Megasphaera is a genus of Gram-negative anaerobic cocci bacteria. These obligate anaerobes thrive in oxygen-free environments and are found in various biological systems and hosts.
Where Megasphaera Lives
Megasphaera species are commonly found in the digestive tracts of many animals, including humans. In ruminants like cattle and sheep, Megasphaera elsdenii is a prominent inhabitant of their rumen. Its anaerobic conditions and rich fermentable substrates provide an ideal environment.
Megasphaera species have been isolated from various parts of the human body, including the upper digestive tract (tongue dorsum, tonsils, saliva) and the human gut. Species like Megasphaera indica and Megasphaera massiliensis are identified in fecal samples. These anaerobic areas create suitable living conditions.
Megasphaera species have been detected in the female reproductive tract, specifically in the human vagina. Two vaginal phylotypes, Megasphaera phylotype 1 (MP1) and Megasphaera phylotype 2 (MP2), have been characterized there.
The Work of Megasphaera
Megasphaera species ferment compounds into short-chain fatty acids (SCFAs). A notable function, especially for Megasphaera elsdenii, is lactate conversion. This bacterium metabolizes lactate into volatile fatty acids (VFAs) like propionate, butyrate, and acetate, often via the acrylate pathway.
Megasphaera elsdenii uniquely utilizes both D- and L-lactate isomers, facilitated by its lactate racemase enzyme. This efficient lactate clearance is significant in ruminants. In cattle and sheep, high-grain diets can lead to lactic acid overproduction and a drop in rumen pH; M. elsdenii helps prevent ruminal acidosis by consuming this excess lactate.
In the human gut, Megasphaera species contribute to SCFA production. For instance, Megasphaera indica can interact with Bifidobacterium species. Bifidobacterium breaks down complex carbohydrates into lactate, which Megasphaera then utilizes to produce butyrate. These SCFAs benefit host health, providing energy to gut cells, supporting immune function, and reducing inflammation.
Beyond lactate metabolism, some Megasphaera species have other roles. Megasphaera massiliensis, found in the human digestive tract, produces pentanoate, an SCFA. Research suggests pentanoate can influence immune cells, potentially enhancing their ability to combat tumors.
Understanding High Megasphaera Levels
Elevated Megasphaera levels often link to dietary changes or shifts in the microbial community. In ruminants, increased Megasphaera elsdenii abundance commonly results from high-concentrate or grain-based diets. These diets lead to rapid sugar fermentation, causing a surge in lactic acid and a decrease in rumen pH, conditions where M. elsdenii thrives.
In ruminant health, high Megasphaera elsdenii levels are generally beneficial. This bacterium is a promising direct-fed microbial for mitigating subacute ruminal acidosis. M. elsdenii helps stabilize rumen pH and prevent acidosis by converting excess lactic acid into propionate, butyrate, and acetate.
Increased M. elsdenii in ruminants improves feed efficiency and animal performance. Studies show supplementation can lead to enhanced nutrient utilization, increased solid feed intake in calves, and greater average daily gain. This bacterium helps accelerate cattle adaptation to high-concentrate diets and may reduce digestive issues like diarrhea and bloat.
In humans, elevated Megasphaera levels have complex implications. In the oral cavity, increased Megasphaera abundance associates with dental caries. In the vaginal microbiome, specific Megasphaera phylotypes (MP1 and MP2) link to bacterial vaginosis (BV) and trichomoniasis. High vaginal Megasphaera proportions correlate with elevated vaginal pH, increased risk of sexually transmitted infections (including HIV), and may contribute to spontaneous preterm birth.
Conversely, in the human gut, Megasphaera generally contributes to a balanced environment. Low Megasphaera abundance in infant stool has been associated with diarrheal symptoms during Cryptosporidium infection, suggesting a protective role against acute diarrhea. However, some research indicates Megasphaera elsdenii can correlate with elevated gas production during in vitro fermentation of non-digestible carbohydrates (e.g., kidney beans, sweet potatoes).