Megamonas

Overview

Megamonas is a genus of obligate anaerobic, Gram-negative bacteria in the family Veillonellaceae (class Negativicutes, phylum Firmicutes). The type species is Megamonas hypermegale, with M. funiformis also well-characterized. It is a common member of the human gut microbiota — particularly abundant in Asian populations — and is a significant carbohydrate fermenter producing propionate and valerate as primary short-chain fatty acid end-products [1].

What makes Megamonas notable in the WikiBiome context is its contradictory directionality across conditions: enriched in some diseases, depleted in others, with no simple "good vs. bad" classification. This context-dependence makes it a useful marker for understanding disease-specific ecological shifts rather than a universal indicator of health or dysbiosis.

SCFA Production Profile

Unlike the dominant butyrate producers (faecalibacterium prausnitzii, roseburia), Megamonas primarily produces propionate and valerate:

  • Enrichment in constipated ASD children was associated with elevated propionate levels [1].
  • Enrichment in ASD more broadly was associated with elevated valeric acid [2].
  • M. funiformis emerged as an indicator of healthier dietary patterns in ASD children, suggesting its metabolic role may be diet-dependent [3].

The propionate connection is significant — propionic acid at elevated concentrations has been linked to ASD-like behavioral changes in animal models, while at normal concentrations it supports colonocyte health and immune regulation. The dose-response and context may determine whether Megamonas enrichment is beneficial or pathological.

Conditions Associated

Enriched

  • Autism spectrum disorder (4 independent studies): Consistently overrepresented in ASD children across Chinese cohorts. Associated with elevated valeric acid [2] and elevated propionate in constipated ASD [1]. Functional profiling associates with SCFA production and metabolic alterations [4]. However, M. funiformis was also an indicator of healthier diet patterns in ASD, complicating the pathological narrative [3].
  • Hashimoto's thyroiditis: Increased alongside decreased Bifidobacterium and Klebsiella, part of a consistent HT dysbiosis pattern [5]. Significant genus-level differences with gender-specific and hormone-regulated patterns [6].
  • Prostate cancer: Men with high serum testosterone (>455 ng/dL) showed increased Megamonas (r=0.46, p=0.009), suggesting a testosterone-microbiome axis [7].

Depleted

  • Graves' disease: Both GD and HT groups had lower Megamonas vs. healthy controls (Kruskal-Wallis significant) [8]. Consistent reduction across thyroid diseases [9].
  • Thyroid cancer: Decreased alongside Roseburia and Bacteroides [10] [9].
  • Heart failure: Depleted in both decompensated and compensated HF vs. controls (P<0.001) [11].
  • Colorectal adenoma/cancer: Healthy microbiome characterized by preponderance of Megamonas and Sphingobium; depleted in adenoma and CRC progression [12].

Other Associations

  • Schizophrenia: Listed as a dominant genus in schizophrenia patients alongside Faecalibacterium, Ruminococcus, and Akkermansia [13].
  • Chronic kidney disease: Abundance positively correlated with cognitive performance (attention, executive function) in hemodialysis patients [14].
  • Male reproductive function: Implicated in reproductive dysfunction signatures [15].

The Thyroid Paradox

The most striking pattern is the contradictory directionality within thyroid diseases: Megamonas is enriched in Hashimoto's thyroiditis but depleted in Graves' disease and thyroid cancer. Both are autoimmune thyroid conditions with distinct immunological mechanisms (Th1-dominant destruction in HT vs. stimulatory autoantibodies in GD). The divergent Megamonas patterns may reflect:

  1. Different immune environments selecting for different ecological niches — HT's chronic destruction may create conditions favoring Megamonas carbohydrate fermentation, while GD's stimulatory state does not.
  2. Hormonal influence — thyroid hormone levels differ dramatically (hypothyroid in HT, hyperthyroid in GD), and Megamonas shows gender-specific and hormone-regulated patterns [6].
  3. The testosterone connection — the prostate cancer finding (Megamonas correlated with testosterone, r=0.46) [7] suggests hormonal regulation of this genus, which could explain thyroid hormone-dependent shifts.

This contradiction needs resolution by future studies measuring Megamonas alongside thyroid hormone panels and immune markers simultaneously.

Ecological Role

Megamonas occupies a specific niche as an obligate anaerobe fermenting complex carbohydrates to propionate and valerate. Its depletion in heart failure, CRC, and thyroid cancer — and its association with cognitive function in CKD and healthy diet patterns in ASD — suggests that under normal conditions it contributes to a healthy fermentative ecosystem. Its enrichment in ASD and HT may reflect compensatory overgrowth when other fermenters are displaced, or it may directly contribute to pathology through excess propionate production.

Cross-References

References (15)

  1. Jianquan He, Xiuhua Gong, Bing Hu et al. (2023). He 2023 — Altered Gut Microbiota and Short-Chain Fatty Acids in Chinese Children with Constipated Autism Spectrum Disorder. Scientific Reports. doi:10.1038/s41598-023-46566-2
  2. Simeng Liu, Enyao Li, Zhenyu Sun et al. (2019). Liu 2019 — Altered Gut Microbiota and Short Chain Fatty Acids in Chinese Children with Autism Spectrum Disorder. Scientific Reports. doi:10.1038/s41598-018-36430-z
  3. Yuqi Wu, Oscar Wong, Sizhe Chen et al. (2025). Wu 2025 — Distinct Diet-Microbiome Associations in Autism Spectrum Disorder. Nature Communications. doi:10.1038/s41467-025-67711-7
  4. Wenlin Deng, Siqi Wang, Fang Li et al. (2022). Deng 2022 — Gastrointestinal Symptoms Have a Minor Impact on Autism Spectrum Disorder and Associations with Gut Microbiota and Short-Chain Fatty Acids. Frontiers in Microbiology. doi:10.3389/fmicb.2022.1000419
  5. Mendoza-Leon MJ, Mangalam AK, Regaldiz A et al. (2023). Mendoza-Leon et al. 2023 — Gut Microbiota Short-Chain Fatty Acids and Their Impact on the Host Thyroid Function and Diseases. Frontiers in Endocrinology. doi:10.3389/fendo.2023.1192216
  6. Liu J, Qin X, Lin B et al. (2022). Analysis of gut microbiota diversity in Hashimoto's thyroiditis patients. BMC Microbiology. doi:10.1186/s12866-022-02739-z
  7. Shaun Trecarten, Michael A. Liss, Jill Hamilton-Reeves et al. (2025). Trecarten 2025 — Obesity, Dietary Interventions and Microbiome Alterations in Prostate Cancer. Frontiers in Immunology. doi:10.3389/fimmu.2024.1448116
  8. Zhao H, Yuan L, Zhu D et al. (2022). Alterations and Mechanism of Gut Microbiota in Graves' Disease and Hashimoto's Thyroiditis. Polish Journal of Microbiology. doi:10.33073/pjm-2022-016
  9. Fang L, Ning J (2024). Fang & Ning 2024 — Recent Advances in Gut Microbiota and Thyroid Disease: Pathogenesis and Therapeutics. Frontiers in Cellular and Infection Microbiology. doi:10.3389/fcimb.2024.1465928
  10. Wang M, Zhu Y (2025). Wang & Zhu 2025 — Gut Microbiome Versus Thyroid Cancer: Association and Clinical Implications (Review). Oncology Letters. doi:10.3892/ol.2025.15114
  11. Tomohiro Hayashi, Tomoya Yamashita, Hikaru Watanabe et al. (2019). Gut Microbiome and Plasma Microbiome-Related Metabolites in Patients With Decompensated and Compensated Heart Failure. Circulation Journal. doi:10.1253/circj.CJ-18-0468
  12. Saito K, Koido S, Odamaki T et al. (2019). Metagenomic Analyses of the Gut Microbiota Associated with Colorectal Adenoma. PLOS ONE. doi:10.1371/journal.pone.0212406
  13. Li S, Song J, Ke P et al. (2021). The Gut Microbiome is Associated with Brain Structure and Function in Schizophrenia. Scientific Reports. doi:10.1038/s41598-021-89166-8
  14. Qiuyi Gao, Dianshi Li, Yue Wang et al. (2024). Gao et al. 2024 — Intestinal Flora and Cognitive Function in Maintenance Hemodialysis Patients. Aging Clinical and Experimental Research. doi:10.1007/s40520-023-02645-y
  15. Shuya Lv, Jingrong Huang, Yadan Luo et al. (2024). Lv 2024 — Gut Microbiota Is Involved in Male Reproductive Function: A Review. Frontiers in Microbiology. doi:10.3389/fmicb.2024.1371667

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