PUL-Mediated Plant Cell Wall Polysaccharide Utilization in the Gut Bacteroidetes.

Zhenzhen Hao,Xiaolu Wang,Xiaoyun Su,Jie Zhang,Huoqing Huang,Tao Tu,Haomeng Yang,Huiying Luo

doi:10.3390/ijms22063077

Abstract

Plant cell wall polysaccharides (PCWP) are abundantly present in the food of humans and feed of livestock. Mammalians by themselves cannot degrade PCWP but rather depend on microbes resident in the gut intestine for deconstruction. The dominant Bacteroidetes in the gut microbial community are such bacteria with PCWP-degrading ability. The polysaccharide utilization systems (PUL) responsible for PCWP degradation and utilization are a prominent feature of Bacteroidetes. In recent years, there have been tremendous efforts in elucidating how PULs assist Bacteroidetes to assimilate carbon and acquire energy from PCWP. Here, we will review the PUL-mediated plant cell wall polysaccharides utilization in the gut Bacteroidetes focusing on cellulose, xylan, mannan, and pectin utilization and discuss how the mechanisms can be exploited to modulate the gut microbiota.

Highlights

Plant cell wall polysaccharides (PCWP), mainly consisting of cellulose, hemicellulose, and pectin, are among the most abundant renewable carbohydrates in nature [1,2]
PCWP degradation requires orchestrated action of a multitude of carbohydrate-active enzymes (CAZymes), of those classified as glycoside hydrolase (GH), carbohydrate esterase (CE), polysaccharide lyase (PL), and recently discovered polysaccharide monooxygenase (PMO) [13,14]
Synergy of these enzymes is exemplified by three strategies which are (i) free enzymes, typified by the aerobic filamentous fungus Trichoderma reesei [15]; (ii) cellulosome, best known in the anaerobic bacterium Clostridium thermocellum [16]; and (iii) an intermediate form represented by a multi-modular bifunctional enzyme CelA found in the Caldicellulosiruptor bescii [17,18,19]

Summary

Introduction

Plant cell wall polysaccharides (PCWP), mainly consisting of cellulose, hemicellulose, and pectin, are among the most abundant renewable carbohydrates in nature [1,2]. The Bacteroidetes constitute a dominant phylum in the intestinal tract of humans and livestock animals and these bacteria metabolize a broad scope of dietary and host-derived polysaccharides, including the relatively simple glycans (such as starch [23], levan [24], and inulin) as well as cellulose and complex hemicellulose polysaccharides (like xylan [25,26,27], arabinan [28], galactan [29], arabinogalactan [30], xyloglucan [31,32], and galactomannans [33]) Their genomes typically contain abundant GHs and PLs corresponding to the varying types of polysaccharides [22,34]. We will review the PUL systems of the dominant Bacteroidetes in the gut, focusing on PUL-mediated utilization of major components of the plant-derived polysaccharides by the bacteria

The Bacteroidetes in the Gut

Conclusions