Data_Sheet_1_Biogels in Soils: Plant Mucilage as a Biofilm Matrix That Shapes the Rhizosphere Microbial Habitat.docx

Mucilage is a gelatinous high-molecular-weight substance produced by almost all plants, serving numerous functions for plant and soil. To date, research has mainly focused on hydraulic and physical functions of mucilage in the rhizosphere. Studies on the relevance of mucilage as a microbial habitat are scarce. Extracellular polymeric substances (EPS) are similarly gelatinous high-molecular-weight substances produced by microorganisms. EPS support the establishment of microbial assemblages in soils, mainly through providing a moist environment, a protective barrier, and serving as carbon and nutrient sources. We propose that mucilage shares physical and chemical properties with EPS, functioning similarly as a biofilm matrix covering a large extent of the rhizosphere. Our analyses found no evidence of consistent differences in viscosity and surface tension between EPS and mucilage, these being important physical properties. With regard to chemical composition, polysaccharide, protein, neutral monosaccharide, and uronic acid composition also showed no consistent differences between these biogels. Our analyses and literature review suggest that all major functions known for EPS and required for biofilm formation are also provided by mucilage, offering a protected habitat optimized for nutrient mobilization. Mucilage enables high rhizo-microbial abundance and activity by functioning as carbon and nutrient source. We suggest that the role of mucilage as a biofilm matrix has been underestimated, and should be considered in conceptual models of the rhizosphere.

黏液（Mucilage）是几乎所有植物均可产生的胶状高分子量物质，可为植物与土壤发挥多种功能。迄今为止，相关研究多聚焦于根际（rhizosphere）中黏液的水力与物理功能，而针对黏液作为微生物栖息生境的相关研究则较为匮乏。胞外聚合物（Extracellular Polymeric Substances, EPS）是微生物产生的另一类胶状高分子量物质，其主要通过提供湿润微环境、保护性屏障以及作为碳源与营养源，助力土壤中微生物群落的定植。本研究提出，黏液与EPS具备相似的物理与化学性质，可类似生物膜（Biofilm）基质一般覆盖根际的大面积区域。我们的分析显示，EPS与黏液在黏度与表面张力这两项关键物理性质上，并无一致的显著差异。就化学组成而言，两类生物凝胶（Biogels）在多糖、蛋白质、中性单糖及糖醛酸的组成上，同样未表现出一致的显著差异。我们的分析与文献综述表明，黏液同样具备EPS已知的、生物膜形成所需的全部核心功能，可为营养动员提供优化的保护型栖息生境。黏液可通过充当碳源与营养源，提升根际微生物的丰度与活性。我们认为，黏液作为生物膜基质的作用此前被低估，未来根际概念模型中应纳入该要素。