SUMMARY: After looking at the fecal samples of 30 autistic children and 20 neurotypical children, researchers found that the autistic group had more instances of constipation, higher valeric acid (a type of short chain fatty acid), lower butyric acid, and less biodiversity in their gut microbiota. Both alpha and beta diversity were analyzed; while alpha diversity didn’t show many differences, beta diversity showed how the species differed between autistic versus neurotypical groups. Consistent with other studies, Lactobacillus species were low in autistic children. Since different types of bacteria (aerobic/anaerobic) produce different types of fatty acids, the correlation here is that the change in bacteria will change the SCFA products. Different SCFA can have different effects on the immune system and the brain via the “microbiome-gut-brain axis”. For example, propionic acid causes more inflammation and looser junctions in the blood brain barrier (BBB) whereas butyric acid is anti-inflammatory and creates tighter junctions in the BBB.
LESSON COMMENTS: The last section of the results can be used to talk about the different ways microbiota are sequenced (looking at the difference between alpha and beta diversity). You can compare this study to other microbiota studies. A good starting discussion question could be: If diet affects gut microbiota, could the inconsistencies of microbiota studies be attributed to diet and culture? This study was conducted on Chinese children, so while some aspects were consistent, there were also inconsistencies in the results that are addressed in the discussion section.
The different types of short chain fatty acids and their molecular structures can be compared in a chemistry class. How does the change in their structures affect their function on a biological scale?
The anaerobic bacteria mentioned in this paper can also be used as an example in class to discuss the products of anaerobic respiration. In most textbooks, lactic acid is used as an example, but this paper should allow students to compare the other acids produced (the SCFA’s) in the human gut. These SCFAs can also be connected to cellular respiration as colon epithelial cells (colonocytes) absorb and metabolize SCFAs such as butyric acid.
Liu, S., Li, E., Sun, Z., Fu, D., Duan, G., Jiang, M., . . . Zheng, P. (2019). Altered gut microbiota and short chain fatty acids in Chinese children with autism spectrum disorder. Scientific Reports,9(1). doi:10.1038/s41598-018-36430-z