 were censored for display purposes. (e) Bacterial isolates from a representative CRC patient stool sample in the GO Study (patient 1, Supplementary Table 12) were isolated on McConkey agar, pooled, and incubated in BHI⁺ with 5-FU for 4 days and 5-FU/DHFU were quantified by LC-QTOF/MS. p-value, two-way ANOVA contrasting 5-FU levels in sterile and inoculated media. (f) Three bacterial isolates from the same CRC patient stool sample were incubated as described in panel e (n=3 biological replicates). Lines in e,f represent means.