Condemine G, Castillo A, Passeri F, Enard C
Laboratoire de Génétique Moléculaire des Microorganismes et des Interactions Cellulaires, UMR-CNRS 5577, Villeurbanne, France.
Mol Plant Microbe Interact. 1999 Jan;12(1):45-52. doi: 10.1094/MPMI.1999.12.1.45.
Erwinia chrysanthemi 3937 synthesizes an exopolysaccharide (EPS) composed of rhamnose, galactose, and galacturonic acid. Fourteen transcriptional fusions in genes required for EPS synthesis, named eps, were obtained by Tn5-B21 mutagenesis. Eleven of them are clustered on the chromosome and are repressed by PecT, a regulator of pectate lyase synthesis. In addition, expression of these fusions is repressed by the catabolite regulatory protein, CRP, and induced in low osmolarity medium. The three other mutations are located in genes that are not regulated by pecT. A 13-kb DNA fragment containing pecT-regulated eps genes has been cloned. All the genes identified on this fragment are transcribed in the same orientation and could form a large operon. The promoter region of this operon has been sequenced. It contains a JUMP-start sequence, a sequence required for the expression of polysaccharide-associated operons. E. chrysanthemi 3937 produces a systemic soft rot on its host Saintpaulia ionantha. An eps mutant was less efficient than the wild-type strain in initiating a maceration symptom, suggesting that production of EPS is required for the full expression of the E. chrysanthemi virulence.
菊欧文氏菌3937合成一种由鼠李糖、半乳糖和半乳糖醛酸组成的胞外多糖（EPS）。通过Tn5 - B21诱变获得了14个与EPS合成所需基因（命名为eps）的转录融合体。其中11个聚集在染色体上，并受到果胶酸裂解酶合成调节因子PecT的抑制。此外，这些融合体的表达受到分解代谢调节蛋白CRP的抑制，并在低渗透压培养基中被诱导。另外三个突变位于不受pecT调节的基因中。一个包含受pecT调节的eps基因的13 kb DNA片段已被克隆。在该片段上鉴定出的所有基因都以相同方向转录，可能形成一个大操纵子。该操纵子的启动子区域已被测序。它包含一个JUMP - start序列，这是多糖相关操纵子表达所需的序列。菊欧文氏菌3937在其寄主非洲紫罗兰上引起系统性软腐病。一个eps突变体在引发浸解症状方面比野生型菌株效率低，这表明EPS的产生是菊欧文氏菌毒力充分表达所必需的。
