How variations in bacterial composition of gut flora can influence health outcomes

Microbes in the News 2

Article & Link

Same Microbe, Different Effect


This article discusses a study written by two scientists, Dr. David Zeeli and Dr. Tal Korem. These researchers created an algorithm designed to identify the variations in flora makeup across human gut microbiomes.   They ran tests on an Israeli group of 900 individuals and then formed a partnership with some Dutch researchers to identify variants in a second population. They found that most of the same variant groups were present in each population, regardless of the differences in the makeup of the two populations. They identified variants within the groups and correlated the presence of certain microbes with patterns in health outcomes. More research is being conducted in support of the idea that there is a strong link between the health and composition of our gut flora and our overall health. This study utilized an approach for analyzing the biomes that will allow scientists to closely examine this suggested linkage.


In class we discussed how there are a few recognizable and uniquely composed groups of gut flora that make up the majority of variation in composition of gut bacteria across human microbiomes. The article covered a study delving into uncovering how those groups are identified, and how correlations can be drawn using their method in order to dissect differences in gut microbes and the impacts those variations have on health outcomes. They also discuss the mechanisms by which these variations arise, such as gene transfer which we also covered in class.


Critical Analysis

I thought that this study did a great job of breaking down a complicated study into bite size chunks that are easy to understand. The article gave an example from the research which described the relationship between a certain microbial species present and waist sizes. The mechanism behind this correlation appears to be that the group of individuals with smaller waist sized have microbiomes containing a certain microbe that is able to turn sugars into a substance called butyrate that has a positive effect on the metabolism. This is an example of a pathway that has a benefit for the host individual. One can see, through this example, how the mechanisms of variants of bacteria can have significant effects on health.

A2: The Link Between Gut Bacteria and Mental Well Being

Science Magazine, Published February 4, 2019.


After a study of mice suggested that the composition of gut microbes can have an affect on behavior, scientists In Europe conducted several relatively large human studies to attempt discover a link between gut bacteria and mental health conditions in humans. It was found that the gut microbiomes of depressed people lacked two strains of bacteria that were present in the non-depressed groups. One of the strains absent in those with depression was found to have a pathway related to dopamine, more research is needed to understand the extent of the relationship.


In class we discuss the overwhelming presence of microbes and how they affect processes such as the breakdown of organic and inorganic materials. We also discuss how intertwined the lives of humans are with that of bacteria. Many of our bodily functions, including digestion, are ruled by bacteria. This study is an application of the knowledge of bacteria breakdown and production of certain substrates and how those processes interact with human function.

Critical Analysis:

As someone who has experimented with natural remedies for mood disorders, I found myself pulled towards this subject. I am fascinated by the fact there was a clear difference in the composition of the gut microbes in individuals exhibiting depressive symptoms versus those who did not. I wonder which direction the relationship goes. If depression creates an environment in which these bacteria cannot prosper, or if the lack of these bacteria may be in part responsible for depressive symptoms. I think that the article successfully conveyed the findings of the studies in a way that the general public can understand. I think the author was responsible in that she presented the factual information, made connections to other studies, and presented a conclusion that supports more research being done before a causal link can be defined.



I wonder how the long term use of antibiotics affects the health of the gut microbiome?