Bugs in Your Stomach

By Leighton Pu 

Microbes—a constellation of bacteria, viruses, fungi— typically exist on the scale of micrometers. These tiny organisms are everywhere and constantly go undetected by the naked human eye.But despite their less-than-impressive size, microbes can have an incredibly profound impact on public health. Some of the most devastating diseases have been caused by microorganisms. Bubonic plague famously wiped out millions of people in Europe, Asia, and Africa in the 14th century. More recently, SARS-CoV-2 has made a global impact, caused millions of deaths, and placed enormous pressure on public health systems. 

But not all microbes are bad. High levels of certain strains of Prevotella bacteria combined with low levels of certain Bacteroides bacteria strains in the human gut, for example, have been shown to increase an individual’s success in weight loss. As such, microbial communities can have profoundly good and devastatingly bad impacts on human physiology.

This stands true for the relationship between gut microbiota and cancer. Some gut microbes are known to cause certain cancers, one famous example being Helicobacter pylori and its role in causing gastric cancer. However, the role of bacteria within the context of the cancers they’re associated with is unclear. One idea posits that as a cancer progresses, cancer cells expend the oxygen in their microenvironment, creating a more anaerobic environment ripe for bacterial infection. A different model hypothesizes that bacterial infection of gut mucosa results in tumor formation through an accumulation of DNA damage, including mutations in tumor suppressor genes and oncogenes.

Though gut microbiota have the potential to cause or exacerbate cancers, gut microbiota can also help fight against cancers. Studies have shown that altering gut microbiota in mice has led to anti-tumor immunity and decreased carcinogenesis in mice. Changing human gut microbiota to benefit cancer patients has also shown promise, as modulation of the gut microbiome has been found to impact patients’ response to treatment. As such, current work is being done to put together methods of gut microbiota modulation in order to positively influence cancer patient treatment responses.

Logically, a better understanding of gut microbiota-cancer interactions is necessary for the advancement and development of cancer treatments and the upward push of cancer treatment efficiencies. However, the complexity of the gut microbiome and its interactions with host cells is a large barrier in front of the road to advanced treatments involving gut microbiota.  Biological interactions are generally largely governed by stochasticity, or randomness. The individual dynamics of microbiota in space and time introduces another layer of complexity. The combined effects of stochasticity and spatiotemporal dynamics of the gut microbiome will exacerbate the challenges facing researchers.

Though much is unknown about the reasons behind the interplay between the human gut microbiome and cancer, current microbial methods are already being studied for their viability in affecting positive cancer therapy responses. One such method under study is the poop pill, a method that collects and transforms fecal matter from patients who responded well to cancer therapy into a pill.

While microbes aren’t impressive in size, they have power as collectives. Certain compositions of microbiota are associated with certain diseases and many facets of host biology are differentially impacted by different microbiota compositions. Despite poor understanding of gut microbiome-cancer dynamics, multiple methods are being constructed to enhance how we deal with cancer. Through continued work on establishing the link between intestinal microbiota and cancer, more appealing forms of cancer treatment may become available in the future.

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