On 2025-05-19 23:28:03, user Thomas Gilmore wrote:
Undergraduate students in BI576, “Carcinogenesis”, at Boston University had the assignment of reviewing a preprint paper. This was one of the preprints that they reviewed. They provided a number of comments on the paper. The students fully acknowledge that they are not scientific experts. Nonetheless, they hope that some of their comments will be useful to the authors as they prepare their work for submission to a peer-reviewed journal. <br />
The interplay between diet, the gut microbiome, and cancer risk, particularly colorectal cancer (CRC) was a fascinating topic for us to dive into. Finding links to gut chemistry with cancer risk in C57Bl/6 mice and human colorectal cancer patients, through investigating how a Western style diet affects gut microbial composition, sulfide production, and intestinal epithelial function through a combination of murine models and a meta-analysis of human patient data, we believe laid a strong foundation. These results suggest that sulfide metabolism serves as a functional biomarker for dietary impact on CRC risk, with gene expression analyses showing diet-driven suppression of sulfide detoxification enzymes in intestinal stem cells, particularly an enrichment of Erysipelotrichaceae leads to the strong possibility of CRC association.<br />
This dual species approach strengthens the relevance of the findings. However, there were some limitations in current methodologies, such as small sample sizes and insufficient controls for geographic dietary variation. Along with providing evidence of between Erysipelotrichaceae and high sulfide concentration in the gut. Despite these caveats, the study contributes meaningfully to the growing body of literature linking nutrition, microbiome dynamics, and oncogenesis. The findings warrant further exploration into metabolic pathways influenced by diet and underscore the need for broader, better controlled human studies to confirm causative links between microbial sulfur metabolism and colorectal cancer. Below are our group's critiques of the paper.<br />
Figure 1 presents an informative and visually accessible graph, though several refinements could improve its readability and clarity. One immediate issue is the placement of axis titles and labels, which currently overlap with axis ticks on both the x- and y-axes. Ensuring a clearer separation between these elements would enhance legibility. Additionally, the bacterial names on the graph may benefit from abbreviation or reformatting to make individual taxa easier to identify. Organizing the bacteria according to taxonomic hierarchy could also aid interpretation, helping readers quickly distinguish between different microbial groups and understand their relative significance. It would be useful to explicitly note in the figure legend that bacteria from the same taxonomy are color coded similarly, making visual groupings more intuitive. Furthermore, revising the color palette to accommodate colorblind friendly options would broaden accessibility and ensure all viewers can accurately interpret the data.<br />
The accompanying discussion of Figure 1 effectively contextualizes the findings and links them back to the overarching theme of diet and microbial sulfide production. One suggested edit for clarity and consistency is to revise the phrase “Importantly, we show that” to “Importantly, we showed that,” aligning with the past tense scientific narrative. Similarly, the assertion that “diet is the strongest determinant” of gut sulfide production might be more accurately phrased as “diet is a strong determinant,” since other potential influences were not investigated in the study. Supporting this revised claim with references to other research examining factors that affect gut sulfide production would help reinforce the conclusion.<br />
Notably, the concluding sentence “Thus, we posit that sulfide production can be considered a community level functional readout of dietary sulfur nutrient input that is potentially linked to multiple effects on the mucosa, including the intestinal remodeling characterizing IBD and tumor risk” is particularly effective. It succinctly captures the relevance of the findings and articulates their broader implications for understanding how diet may influence mucosal health and disease risk. <br />
Figure 2 aims to demonstrate that Erysipelotrichaceae abundance is elevated in mice fed the NWD1 diet compared to those fed the AIN control diet. While the figure successfully communicates a statistically significant difference—supported by the inclusion of both P- and Q-values (P = 0.019917, Q = 0.025892)—its overall presentation could be improved to enhance readability and interpretability. Most notably, the use of different shapes to represent mouse sex adds unnecessary complexity, as these distinctions are not analyzed or discussed within the figure or the main text. Similarly, the use of red and blue color coding for diet groups is redundant, given the clear labeling on the x-axis. Simplifying these elements and ensuring the figure employs a colorblind friendly palette would make the data more accessible. Importantly, statistical significance is only indicated in the caption, not visually within the figure itself. Including an asterisk or bold text to highlight the difference in NWD1 would make this clearer to readers. Additionally, the figure would benefit from stating the sample size directly, including clarification that both sexes were equally represented. Overlaying a median bar or converting the scatter plot to a box plot would also improve visual clarity, particularly where individual data points overlap.<br />
Although the inclusion of the P- and Q-values is appreciated, the caption does not describe how these values were calculated, nor does it provide adequate information on sample size, data collection methods, or statistical models used. For example, while the MaAsLin2 model incorporated "Sex" as a fixed effect, the figure and accompanying text do not explore whether an interaction exists between sex and diet—a potentially informative variable. This omission is particularly notable given the use of sex-based symbols in the graph. In terms of content relevance, the data in Figure 2 might be more appropriately placed in the supplementary material, particularly since Figure 3 appears to carry the narrative forward more directly. Supplemental figures like Figure 5, which show trends in microbial abundance over time for individual mice, are valuable for highlighting inter individual and potential sex-based variation. However, more detail should be provided on how bacterial groups were selected for inclusion, as well as on the decision-making process for which data were elevated to the main figures. Finally, while the use of standardized sequencing and DNA extraction methods (e.g., PowerFecal kit, V4-V5 region) strengthens methodological consistency, the absence of a control group to account for batch effects (such as collection date or sequencing run) is a limitation that should be addressed in future studies.<br />
In Figure 3 the study presents compelling associations between dietary intake, gut microbiota, and colorectal cancer (CRC) risk, yet several aspects warrant deeper scrutiny and refinement. Notably, the experimental design utilized small cohorts, with only eight mice per diet group (n = 8), which limits statistical power and the generalizability of the findings. A central biochemical focus of the study is hydrogen sulfide (H₂S), which the authors implicate in mucosal damage. The original phrasing, “Sulfide has been shown to damage the mucosa by cleaving disulfide bonds found in mucus and has been linked with diseases with marked mucosal damage,” can be more clearly articulated as: “Sulfide cleaves disulfide bonds in mucosa, damaging the tissue and linking it to diseases with marked mucosal damage.” However, while this biochemical mechanism is plausible, the study lacks direct experimental evidence of mucosal degradation or impaired mucosal function, such as histological analysis or barrier function assays, to substantiate this claim within the context of their model.<br />
Furthermore, the relationship between Erysipelotrichaceae abundance and sulfide production remains correlative rather than causal. Although the meta-analysis shows an increased prevalence of Erysipelotrichaceae in CRC patients and mice on a Western style diet, no mechanistic data address whether this microbial family is directly responsible for enhanced sulfide synthesis. The current framing risks overstating the significance of Erysipelotrichaceae without isolating its metabolic role. Additionally, the claim that sulfide is a sufficient marker for mucosal damage and CRC risk oversimplifies the complex pathophysiology involved. Line 412-413 should be removed to avoid this overgeneralization, while retaining the more nuanced correlation stated in Line 411. Lastly, the diets used in the study differ across multiple nutritional variables, including fat, fiber, calcium, vitamin D, and sulfur containing amino acids. The conclusion attributing increased sulfide production to a single component overlooks this complexity. A more accurate interpretation would acknowledge the composite nature of the Western style diet and the need for controlled studies isolating specific dietary variables.<br />
Figure 4 provides valuable insights into how dietary interventions affect the expression of mitochondrial enzymes involved in sulfide metabolism, yet several improvements would enhance the clarity and interpretability of the data. Figure 4a offers a helpful schematic that illustrates the localization of sulfide detoxification enzymes—such as SQR (Sqrdl), ETHE1, SUOX, and TST—within mitochondrial structures and identifies the directionality of reactant flow. However, the figure would benefit from a more thorough introduction describing each enzyme’s specific role in sulfide detoxification and the broader significance of this pathway. Without this context, it is unclear why all four enzymes are studied, especially since ETHE1, SUOX, and TST appear to serve overlapping functions. Furthermore, the inconsistent labeling of sulfide quinone reductase-like protein referred to as SQR in Figure 4a and Sqrdl in Figure 4b and the text should be standardized across the manuscript to avoid confusion. The visual consistency between Figures 4a and 4b also requires attention, particularly the shading conventions, which imply relationships between data that are not explicitly connected.<br />
Figure 4b effectively illustrates differential gene expression between diet groups, demonstrating that expression of Ethe1, Suox, and Tst is significantly altered in response to the NWD1 diet. However, the figure would be clearer if significance were marked with asterisks above the relevant bars rather than listing precise p-values, which could instead be moved to the figure caption or results section. Importantly, Sqrdl expression did not show a significant difference, which raises interpretive questions. Including a hypothesis in the discussion about why Sqrdl expression was unchanged—despite the other enzymes showing significant variation—would help contextualize the data. Additionally, the discussion of these results would be strengthened by addressing why the observed changes in Ethe1, Suox, and Tst expression are biologically meaningful and warrant further study, as briefly noted in the concluding sentence of that section. Greater emphasis on the relevance of sulfide metabolism in intestinal stem cells could also help bridge the mechanistic findings to broader health implications, such as inflammation or tumor development.<br />
The associated methods section also lacks critical detail. The repeated mention of “bulk RNAseq” without a quantitative description (e.g., read depth, sample pooling strategy) is insufficient and should be clarified rather than deferring entirely to the Gene Expression Omnibus. Additionally, it is unclear how mRNA expression was normalized in the analysis—a fundamental detail that should be explicitly stated either in the methods or the figure caption. Lastly, phrasing such as “at sacrifice” could be revised to more standard terminology like “at the time of euthanasia” to maintain scientific professionalism. Addressing these issues would greatly enhance the transparency, rigor, and impact of the study’s findings.<br />
Figure 5 provides a valuable cross-species summary of the association between Erysipelotrichaceae taxa and colorectal cancer (CRC), but several refinements would improve its clarity, consistency, and interpretability. In Figure 5A, the addition of an x-axis label—specifically identifying it as the “AUC Score”—would aid reader comprehension, particularly for those unfamiliar with this metric. To further clarify the analysis, the figure caption or discussion should define the AUC (Area Under the Curve) score, explaining that scores below 0.5 may indicate taxa enriched in CRC cases, but that statistical significance is determined by whether the 95% confidence interval crosses the 0.5 midline. Highlighting this explicitly in both the figure and caption would prevent misinterpretation. Visually, increasing the size and contrast of the asterisks denoting significance—and using colorblind friendly alternatives—would enhance accessibility. The midline at 0.5 should be made more prominent to emphasize its role as a visual reference for enrichment or depletion in CRC.<br />
In Figure 5B, the rationale behind using cysteine desulfhydrase genes as markers for sulfide production should be more thoroughly explained in the caption or Discussion. A brief explanation of their role in hydrogen sulfide synthesis would provide essential context, especially since the paper hinges on microbial sulfide metabolism as a mechanism linking diet and disease. Terminological clarity is also needed: the phrase “presence/absence” should be replaced with “presence or absence” for proper usage, and minor grammatical errors (e.g., “cysteine desulfhydrase genes”) should be corrected. Consistency between panels A and B would also enhance the reader’s experience. This includes presenting the bacterial species in the same order along the y-axis, capitalizing figure labels (“Figure 5A” and “Figure 5B”), and starting the caption for each panel on a separate line. Shortening bacterial species names (e.g., using D. fastidiosa instead of Dilemma fastidiosa) could make the y-axis more readable without sacrificing clarity.<br />
Overall, these changes would not only improve the figure’s visual clarity but also support a more nuanced understanding of the results. Aligning terminology, improving visual accessibility, and strengthening the interpretive context particularly regarding the AUC metric and sulfide related gene markers would make Figure 5 more informative and persuasive within the broader narrative of dietary influence on gut microbiota and CRC risk.<br />
Lastly our group proposed several edits aimed at improving the clarity, consistency, and grammatical precision of the manuscript. Key terms such as “AUC” (pg. 16), “Lgr5hi ISCs” (pg. 5), and “IACUC” (pg. 6) should be defined upon first use to aid reader comprehension. We also recommended standardizing terminology particularly by using “Western style diet” consistently throughout the text. Edits included grammatical corrections (e.g., appropriate comma placement, hyphenation, and noun verb agreement), as well as restructured sentences to enhance readability and provide necessary methodological details. Several phrases were revised to reduce ambiguity and better support the study's conclusions.<br />
● Pg 2, line 47: “Western-style diets, characterized by high fat and protein content and low micronutrient levels, promote...” (added commas for clarity).<br />
● Pg 2, lines 52–53: “NWD1 is a purified Western-style diet that induces sporadic intestinal and colonic tumors in the absence of genetic predisposition or carcinogen exposure.”<br />
● Pg 2, line 69: “...human CRC patients, suggesting microbial signatures of CRC and gut ecosystem...” (clarified phrase structure).<br />
● Pg 3, line 80: “Colorectal cancer (CRC) is the second leading cause of cancer deaths and the third most common cancer worldwide.” (deleted unnecessary comma).<br />
● Pg 3, lines 84–85: Added a comma: “...mortality in both human and mouse studies, and can shape...”<br />
● Pg 3, line 89–90: Clarified structure: “...with early and late-stage CRC, but how diet, microbes, and gut chemistry influence cancer development is not well understood.”<br />
● Pg 3, line 91: Changed to “microbially derived” (removed incorrect hyphen).<br />
● Pg 3, line 93: Clarified chemical notation: “sulfide (including H₂S, HS⁻, and S²⁻).”<br />
● Pg 3, line 96: “sulfur-containing amino acids” (standardized compound adjective).<br />
● Pg 4, line 112: “...is NWD1, which was formulated...” (added comma for flow).<br />
● Pg 4, line 117: “...tumors in wild-type mice, which rarely, if ever, develop...” (added second comma).<br />
● Pg 4, line 123: “...donor nutrients; and increased fat content that reflects levels linked to increased CRC risk.” (refined punctuation).<br />
● Pg 4, lines 115–118: Reworked sentence for clarity: “Feeding mice NWD1 accelerates and amplifies intestinal and colon tumors in many genetic models and is unique in reproducibly causing sporadic tumors in wild-type mice, which rarely develop such tumors on other diets.”<br />
● Pg 5, line 130: Suggested defining “Lgr5hi ISCs” on first use.<br />
● Pg 6, line 153: Recommended defining “IACUC” (Institutional Animal Care and Use Committee).<br />
● Pg 8, line 191: “Freshly voided fecal pellets were collected from individual mice...” – suggested specifying the collection timing for clarity.<br />
● Pg 8, line 201: “...using a –p-trim length of 301, and a feature table was created.” (added optional comma for smoother reading).<br />
● Pg 9, lines 214–215: “...single-cell suspensions were prepared and sorted by FACS...” – clear and concise.<br />
● Pg 11, line 275: “(Supplementary Fig. 4, 5)” – recommend using full form for clarity, depending on journal style.<br />
● Pg 12, line 284: “Samples from male mice are represented by open triangles; female mice by filled dots.” (revised for parallel structure).<br />
● Pg 13, line 310: “...control AIN76A diet or NWD1, a Western-style, colorectal cancer-promoting diet, from weaning.” (added comma for clarity).<br />
● Pg 13, line 311: “A total of three female mice were fed AIN, and three female mice were fed NWD1.” (deleted redundant “3”).<br />
● Pg 14, line 323: “...knockout of a key gene downregulated by NWD1...” (moved line break and cleaned structure).<br />
● Pg 14, line 329: Deleted extraneous comma after “(Sqrdl)”.<br />
● Pg 16, lines 367–368: Suggested moving AUC definition earlier in the text (e.g., pg. 9) and clarified phrasing.<br />
● Pg 16, line 372: Changed “presence/absence” to “presence or absence” for grammatical accuracy.<br />
● Pg 16, line 373: Corrected to “cysteine desulfhydrase genes” (fixed redundancy).<br />
● Pg 17, lines 388–390: Streamlined sentence for clarity: “...associated with CRC in a nine-study, 1,650-sample meta-analysis of human colorectal cancer and control metagenomes.”<br />
● Pg 17, lines 391–393: Removed line break and clarified phrasing.<br />
● Pg 18, line 417: “...within four days of the shift to NWD1.” – removed article “the” before “NWD1”.<br />
● Pg 19, lines 446–448: Revised for grammar and punctuation: “...dynamics of dietary alterations in bacteria; the microbial metabolite, sulfide; and gut epithelial gene expression. As such, we acknowledge several limitations...”<br />
● Pg 19, lines 448–449: Sentence fragment—needs completion or merger with another sentence.<br />
● Pg 19, lines 453–455: “...cannot distinguish whether the association of Erysipelotrichaceae with CRC patients...” – clarify structure.<br />
● Pg 20, lines 455–456: Removed redundant “of”: “...is a consequence of consuming a Western diet.”