Stable, long-term interactions between fungi and algae or cyanobacteria, collectively known as lichens, have repeatedly evolved complex architectures with little resemblance to their component parts. Lacking any central scaffold, the shapes they assume are casts of secreted polymers that cement cells into place, determine the angle of phototropic exposure and regulate water relations. A growing body of evidence suggests that many lichen extracellular polymer matrices harbor unicellular, non-photosynthesizing organisms (UNPOs) not traditionally recognized as lichen symbionts. Understanding organismal input and uptake in this layer is key to interpreting the role UNPOs play in lichen biology. Here, we review both polysaccharide composition determined from whole, pulverized lichens and UNPOs reported from lichens to date. Most reported polysaccharides are thought to be structural cell wall components. The composition of the extracellular matrix is not definitively known. Several lines of evidence suggest some acidic polysaccharides have evaded detection in routine analysis of neutral sugars and may be involved in the extracellular matrix. UNPOs reported from lichens include diverse bacteria and yeasts for which secreted polysaccharides play important biological roles. We conclude by proposing testable hypotheses on the role that symbiont give-and-take in this layer could play in determining or modifying lichen symbiotic outcomes.

中文翻译：

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3D 生物膜：寻找将地衣共生体结合在一起的多糖。


真菌和藻类或蓝细菌（统称为地衣）之间稳定、长期的相互作用，反复进化出与其组成部分几乎没有相似之处的复杂结构。由于缺乏任何中心支架，它们呈现的形状是分泌聚合物的铸件，将细胞粘合到位，决定向光性曝光的角度并调节水关系。越来越多的证据表明，许多地衣细胞外聚合物基质含有单细胞非光合作用生物体（UNPO），传统上不被认为是地衣共生体。了解该层的有机输入和吸收是解释 UNPO 在地衣生物学中所发挥作用的关键。在这里，我们回顾了从完整的、粉碎的地衣中测定的多糖成分以及迄今为止从地衣中报告的 UNPO。大多数报道的多糖被认为是结构细胞壁成分。细胞外基质的组成尚不清楚。一些证据表明，一些酸性多糖在中性糖的常规分析中逃避了检测，并且可能参与细胞外基质。据报道，地衣中的 UNPO 包括多种细菌和酵母，其分泌的多糖发挥着重要的生物学作用。最后，我们提出了关于该层中的共生体给予和接受在确定或改变地衣共生结果中所发挥的作用的可检验的假设。