# Enrichment of Aquatic Xylan-Degrading Microbial Communities

## TL;DR

This study explores microbial communities from a lake in the Netherlands for their ability to break down xylan, a component of plant biomass, and finds that these communities can be enriched to enhance xylan degradation.

## Contribution

The study identifies novel xylan-degrading microbial communities and their potential for biotechnological applications beyond the commonly studied Bacteroidota.

## Key findings

- Enrichment with wheat arabinoxylan led to higher bacterial growth and complete xylan degradation compared to beechwood glucuronoxylan.
- Metagenomic analysis revealed significant shifts in microbial community composition during enrichment, with Gammaproteobacteria dominating early stages and Alphaproteobacteria in later stages.
- The enriched communities showed elevated levels of genes related to carbohydrate catabolism, particularly for arabinose, xylose, and xylan.

## Abstract

The transition towards a sustainable society involves the utilization of lignocellulosic biomass as a renewable feedstock for materials, fuel, and base chemicals. Lignocellulose consists of cellulose, hemicellulose, and lignin, forming a complex, recalcitrant matrix where efficient enzymatic saccharification is pivotal for accessing its valuable components. This study investigated microbial communities from brackish Lauwersmeer Lake, in The Netherlands, as a potential source of xylan-degrading enzymes. Environmental sediment samples were enriched with wheat arabinoxylan (WAX) and beechwood glucuronoxylan (BEX), with enrichment on WAX showing higher bacterial growth and complete xylan degradation compared to BEX. Metagenomic sequencing revealed communities consisting almost entirely of bacteria (>99%) and substantial shifts in composition during the enrichment. The first generation of seven-day enrichments on both xylans led to a high accumulation of Gammaproteobacteria (49% WAX, 84% BEX), which were largely replaced by Alphaproteobacteria (42% WAX, 69% BEX) in the fourth generation. Analysis of the protein function within the sequenced genomes showed elevated levels of genes associated with the carbohydrate catabolic process, specifically targeting arabinose, xylose, and xylan, indicating an adaptation to the primary monosaccharides present in the carbon source. The data open up the possibility of discovering novel xylan-degrading proteins from other sources aside from the thoroughly studied Bacteroidota.