Lactic acid bacteria contribution to gut microbiota complexity: lights and shadows

The gut microbiota is a complex ecosystem shaped by interactions between microbial species and host physiology. While lactic acid bacteria (LAB) are well-known for their fermentative capabilities, their broader metabolic and physiological roles remain underexplored. Prior research has shown that LAB contribute to gut homeostasis through fermentation and adhesion mechanisms. However, the full scope of their interactions with the host and other microbes is not fully understood. This gap motivated researchers to investigate how LAB influence gut function beyond fermentation. The electrogenic processes and proteolytic systems of LAB suggest additional roles in gut signaling and metabolism. Histamine and tyramine production by LAB may affect central nervous system activity and immune responses. At the same time, some LAB synthesize bioactive compounds like GABA, which may modulate gut motility and mood. The interplay between LAB and host metabolism remains a key uncertainty in the field.

This study aimed to clarify the multifaceted roles of lactic acid bacteria in gut microbiota dynamics and host physiology. The researchers focused on how LAB maintain survival in the gastrointestinal tract through electrogenic processes and proteolytic systems. They sought to understand the molecular cross-talk between LAB and human cells, particularly in response to gut stimuli. The study also examined the dual effects of LAB metabolites on health outcomes, such as hypertension versus relaxation. Another goal was to assess the impact of LAB-derived short-chain fatty acids and conjugated linoleic acids on host metabolism. The researchers also explored the potential of LAB as antioxidant vectors through selenium fixation. By integrating biochemical and physiological data, the study aimed to provide a comprehensive view of LAB's contributions to gut health. This approach allows for a nuanced understanding of both beneficial and potentially harmful effects of LAB in the gut ecosystem.

The study reviewed existing literature on lactic acid bacteria (LAB) and their metabolic and physiological interactions with the gut. Researchers analyzed the biochemical pathways LAB use to generate ATP, including decarboxylation and deimination processes. They examined the molecular mechanisms of LAB adhesion to mucosal surfaces and immune cell activation. The team also evaluated the role of LAB in antagonizing pathogenic microorganisms through competitive exclusion. Histamine and tyramine production by LAB were assessed for their effects on the central nervous system and immune responses. The synthesis of bioactive compounds like GABA and beta-phenylethylamine was studied in relation to gut motility and mood regulation. Researchers also investigated the proteolytic systems of LAB and their role in generating antihypertensive and opioid peptides from milk proteins. Finally, the study explored the metabolic impact of short-chain fatty acids and conjugated linoleic acids on host physiology and disease risk.

Lactic acid bacteria (LAB) use electrogenic decarboxylation and deimination to maintain ATP and survive in the acidic gut environment. These processes allow LAB to buffer their surroundings, facilitating colonization of the gastrointestinal tract. LAB produce moonlight proteins in response to gut signals, promoting adhesion to mucosa and immune cell stimulation. The presence of LAB triggers specific gene expression in human enterocytes, indicating a targeted host response. LAB also exhibit antagonistic relationships with other gut microbes, contributing to their anti-infective properties. Histamine and tyramine, produced by some LAB, can cause hypertension and allergic reactions. However, other LAB synthesize GABA and beta-phenylethylamine, which may relax gut muscles and regulate mood. LAB's proteolytic systems generate bioactive peptides from milk proteins, including antihypertensive and opioid-like molecules. Short-chain fatty acids from LAB metabolism influence epithelial cell proliferation and serve as an energy source, potentially contributing to weight gain. Conjugated linoleic acids (CLA) produced by LAB have mixed effects, with some isomers reducing cancer cell viability while others lower HDL/LDL ratios and affect eicosanoid production.

The study highlights the dual roles of lactic acid bacteria (LAB) in gut microbiota and host physiology. LAB maintain survival through electrogenic processes and proteolytic systems, enabling colonization of the gastrointestinal tract. Their interactions with host cells involve specific gene expression and immune modulation, indicating a targeted molecular cross-talk. LAB antagonize other microbes, contributing to anti-infective effects. However, some LAB metabolites like histamine and tyramine may cause hypertension and allergies. Conversely, GABA and beta-phenylethylamine may have beneficial effects on gut motility and mood. LAB proteolytic systems generate bioactive peptides from milk proteins, including antihypertensive and opioid peptides. Short-chain fatty acids from LAB metabolism influence epithelial cell function and may contribute to weight gain. Conjugated linoleic acids (CLA) have mixed effects on health, with some isomers showing anti-cancer properties while others may be detrimental. The ability of LAB to fix selenium into seleno-cysteine opens new possibilities for their use as antioxidant nutraceutical vectors.