Nonulosonic acids (NulOs) are a diverse family of 9-carbon α-keto acid sugars that are involved in a wide range of functions across all branches of life. The family of NulOs includes the sialic acids as well as the prokaryote-specific NulOs. Select bacteria biosynthesize the sialic acid N-acetylneuraminic acid (Neu5Ac), and the ability to produce this sugar and its subsequent incorporation into cell-surface structures is implicated in a variety of bacteria–host interactions. Furthermore, scavenging of sialic acid from the environment for energy has been characterized across a diverse group of bacteria, mainly human commensals and pathogens. In addition to sialic acid, bacteria have the ability to biosynthesize prokaryote-specific NulOs, of which there are several known isomers characterized. These prokaryotic NulOs are similar in structure to Neu5Ac but little is known regarding their role in bacterial physiology. Here, we discuss the diversity in structure, the biosynthesis pathways, and the functions of bacteria-specific NulOs. These carbohydrates are phylogenetically widespread among bacteria, with numerous structurally unique modifications recognized. Despite the diversity in structure, the NulOs are involved in similar functions such as motility, biofilm formation, host colonization, and immune evasion.

Nonulosonic 酸 (NulOs) 是一个多样化的 9 碳 α-酮酸糖家族，涉及生命各个分支的广泛功能。NulOs 家族包括唾液酸以及原核生物特异性 NulOs。选择细菌生物合成唾液酸N-乙酰神经氨酸（Neu5Ac），以及产生这种糖的能力及其随后掺入细胞表面结构的能力与多种细菌-宿主相互作用有关。此外，从环境中清除唾液酸以获取能量的特征已在多种细菌中进行表征，主要是人类共生体和病原体。除唾液酸外，细菌还具有生物合成原核生物特异性 NulO 的能力，其中有几种已知的异构体。这些原核生物 NulO 在结构上与 Neu5Ac 相似，但对其在细菌生理学中的作用知之甚少。在这里，我们讨论了细菌特异性 NulOs 的结构多样性、生物合成途径和功能。这些碳水化合物在细菌中广泛分布，具有公认的许多结构上独特的修饰。尽管结构上存在差异，但 NulOs 参与了类似的功能，例如运动、生物膜形成、宿主定植和免疫逃避。