Soil-derived microbiota shows potential for immune regulation

Exposure to soil or soil-like material enriched with a diverse microbial community, particularly slow growing bacteria, significantly enhances immune regulation, Sinkkonen explained at the International Scientific Association for Probiotics and Prebiotics (ISAPP) event in Cork, Ireland.

He noted that while research is in an early stage, current findings have the potential to revolutionize approaches to preventing non-communicable diseases.

Soil Microbiota​

Lack of exposure to the natural microbial diversity of the environment​ has been linked to dysregulation of the immune system​ and non-communicable diseases, such as allergies and autoimmune disorders, Sinkkonen explained the audience. 

He noted that recently, research has found that contact with soil material, rich in naturally occurring microbes, could have a beneficial immunoregulatory impact on the immune system. 

“Since effective immune regulation is essential in preventing various non-communicable diseases, ongoing trials could establish that contact with these soil-like materials may offer a preventive measure against these health issues,” Sinkkonen noted.

In one recent study published in BMC Immunology​, Sinkkonen's research team exposed mice to autoclaved and live soil powders that had the same rich microbiota before autoclaving.

The authors from Finland assessed the effect of the soil powders on the mouse immune system by analyzing different immune cell populations, gene expression in the gut, mesenteric lymph nodes and lungs, and serum cytokines.

Results showed that expression of Foxp3​—a protein involved in immune system responses—was elevated in the colons of mice exposed to autoclaved soil, while it was reduced in mesenteric lymph nodes (mLNs) in live soil-exposed animals.

Results showed that exposure to live soil powder skewed the immune system, and the authors hypothesized that it could be beneficial for inhibiting inflammation.

While they noted that the mechanism was not fully understood, they wrote that differences "may reflect the distinct immunological functionalities of different sites, or alternatively, changes in microbial antigen content during autoclavation." 

Another recent study by the same authors published in Environment International​ found that urban indoor gardening enhanced immune regulation and diversified skin microbiota​. 

The placebo-controlled double-blinded intervention study recruited healthy adults to participate in urban indoor gardening using either microbially rich or poor growing medium.

Participants were instructed to monitor, harvest, and consume produce daily, and results showed that gardening with microbially rich growing medium diversified skin microbiota and increased anti-inflammatory IL-10 levels in the blood.  

No changes in skin microbiota or blood cytokine levels were observed when a microbially poor growing medium was used.

“This biodiversity intervention trial demonstrated for the first time that urban indoor gardening has the potential to diversify the microbiota on human skin and to increase anti-inflammatory cytokine levels in plasma,” Sinkkonen explained. 

Next steps​

Sinkkonen emphasized that single or limited-strain probiotics may offer limited effects compared to the broad-spectrum microbiota found in soil. 

He said that while probiotics have shown effectiveness in addressing conditions like diarrhea, their success in preventing immune-mediated diseases has been limited. 

“The research suggests that a broad-spectrum exposure, as found in soil, is more effective in promoting immune health,” he noted.

According to Sinkkonen, soil appears to be essential for most strains at present, however, this presents questions about how best to replicate these conditions for practical applications.

He added that while current investigations are exploring whether the soil is necessary to cultivate beneficial strains, one of the primary challenges is the commercialization of these slow growing-bacterial strains.  

“Unlike fast-growing strains that can be quickly and easily cultivated, the slow growing strains present in soil require a specific substrate for growth, making their commercial production complex and time-consuming,” he said. 

“This complexity underscores the need for innovative solutions to make these beneficial microbes widely available.”