An exopolysaccharide pathway from a freshwater Sphingomonas isolate.

IF 2.7 3区 生物学 Q3 MICROBIOLOGY Journal of Bacteriology Pub Date : 2024-08-22 Epub Date: 2024-07-15 DOI:10.1128/jb.00169-24
Alexandra G Goetsch, Daniel Ufearo, Griffin Keiser, Christian Heiss, Parastoo Azadi, David M Hershey
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Abstract

Bacteria embellish their cell envelopes with a variety of specialized polysaccharides. Biosynthesis pathways for these glycans are complex, and final products vary greatly in their chemical structures, physical properties, and biological activities. This tremendous diversity comes from the ability to arrange complex pools of monosaccharide building blocks into polymers with many possible linkage configurations. Due to the complex chemistry of bacterial glycans, very few biosynthetic pathways have been defined in detail. As part of an initiative to characterize novel polysaccharide biosynthesis enzymes, we isolated a bacterium from Lake Michigan called Sphingomonas sp. LM7 that is proficient in exopolysaccharide (EPS) production. We identified genes that contribute to EPS biosynthesis in LM7 by screening a transposon mutant library for colonies displaying altered colony morphology. A gene cluster was identified that appears to encode a complete wzy/wzx-dependent polysaccharide assembly pathway. Deleting individual genes in this cluster caused a non-mucoid phenotype and a corresponding loss of EPS secretion, confirming the role of this gene cluster in polysaccharide production. We extracted EPS from LM7 cultures and determined that it contains a linear chain of 3- and 4-linked glucose, galactose, and glucuronic acid residues. Finally, we show that the EPS pathway in Sphingomonas sp. LM7 diverges from that of sphingan-family EPSs and adhesive polysaccharides such as the holdfast that are present in other Alphaproteobacteria. Our approach of characterizing complete biosynthetic pathways holds promise for engineering polysaccharides with valuable properties.

Importance: Bacteria produce complex polysaccharides that serve a range of biological functions. These polymers often have properties that make them attractive for industrial applications, but they remain woefully underutilized. In this work, we studied a novel polysaccharide called promonan that is produced by Sphingomonas sp. LM7, a bacterium we isolated from Lake Michigan. We extracted promonan from LM7 cultures and identified which sugars are present in the polymer. We also identified the genes responsible for polysaccharide production. Comparing the promonan genes to those of other bacteria showed that promonan is distinct from previously characterized polysaccharides. We conclude by discussing how the promonan pathway could be used to produce new polysaccharides through genetic engineering.

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淡水鞘氨醇单胞菌的外多糖途径。
细菌用各种特殊的多糖来装饰它们的细胞包膜。这些聚糖的生物合成途径非常复杂,最终产品的化学结构、物理性质和生物活性也千差万别。这种巨大的多样性来自于将复杂的单糖结构单元排列成具有多种可能连接构型的聚合物的能力。由于细菌聚糖的化学结构复杂,很少有生物合成途径被详细定义。作为鉴定新型多糖生物合成酶的计划的一部分,我们从密歇根湖中分离出了一种叫做鞘氨醇单胞菌 LM7 的细菌,它能熟练地生产外多糖(EPS)。我们通过筛选转座子突变体文库中显示菌落形态改变的菌落,确定了有助于 LM7 中 EPS 生物合成的基因。我们发现了一个基因簇,它似乎编码了一个完整的依赖于 wzy/wzx 的多糖组装途径。删除该基因簇中的单个基因会导致无黏液表型和相应的 EPS 分泌损失,从而证实了该基因簇在多糖生产中的作用。我们从 LM7 培养物中提取了 EPS,并确定它含有由 3-和 4-连接的葡萄糖、半乳糖和葡萄糖醛酸残基组成的线性链。最后,我们发现鞘氨醇单胞菌 LM7 的 EPS 通路与鞘氨醇类 EPS 和粘附性多糖(如固着多糖)的通路不同,后者存在于其他变形蛋白细菌中。我们对完整的生物合成途径进行表征的方法有望为工程设计具有重要特性的多糖带来希望:细菌产生复杂的多糖,具有多种生物功能。这些聚合物通常具有吸引工业应用的特性,但其利用率仍然很低。在这项工作中,我们研究了从密歇根湖中分离出来的鞘氨醇单胞菌 LM7 产生的一种名为 Promonan 的新型多糖。我们从 LM7 培养物中提取了丙糖,并确定了聚合物中含有哪些糖。我们还确定了负责生产多糖的基因。将原聚糖基因与其他细菌的基因进行比较后发现,原聚糖与以前的多糖不同。最后,我们讨论了如何通过基因工程利用原聚糖途径生产新的多糖。
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来源期刊
Journal of Bacteriology
Journal of Bacteriology 生物-微生物学
CiteScore
6.10
自引率
9.40%
发文量
324
审稿时长
1.3 months
期刊介绍: The Journal of Bacteriology (JB) publishes research articles that probe fundamental processes in bacteria, archaea and their viruses, and the molecular mechanisms by which they interact with each other and with their hosts and their environments.
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