Álvaro García
Bacillus subtilis is a rod-shaped, Gram-positive bacterium found in the soil and the gastrointestinal tract of ruminants and humans. Since its discovery in 1835 by Christian Gottfried Ehrenberg, it has been extensively studied for its ability to form tough, protective endospores, allowing it to withstand extreme environmental conditions.
This bacterium is also recognized for its probiotic properties, balancing the gut microbiota, boosting the immune system, and aiding in digestion. Probiotics or direct fed microbials containing Bacillus subtilis are often recommended for preventing and treating gastrointestinal disorders such as irritable bowel syndrome and inflammatory bowel disease in humans. Moreover, studies have shown that it can produce antibiotics like bacitracin, which is effective against a range of pathogenic bacteria. The industrial applications of B. subtilis are also remarkable. It is widely used in the production of enzymes and biochemical products, including amylase, protease, and lipase, essential in various industries ranging from food and beverage to pharmaceuticals and detergents. The bacterium’s ability to secrete large quantities of enzymes has made it a staple in biotechnological processes.
Bacillus subtilis and the environment
One of the most significant benefits of Bacillus subtilis lies in its role in agriculture, enhancing soil health through several mechanisms. It suppresses soil-borne pathogens by producing antimicrobial compounds, promoting a healthier root environment. As a Plant Growth-Promoting Rhizobacteria, it secretes phytohormones that boost root and shoot growth. It aids in nutrient cycling by decomposing organic matter and solubilizing phosphate, making nutrients more accessible to plants. Its biofilm formation improves soil structure, enhancing water retention and aeration. Additionally, it induces systemic resistance in plants, strengthening their defense against various pathogens. B. subtilis also contributes to bioremediation by degrading soil contaminants, reducing the need for chemical inputs and promoting sustainable agriculture. This eco-friendly approach to pest control and soil enhancement reduces the need for chemical fertilizers and pesticides, making farming more sustainable.
Recent research suggests it could also have beneficial effects on curbing greenhouse gas emissions when fed to cattle as a direct-fed microbial. A study conducted by the Department of Animal Sciences at the University of Florida (Sarmikasoglou et al. 2024) investigated how Bacillus subtilis supplementation influenced ruminal fermentation in cows. The researchers used rumen fluid from mid-lactation Holstein cows fed a total mixed ration (TMR). To assess ruminal fermentation characteristics they collected rumen fluid samples three hours after the morning feeding and analyzed it for pH, lactate, volatile fatty acids (VFAs), ammonia nitrogen (NH3-N), and total gas production. The study employed three inoculums: a control of microcrystalline cellulose, treatment 1 of 10 billion B. subtilis + microcrystalline cellulose, and treatment 2 of 60 billion B. subtilis + microcrystalline cellulose, tested in diets for early lactation, mid-lactation, and dry cows.
Results showed that Bacillus subtilis inclusion significantly affected rumen pH, NH3-N concentration, lactate concentration, and total VFA concentration over time. Diets supplemented with microcrystalline cellulose (MCC) exhibited higher pH and lower NH3-N and lactate concentrations compared to those with B. subtilis.
Interestingly, Bacillus subtilis supplementation influenced the proportions of various VFAs, indicating its complex impact on ruminal fermentation. Iso-valerate and caproate molar proportions were significantly influenced by both inoculum and diet, with higher inclusion rates of B. subtilis showing higher molar proportions. Caproate, also known as hexanoate, is a six-carbon, short-chain fatty acid (SCFA), a VFA produced during the fermentation of dietary fibers by microorganisms in the gastrointestinal tract. The findings on VFAs production aligned with previous research, showing changes in acetate, butyrate, valerate, and iso-valerate concentrations with B. subtilis supplementation. Moreover, total methane production was significantly lower with B. subtilis supplementation in specific diet types, suggesting an anti-methanogenic potential, possibly through promoting propionate production.
Bacillus subtilis is a versatile bacterium that offers a wide spectrum of benefits across various areas. Outside of the animal it contributes to soil enhancement, promoting fertility, suppressing pathogens, and aiding in inorganic matter decomposition. This eco-friendly approach reduces reliance on chemical inputs, offering a sustainable path towards enhanced crop yield and quality. When used as a direct-fed microbial, it promotes optimal digestion, nutrient absorption, and immune function by supporting healthy gut microbiota. Its enzymatic enhancement, including amylase, protease, and lipase, improves nutrient digestibility and overall gut health. Additionally, B. subtilis exhibits antimicrobial properties, inhibiting harmful pathogens and improving gut defense against infections. As demonstrated in recent research findings, it also has the capacity to reduce methane production in ruminants, underscoring a potential contribution to mitigating agricultural greenhouse gas emissions.
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