Gut phageome meta-analysis of 23 FMT studies
We analyzed 23 FMT studies, spanning North America (11 from the USA and one from Canada), Europe (3 from Netherlands, 2 from Italy, one from France and one from the European part of Russia), Asia (2 from Israel and one from mainland China) and Oceania (one from New Zealand) including 1,970 fecal metagenomes from healthy donors and FMT recipients across 10 conditions (patients with 9 diseases and healthy volunteers) (Fig. 1a). Metagenomes were assessed for quality and assembled to identify viral contigs (Fig. 1b). We detected a total of 103,402 viral operational taxonomic units (vOTUs) which were further filtered according to the Uncultivated Virus Genome (MIUViG) standards to obtain 29,208 vOTUs with medium-to-high quality and completeness (Fig. 1c). Only 1,690 of filtered vOTUs were classified into at least one viral cluster (VC) with known reference genomes of uncultured viruses (Fig. 1d). Among these classified vOTUs, >95% of vOTUs belonged to families Kyanoviridae (former Myoviridae, 51.95%), Drexlerviridae (former Siphoviridae, 31.54%) or Autographiviridae (former Podoviridae, 11.72%). (Fig. 1e, Supplementary Table 4). 13,905 (47.61 %) of vOTUs we predicted to have temperate lifestyle and 15,273 (52.29 %) vOTUs were predicted to have lytic lifestyle (Fig. 1f, Supplementary Table 5). Most of classified vOTUs were predicted to bacterial hosts Gammaproteobacteria, Clostridia, Bacilli and Bacterodia at the class level (Fig. 1g, Supplementary Table 6).
FMT lead to increased phageome diversity and shift towards donors
We first compared phageome diversity, measured by the Shannon index, between different recipient conditions and donor groups. FMT recipients with rCDI consistently showed lower phageome diversity at baseline compared to donors, and shifted to higher phageome diversity after FMT (Fig. 2a). Although we observed similar trends in FMT recipients with MDRB infections and IBD, we did not observe statistically significant differences between recipients and donors, or shifts between pre- and post-FMT diversities in other cohorts (Supplementary Table 7). Gut phageome of pre-FMT recipients under different conditions was significantly differentiated from donors and recipients after FMT (Fig. 2b, PERMANOVA based on Bray-Curtis dissimilarities, P < 0.001, R2 = 3%). Especially, samples from rCDI patients clustered separately from other FMT recipients (Fig. 2c). We observed significant differences in beta-diversities within donors (PERMANOVA, P < 0.001, R2 = 36%) and pre-FMT recipients (PERMANOVA, P < 0.001, R2 = 28%) between different cohorts (Supplementary Fig. 1a, b), highlighting potential geographical, technical and other confounding effects present in these data. Phage profiles significantly shifted towards those of their donors in approximately 75.81% and 69.09% of recipients with rCDI and MDRB infections, respectively (Fig. 2d). After evaluating confounders (Supplementary Fig. 2) and excluding those vOTUs that were significantly correlated with the sequencing depth, country or study cohort, approximately 23.41% (6,837 of 29,208) of vOTUs showed a statistically significant difference between donors and recipients (pre- or post-FMT). Among these, 93.92% (6,421 of 6,837) of differentially abundant vOTUs displayed greater relative abundance in both donors and post-FMT recipients compared to recipients at baseline (Fig. 2e, Supplementary Table 8). For those with taxonomic classification, 24.55% (205 of 835) of temperate phages and 24.24% (207 of 854) of lytic ones showed significant difference between donors and recipients (pre- or post-FMT) (Fig. 2e). This indicates major phageome shifts post-FMT and a wide scale donor phage engraftment in FMT recipients.
Phageome engraftment outcomes varied across patient conditions
We next compared post-FMT samples to samples with their matched donors to determine different engraftment and persistence outcomes of phages in recipients (Fig. 3a). We identified six outcomes for each phage in post-FMT recipient metagenomes: colonization (donor phages observed in the recipients post-FMT); novel phages (either phages not observed in donors and pre-FMT recipients were introduced, or the low-abundance phages that had colonized were expanded); coexistence of phages shared by donor and recipient; persistence (recipient phages that were not detectable in donors and persisted through FMT); rejection (absence of detectable engraftment of donor phages); and loss of recipient phages after FMT (Fig. 3b, Supplementary Table 3). The resilience of recipient phages accounted for only 3.51 ± 2.19% to 10.46 ± 2.85%, while 37.32 ± 21.04% to 75.69 ± 6.48 % of phage outcomes could not be determined (Fig. 3c). More phages from donors or those from either environmental or previously undetected took over phage communities of recipients with rCDI after FMT, while novel donor and environmental phages accounted for, on average, 16.11 ± 8.2% to 39.37 ± 18.91% of the total post-FMT phageome in other recipient groups (Fig. 3c). Phage engraftment outcomes varied considerably in different conditions (Fig. 3d). There was a higher rate of engraftment in FMT cases of rCDI (colonization and novel phages, accounting for 25.79 ± 12.26% and 33.37 ± 13.59% post-FMT phages, respectively). In contrast, coexistence (24.57 ± 14.15%) was the most common outcome cases where phages were present in both donors and pre-FMT recipients, mainly in FMT cases of healthy volunteers and noninfectious diseases (except rCDI and MDRB infections, 31.89 ± 10.08%) (Fig. 3d). We observed phage from all six engraftment outcome groups in each donor-recipient pair and none of the recipients showed complete phage turnover or complete rejection after FMT, despite persistent recipient phages or engrafted phages being rare (Fig. 3d). These results show that phage engraftment varies in different diseases. Recipients with infectious diseases, such as rCDI or MDRB infections, may experience more phage engraftment after FMT.
More abundant temperate phages were associated with engraftment outcomes
To determine whether phage lifestyles were associated with engraftment outcomes, we compared the phage lifestyles before and after FMT across diseases. Overall, temperate phages were more abundant compared to lytic phages in both donors and recipients (Fig 4a). Phages belonging to different engraftment outcome groups showed relatively even proportions of temperate and lytic phage with few exceptions (Fig4. b-e, Supplementary Fig. 3a). Post-FMT healthy volunteers exhibited a higher proportion of lytic phages within novel phages with an unknown source (Fig. 4b) and post-FMT samples from rCDI patients were colonized with slightly more temperate than lytic donor phages (Fig. 4c, Supplementary Fig. 3a). Notably, temperate phages (59.63 ± 5.99%) showed a predominance in phages where the colonization outcome was undetermined (i.e. the vOTU was detected in the donor and pre- and post-FMT recipient samples) (Fig. 4d, Supplementary Fig. 3a). Among vOTUs persistent in FMT recipients (detected both pre- and post-FMT), temperate phages were more common among patients with rCDI (Fig. 4e, Supplementary Fig. 3a). In contrast, we observed more persistent lytic phages in healthy volunteers and recipients with melanoma or metabolic syndrome (Fig. 4d). No statistically significant pairwise differences between donor and recipient samples emerged within either lifestyle before or after FMT when all FMT studies were combined (Fig. 4a). However, relative abundances of temperate phages in approximately 85.38% of donors (292 from 14 datasets) were significantly higher than phages with lytic lifestyle (Supplementary Fig. 3b, Supplementary Table 9). Particularly, 80.2% of recipients with rCDI (243 from 8 datasets) showed higher relative abundances of temperate phages post-FMT compared to pre-FMT (51.77%, 141 from 3 datasets) (Supplementary Fig. 3b, Supplementary Table 9). As an exception, healthy volunteers with equal relative abundances of temperate and lytic phages pre-FMT presented a trend towards donors with relatively higher abundance of lytic phages post-FMT, albeit the difference was not no statistically significant (Supplementary Fig. 3b, Supplementary Table 9). The phageome shift within phage lifestyles varied between patient conditions and FMT studies (Fig. 4f, Supplementary Fig. 3c). Both temperate and lytic recipient phage profiles shifted towards those of their donors in approximately 56% of recipients (Supplementary Fig. 3c). On average, both temperate and lytic phage profiles of recipients with infectious diseases (rCDI and MDRB infections) significantly shifted towards those of their donors after FMT (95% CI of temperate phages: 0.029-0.048 and 0.005-0.03, respectively; lytic phages: 0.034-0.059 and 0.009-0.04, respectively) (Fig. 4f). Taken together, FMT might favor colonization of temperate phages, especially in patients with rCDI, potentially through stable engraftment of their bacterial hosts.
Phage AMGs carriage and diversity differed by lifestyle
The auxiliary metabolic genes (AMGs) have been found in many phages, which can be traced back to bacterial hosts and assist in regulating host metabolism [42]. We annotated a total of 11,505 AMGs across 26.53% (7,750 of 29,208) of the vOTUs (Fig. 5a). Approximately 22.82% (2,625 of 11,505) and 8.59% (988 of 11,505) of AMGs were assigned to the DNA (cytosine-5)-methyltransferase (dcm) and S-adenosylmethionine synthetase (metK), respectively (Fig. 5b). Both of them are involved in the cysteine and methionine metabolism. At the KO level, AMGs were enriched in 22 pathways (Fig. 5c, P < 0.05). Among these, the glycolysis / gluconeogenesis pathway was statistically most significant (Fig. 5c), implying its potential role in providing upstream compounds of amino acids biosynthesis. We further asked whether temperate and lytic phages differed in terms of AMG carriage and whether this had potential implications in metabolism of post-FMT microbiomes. AMG compositions differed significantly between temperate and lytic phages (Fig. 5d, PERMANOVA, P < 0.001, R2 = 3%). In addition, both Shannon and richness indexes of AMG profiles were significantly higher in temperate than lytic phages (Fig. 5e, f), implying that temperate phages harbor more AMGs compared to lytic phages. Most pathways, especially the cysteine and methionine metabolism, harbored higher proportion of AMGs from temperate phages compared to lytic phages (Fig. 5g). More abundant and highly diverse AMGs in temperate phages might contribute more to regulate bacterial metabolism, especially the glycolysis / gluconeogenesis pathway and the metabolism of cysteine and methionine.
AMGs in phageome may support and regulate gut microbial metabolism after FMT
We found that cysteine and methionine metabolism genes were enriched among AMGs with potential implications throughout the human lifespan. For example, early-life fecal cysteine levels are positively associated with neurological and physical development [47]. On the other hand, AMGs that assist bacterial methionine metabolism in centenarians may be related to their longevity [48]. In order to investigate these pathways in detail, we combed 33 AMGs related to cysteine and methionine metabolism with potential to regulate microbial metabolism and their abundance in donors and changes in recipients after FMT (Fig.6). In glycolysis, AMGs encoding glucose-6-phosphate isomerase (pgi), fructose-bisphosphate aldolase (class II, fbaA), glyceraldehyde 3-phosphate dehydrogenase (gapA), phosphoglycerate kinase (pgk), 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase (gpmA), pyruvate kinase (pyk) and lactate dehydrogenase (ldh) were significantly increased after FMT potentially promoting the metabolism of α-D-Glucose 6-phosphate to lactate (Supplementary Fig.4a). Pyruvate produced from glycolysis is oxidatively dehydrogenated to form acetyl-CoA, which is further metabolized to acetate through phosphate acetyltransferase (pta) and acetate kinase (ackA). AMGs encoding these enzymes were all elevated in post-FMT samples (Supplementary Fig.4b). 3-Phospho-D-glycerate derived from glycolysis can be interconverted with 3-phosphonooxypyruvate, which is an important intermediate in the synthesis of 3-phosphoserine. The significantly increased AMG encoding cysteine synthase (cysK) in post-FMT samples may promote the conversion of 3-phosphoserine to cysteine (Supplementary Fig.5a). As a precursor of cysteine, cystathionine can be metabolized from aspartate and the process may be promoted by elevated levels of AMGs encoding homoserine dehydrogenase (hom) and homoserine O-acetyltransferase (metA) observed in post-FMT samples (Supplementary Fig.5b). Moreover, the cystathionine can be mutually transformed with homocysteine, which is methylated to form methionine by the 5-methyltetrahydrofolate-homocysteine methyltransferase (metH) and 5-methyltetrahydropteroyltriglutamate-homocysteine methyltransferase (metE). In contrast, the methionine can be converted to S-adenosylmethionine (SAMe) through S-adenosylmethionine synthetase (metK). After that, methyl group of SAMe is transferred to a range of receptor molecules by DNA (cytosine-5)-methyltransferase 1 (dcm, encoded AMG was decreased post-FMT) to generate S-adenosylhomocysteine (SAH), which is then hydrolyzed into homocysteine and adenosine by adenosylhomocysteinase (ahcY, encoded AMG was decreased post-FMT) (Supplementary Fig.4c). As one of the starting compounds of the shikimate pathway, phosphoenolpyruvate from glycolysis might be accelerated to shikimate by dehydration, cyclization and dehydrogenation through elevated AMGs encoding 3-dehydroquinate dehydratase II (aroQ) and shikimate dehydrogenase (aroE) after FMT (Supplementary Fig.6a). Chorismate, which is metabolized from shikimate by the shikimate kinase (aroK/aroL), is a key intermediate in the biosynthesis of aromatic amino acids. Among these, tryptophan synthesis might be enhanced by the tryptophan synthase (alpha chain, trpA; beta chain, trpB; encoded AMGs were increased post-FMT) (Supplementary Fig.6b). These results suggest commonalities in metabolic regulation shared among gut phageomes across FMT studies, potentially implicated in FMT induced post-FMT phageome shifts.