A complex multilevel attack on Pseudomonas aeruginosa algT/U expression and algT/U activity results in the loss of alginate production.
A complex multilevel attack on Pseudomonas aeruginosa algT/U expression and algT/U activity results in the loss of alginate production.
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DOI：
10.1016/j.gene.2011.11.005
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发表时间：
2012-05-01
期刊：
影响因子：
3.5
通讯作者：
Mathee K
中科院分区：
文献类型：
--
作者：
Sautter R;Ramos D;Schneper L;Ciofu O;Wassermann T;Koh CL;Heydorn A;Hentzer M;Høiby N;Kharazmi A;Molin S;Devries CA;Ohman DE;Mathee K
机会致病菌铜绿假单胞菌感染是囊性纤维化（CF）患者发病和死亡的主要原因。这主要是由于细菌的基因型和表型变化导致CF肺中从典型的非粘液型转化为粘液型。类粘蛋白的转化表明一种叫做藻酸盐的胶囊状多糖的过度产生。在CF分离株中观察到的藻酸盐过度产生（Alg+）类粘蛋白表型是极其不稳定的。粘液变体的低氧张力生长容易选择非粘液变体。关闭机制已被映射到algT/U基因座，这种转换的分子基础部分归因于algT/U基因本身的突变。为了进一步表征导致不稳定表型的分子变化，使用了由于用mucA 22（PDO 300）替换mucA而组成型为Alg+的同基因PAO 1衍生物。mucA 22等位基因在粘液样CF分离株中很常见。34自发nonmucoid变种，或SAP（抑制藻酸盐生产）突变体，PDO 300的低氧张力下分离。约40%的sap突变体被携带algT/U的质粒拯救（A组）。其余的树液突变体则没有（B组）。组B的成员分为两个子集：一个与PAO 1相似，另一个与PDO 300相当。A组algT/U和mucA基因的序列分析显示mucA 22是完整的，而algT/U含有突变。一个B组sap突变体sap 22的遗传互补和测序显示，非粘液样表型是由于PA 3257中存在突变。PA 3257编码一种假定的周质蛋白酶。PA 3257突变导致algT/U表达降低。因此，algT/U的抑制是藻酸盐合成抑制的主要机制。
Infection by the opportunistic pathogen Pseudomonas aeruginosa is a leading cause of morbidity and mortality seen in cystic fibrosis (CF) patients. This is mainly due to the genotypic and phenotypic changes of the bacteria that cause conversion from a typical nonmucoid to a mucoid form in the CF lung. Mucoid conversion is indicative of overproduction of a capsule-like polysaccharide called alginate. The alginate-overproducing (Alg+) mucoid phenotype seen in the CF isolates is extremely unstable. Low oxygen tension growth of mucoid variants readily selects for nonmucoid variants. The switching off mechanism has been mapped to the algT/U locus, and the molecular basis for this conversion was partially attributed to mutations in the algT/U gene itself. To further characterize molecular changes resulting in the unstable phenotype, an isogenic PAO1 derivative that is constitutively Alg+ due to the replacement of the mucA with mucA22 (PDO300) was used. The mucA22 allele is common in mucoid CF isolates. Thirty-four spontaneous nonmucoid variants, or sap (suppressor of alginate production) mutants, of PDO300 were isolated under low oxygen tension. About forty percent of the sap mutants were rescued by a plasmid carrying algT/U (Group A). The remaining sap mutants were not (Group B). The members of Group B fall into two subsets: one similar to PAO1, and another comparable to PDO300. Sequence analysis of the algT/U and mucA genes in Group A shows that mucA22 is intact, whereas algT/U contains mutations. Genetic complementation and sequencing of one Group B sap mutant, sap22, revealed that the nonmucoid phenotype was due to the presence of a mutation in PA3257. PA3257 encodes a putative periplasmic protease. Mutation of PA3257 resulted in decreased algT/U expression. Thus, inhibition of algT/U is a primary mechanism for alginate synthesis suppression.