Megasphaera elsdenii, a Commensal Member of the Gut Microbiota, is Associated with Elevated Gas Production During In Vitro Fermentation

Gastroenterology Medicine Life Sciences Microbiology
gas production gut microbiota short chain fatty acids kidney beans sweet potatoes

Flatulence is a common occurrence in daily life, often resulting from the fermentation of undigested food components by the gut microbiota. While flatulence is generally harmless, it can lead to discomfort, bloating, and even chronic conditions such as irritable bowel syndrome (IBS). Certain foods, particularly those rich in dietary fiber like beans and sweet potatoes, are closely associated with gas production. However, the specific mechanisms by which the gut microbiota contributes to gas production remain incompletely understood.

In recent years, studies have suggested that certain key species within the gut microbiota may play a significant role in gas production. Megasphaera elsdenii is a common commensal bacterium in the gut, known for its ability to metabolize lactate and produce short-chain fatty acids (SCFAs) in ruminants. However, its role in the human gut has not been thoroughly investigated. Specifically, whether M. elsdenii is associated with intestinal gas production and its mechanisms of action during the fermentation of different foods remain unresolved. Therefore, this study aimed to explore the role of M. elsdenii in intestinal gas production, particularly during the fermentation of beans and sweet potatoes.

Source of the Paper

This paper was authored by Professor Devin J. Rose from the University of Nebraska–Lincoln and his team, including Erasme Mutuyemungu, Hollman A. Motta-Romero, Qinnan Yang, and others. The research was supported by the USDA Agricultural Research Service. The paper was accepted on December 15, 2023, and published in 2024 in the journal Gut Microbiome, with the DOI 10.1017/gmb.2023.18.

Research Process

1. Fecal Sample Selection

The research team first collected fecal samples from 30 healthy donors, screening for samples with detectable M. elsdenii (ME_D) and those without M. elsdenii (ME_ND). Ultimately, three ME_D samples and seven ME_ND samples were selected for the study. All donors had no history of gastrointestinal disorders and had not used antibiotics or probiotics in the past six months.

2. Substrate Preparation

The study selected two foods associated with gas production—kidney beans and sweet potatoes—as fermentation substrates. These foods underwent in vitro digestion and dialysis before being freeze-dried and stored for subsequent experiments.

3. In Vitro Fermentation Experiment

Freeze-dried kidney beans and sweet potatoes were subjected to in vitro fermentation with fecal microbiota. Fermentation was conducted under anaerobic conditions, and gas production was measured at 0, 24, and 48 hours. A modified fermentation medium was used to ensure the microbiota fermented in a simulated intestinal environment.

4. Gas Production Measurement

Gas production was measured by inserting a needle connected to a glass syringe into the fermentation tube. The study recorded gas volume at 24 and 48 hours and analyzed differences between samples.

5. Short-Chain Fatty Acid (SCFA) Analysis

Post-fermentation samples were centrifuged, and the supernatant was extracted for SCFA analysis. Gas chromatography was used to measure the concentrations of acetate, propionate, and butyrate.

6. Microbiota Composition Analysis

The research team extracted DNA from bacterial pellets obtained post-fermentation and analyzed the microbiota composition through 16S rRNA gene sequencing. QIIME 2 software was used to process the sequencing data, and the DADA2 algorithm was employed for sequence denoising and classification.

7. M. elsdenii Isolate Experiment

To validate the role of M. elsdenii in gas production, the research team used two M. elsdenii isolates: one from human feces (M. elsdenii 2FL 0620 M7) and another from ruminants (M. elsdenii B159). These isolates were subjected to fermentation experiments with sweet potatoes and acetate as substrates, and their gas production was measured.

Key Findings

1. Differences in Gas Production

The results showed that microbiota containing M. elsdenii (ME_D) produced significantly more gas during the fermentation of sweet potatoes compared to microbiota without M. elsdenii (ME_ND). Particularly, at 48 hours of fermentation, ME_D microbiota generated more gas from sweet potatoes than from kidney beans, while ME_ND microbiota produced more gas from kidney beans.

2. Changes in M. elsdenii Abundance

During fermentation, the relative abundance of M. elsdenii significantly increased in ME_D microbiota, reaching up to 60% in some samples. In ME_ND microbiota, M. elsdenii abundance remained low but was detectable post-fermentation.

3. Short-Chain Fatty Acid (SCFA) Production

ME_D microbiota consumed more acetate and produced more butyrate during fermentation. This was particularly evident during sweet potato fermentation, where butyrate production increased significantly. This suggests that M. elsdenii may utilize acetate for cross-feeding to produce butyrate and gas.

4. Gas Production by M. elsdenii Isolates

The M. elsdenii 2FL 0620 M7 isolate from human feces produced substantial gas from both sweet potatoes and acetate, with the highest gas production observed when both substrates were combined. In contrast, the M. elsdenii B159 isolate from ruminants produced the most gas from sweet potatoes but showed lower gas production from acetate.

Conclusions and Significance

This study is the first to systematically investigate the role of M. elsdenii in intestinal gas production, particularly during the fermentation of beans and sweet potatoes. The results indicate that M. elsdenii is an important member of the gut microbiota, significantly increasing gas production, especially during sweet potato fermentation. Additionally, M. elsdenii promotes butyrate production through acetate cross-feeding, further exacerbating gas generation.

The scientific value of this study lies in its revelation of the key role of M. elsdenii in intestinal gas production, providing new insights into the relationship between gut microbiota and food fermentation. Furthermore, the findings offer potential targets for interventions aimed at alleviating gas-related discomfort, such as modulating the gut microbiota to reduce gas production.

Research Highlights

  1. Key Discovery: M. elsdenii is a significant driver of intestinal gas production, particularly during sweet potato fermentation.
  2. Novelty: This is the first systematic study of the mechanisms by which M. elsdenii functions during the fermentation of different foods, validating the hypothesis of gas production through acetate cross-feeding.
  3. Application Value: The findings provide a scientific basis for developing interventions to address gas-related discomfort, such as modulating the gut microbiota to reduce gas production.

Additional Valuable Information

The study also found that the abundance of M. elsdenii significantly increased during fermentation, indicating its strong adaptability to the intestinal environment. Moreover, the gas production capacity of M. elsdenii isolates from human feces differed significantly from those from ruminants, suggesting that host origin may influence their metabolic characteristics.

This research offers new insights into the relationship between gut microbiota and food fermentation, laying the groundwork for future studies and applications.