Spirosoma linguale is a gram-negative, coiled bacterium belonging to the family Cytophagaceae. Its coiled morphology is unique in contrast to closely related bacteria belonging to the genus Spirosoma, which have a short, rod-shaped morphology. The mechanisms that generate unique cell morphology are still enigmatic. In this study, using the Spirosoma linguale ATCC33905 strain, we isolated β-lactam (cefoperazone and amoxicillin)-resistant clones. These clones showed two different cell morphological changes: relatively loosely curved cells or small, horseshoe-shaped cells. Whole-genome resequencing analysis revealed the genetic determinants of β-lactam resistance and changes in cell morphology. The loose-curved clones commonly had mutations in Slin_5958 genes encoding glutamyl-tRNA amidotransferase B subunit, whereas the small, horseshoe-shaped clones commonly had mutations in either Slin_5165 or Slin_5509 encoding pyruvate dehydrogenase (PDH) components. Two clones, CFP1ESL11 and CFL5ESL4, which carried only one mutation in Slin_5958, showed almost perfectly straight, rod-shaped cells in the presence of amoxicillin. This result suggests that penicillin-binding proteins targeted by amoxicillin play an important role in the formation of a coiled morphology in this bacterium. In contrast, supplementation with acetate did not rescue the growth defect and abnormal cell size of the CFP5ESL9 strain, which carried only one mutation in Slin_5509. These results suggest that PDH is involved in cell-size maintenance in this bacterium.

舌螺旋虫是一种革兰氏阴性卷曲细菌，属于噬菌科。与螺旋体属密切相关的细菌相比，其卷曲的形态是独特的，螺旋体属的细菌具有短棒状的形态。产生独特细胞形态的机制仍然是个谜。在本研究中，我们使用舌螺旋虫ATCC33905 菌株分离出 β-内酰胺（头孢哌酮和阿莫西林）抗性克隆。这些克隆显示出两种不同的细胞形态变化：相对松散弯曲的细胞或小的马蹄形细胞。全基因组重测序分析揭示了β-内酰胺耐药性的遗传决定因素和细胞形态的变化。松散弯曲的克隆通常在编码谷氨酰-tRNA酰胺转移酶 B 亚基的 Slin_5958 基因中发生突变，而小的马蹄形克隆通常在编码丙酮酸脱氢酶 (PDH) 成分的 Slin_5165 或 Slin_5509 中发生突变。两个克隆 CFP1ESL11 和 CFL5ESL4 在 Slin_5958 中仅携带一个突变，在阿莫西林存在下显示出几乎完全笔直的杆状细胞。这一结果表明阿莫西林靶向的青霉素结合蛋白在该细菌卷曲形态的形成中发挥重要作用。相比之下，补充醋酸盐并不能挽救 CFP5ESL9 菌株的生长缺陷和异常细胞大小，该菌株在 Slin_5509 中仅携带一个突变。这些结果表明 PDH 参与该细菌的细胞大小维持。