Skurnik M, Venho R, Toivanen P, al-Hendy A
Turku Centre for Biotechnology, University of Turku, Finland.
Mol Microbiol. 1995 Aug;17(3):575-94. doi: 10.1111/j.1365-2958.1995.mmi_17030575.x.
Yersinia enterocolitica serotype O:3 strain 6471/76-c (YeO3-c) was sensitive to bacteriophage phi R1-37 when grown at 37 degrees C but not when grown at 22 degrees C because of steric hindrance by abundant lipopolysaccharide (LPS) O-side chain (O-antigen) expressed at 22 degrees C. The transposon library of YeO3-c was grown at 37 degrees C and screened for phage phi R1-37-resistant transposon insertion mutants. Three types of mutant were isolated: (i) phage receptor mutants expressing O-antigen (LPS-smooth), (ii) phage receptor mutants not expressing O-antigen (LPS-rough), and (iii) LPS-smooth mutants with the phage receptor constitutively sterically blocked. Mutant type (i) was characterized in detail; the transposon insertion inactivates an operon, named the trs operon. The main findings based on this mutant are: (i) the frs operon is involved in the biosynthesis of the LPS outer core in YeO3-c; the nucleotide sequence of the trs operon revealed eight novel genes showing similarly to known polysaccharide biosynthetic genes of various Gram-negative bacteria as well as to capsule biosynthesis genes of Staphylococcus aureus; (ii) the biosynthesis of the core of YeO3-c involves at least two genetic loci; (iii) the trs operon is required for the biosynthesis of the bacteriophage phi R1-37 receptor structures; (iv) the homopolymeric O-antigen of YeO3-c is ligated to the inner core in Y. enterocolitica O:3; (v) the trs operon is located between the adk-hemH and galE-gsk gene pairs in the Y. enterocolitica chromosome; and (vi) the phage phi R1-37 receptor is present in many but not in all Y. enterocolitica serotypes. The results also allow us to speculate that the trs operon is a relic of the ancestral rfb region of Y. enterocolitica O:3 carrying genes indispensable for the completion of the core polysaccharide biosynthesis.
小肠结肠炎耶尔森菌O:3血清型菌株6471/76-c（YeO3-c）在37℃培养时对噬菌体phi R1-37敏感，但在22℃培养时不敏感，这是因为在22℃时表达的丰富脂多糖（LPS）O侧链（O抗原）产生了空间位阻。YeO3-c的转座子文库在37℃培养，并筛选对噬菌体phi R1-37有抗性的转座子插入突变体。分离出三种类型的突变体：（i）表达O抗原的噬菌体受体突变体（LPS光滑型），（ii）不表达O抗原的噬菌体受体突变体（LPS粗糙型），以及（iii）噬菌体受体被组成性空间阻断的LPS光滑型突变体。对突变体类型（i）进行了详细表征；转座子插入使一个名为trs操纵子的操纵子失活。基于该突变体的主要发现有：（i）trs操纵子参与YeO3-c中LPS外核心的生物合成；trs操纵子的核苷酸序列揭示了八个新基因，这些基因与各种革兰氏阴性菌的已知多糖生物合成基因以及金黄色葡萄球菌的荚膜生物合成基因相似；（ii）YeO3-c核心的生物合成涉及至少两个基因座；（iii）trs操纵子是噬菌体phi R1-37受体结构生物合成所必需的；（iv）YeO3-c的同聚O抗原在小肠结肠炎耶尔森菌O:3中连接到内核心；（v）trs操纵子位于小肠结肠炎耶尔森菌染色体中的adk-hemH和galE-gsk基因对之间；（vi）噬菌体phi R1-37受体存在于许多但并非所有小肠结肠炎耶尔森菌血清型中。这些结果还使我们推测，trs操纵子是小肠结肠炎耶尔森菌O:3祖先rfb区域的遗迹，携带完成核心多糖生物合成所必需的基因。
