The human gut microbiome has recently been a hot topic in nutrition science. It is a complex system containing different gut bacteria which interact with the gastrointestinal tract and provide health benefits to the host. In order to reap the benefits of beneficial gut bacteria, they need to be fed with certain non-digestible polysaccharides (NPDs) that gut bacteria will ferment. These gut bacteria then use fermentation end products of NPDs degradation to cross-feed each other to grow.

Aside from cross-feeding, many of these fermentation end products are absorbed by the host for different metabolic processes.  Some of these fermentation end products are short-chain fatty acids, known to confer health benefits in various ways, for example, lowering the level of inflammation, strengthening gut-barrier function, regulating satiety hormones, and regulating blood sugar levels (1-3)

However, there are also other end products released after the fermentation of NPDs. One of these was identified in a recent study on complex arabinoxylan: ferulic acid (4).

How do gut bacteria break down arabinoxylan molecules?

A recent study assessed whether and how certain gut bacteria, Bacteroidetes,  can degrade complex arabinoxylan molecules. This is a kind of NPD with a complex structure found in the starchy endosperm of the wheat kernel, the most nutritious part of the wheat.

The aim of the study was to understand how exactly these gut bacteria break down arabinoxylan. Previous research has already shown that there are specific gene clusters, called PULs (polysaccharide-utilization loci) encoding for the degradation of simple arabinoxylan. However, the breakdown of complex arabinoxylan was still poorly understood. These gene clusters (PULs) are found in Bacteroidetes. 

In order to gain further insights into this process,  PULs encode for enzymes needed to break down the complex arabinoxylan (esterases) for the degradation of complex arabinoxylan (also called esterase enriched genes (EGE)) were identified. 

Moreover, this article revealed that several Bacteroides species (like B. intestinalis and B. cellulosilyticus) can identify the difference in complexity of arabinoxylan and deploy different PULs to efficiently metabolize them. This metabolization of complex arabinoxylan results in the accumulation of ferulic acid, a compound that is mainly absorbed in the colon, where it is released by microbial esterases (see figure 1). 

Ferulic acid is a phenolic phytochemical known to have antioxidative, immunomodulatory and anti-inflammatory properties, and can thus be very beneficial for our health. In fact, apart from the increased production of short-chain fatty acid, the accumulation of ferulic acid during the metabolism of arabinoxylan by the colonic Bacteroidetes species, is the icing on the cake and could potentially provide further insights into the molecular basis for the observed impact of arabinoxylan on human health and specifically its immunovigilance activity. 

In summary, the work conducted shows that complex arabinoxylan molecules are degraded by several Bacteroidetes species by the use of the EGE PUL (4). Additionally, this degradation leads to the accumulation of ferulic acid, which is a phenolic phytochemical that exerts antioxidative, immunomodulatory and anti-inflammatory properties (5). Yet another indication that the use of Bacteroidetes as a probiotic in combination with complex arabinoxylans as an accompanying prebiotic may provide great opportunities to target immune health

REFERENCES

1. Tilg H, Moschen AR. Microbiota and diabetes: an evolving relationship. Gut. 2014;63(9):1513-21.

2. Säemann MD, Böhmig GA, Osterreicher CH, Burtscher H, Parolini O, Diakos C, et al. Anti-inflammatory effects of sodium butyrate on human monocytes: potent inhibition of IL-12 and up-regulation of IL-10 production. Faseb j. 2000;14(15):2380-2.

3. Kimura I. [Host energy regulation via SCFAs receptors, as dietary nutrition sensors, by gut microbiota]. Yakugaku Zasshi. 2014;134(10):1037-42.

4. Pereira GV, Abdel-Hamid AM, Dutta S, D’Alessandro-Gabazza CN, Wefers D, Farris JA, et al. Degradation of complex arabinoxylans by human colonic Bacteroidetes. Nature Communications. 2021;12(1):459.

5. Srinivasan M, Sudheer AR, Menon VP. Ferulic Acid: therapeutic potential through its antioxidant property. J Clin Biochem Nutr. 2007;40(2):92-100.


At Bioactor we developed Naxus®, a next-generation prebiotic extract from the wheat endosperm. Naxus® is known for its strong bifidogenic activity and clinically proven to enhance immunity, gut health and improve glucose control.