Yu H, Schurr M J, Deretic V
Department of Microbiology, University of Texas Health Science Center at San Antonio 78284-7758, USA.
J Bacteriol. 1995 Jun;177(11):3259-68. doi: 10.1128/jb.177.11.3259-3268.1995.
Mucoid colony morphology is the result of the overproduction of the exopolysaccharide alginate and is considered to be a major pathogenic determinant expressed by Pseudomonas aeruginosa during chronic respiratory infections in cystic fibrosis. Conversion to mucoidy can be caused by mutations in the second or third gene of the stress-responsive system algU mucA mucB. AlgU is 66% identical to the alternative sigma factor RpoE (sigma E) from Escherichia coli and Salmonella typhimurium and directs transcription of several critical alginate biosynthetic and regulatory genes. AlgU is also required for the full resistance of P. aeruginosa to reactive oxygen intermediates and heat killing. In this work, we report that E. coli sigma E can complement phenotypic defects of algU inactivation in P. aeruginosa: (i) the rpoE gene from E. coli complemented an algU null mutant of P. aeruginosa to mucoidy; (ii) the presence of the E. coli rpoE gene in P. aeruginosa induced alginate production in the standard genetic nonmucoid strain PAO1; (iii) the plasmid-borne E. coli rpoE gene induced transcription of algD, a critical algU-dependent alginate biosynthetic gene; and (iv) when present in algU::Tcr mutants, E. coli rpoE partially restored resistance to paraquat, a redox cycling compound that increases intracellular levels of superoxide radicals. A new gene, mclA, encoding a polypeptide with an apparent molecular mass of 27.7 kDa was identified immediately downstream of rpoE in E. coli. The predicted product of this gene is 28% identical (72% similar) to MucA, a negative regulator of AlgU activity in P. aeruginosa. The results reported in this study demonstrate that RpoE and AlgU are functionally interchangeable in P. aeruginosa and suggest that elements showing sequence similarity to those known to regulate AlgU activity in P. aeruginosa are also present in other bacteria.
黏液样菌落形态是胞外多糖藻酸盐过度产生的结果，被认为是铜绿假单胞菌在囊性纤维化慢性呼吸道感染期间表达的主要致病决定因素。向黏液样转变可能由应激反应系统algU mucA mucB的第二个或第三个基因的突变引起。AlgU与来自大肠杆菌和鼠伤寒沙门氏菌的替代西格玛因子RpoE（西格玛E）有66%的同一性，并指导几个关键的藻酸盐生物合成和调节基因的转录。AlgU对于铜绿假单胞菌对活性氧中间体和热杀伤的完全抗性也是必需的。在这项工作中，我们报告大肠杆菌西格玛E可以弥补铜绿假单胞菌中algU失活的表型缺陷：（i）来自大肠杆菌的rpoE基因将铜绿假单胞菌的algU缺失突变体互补为黏液样；（ii）铜绿假单胞菌中大肠杆菌rpoE基因的存在诱导了标准遗传非黏液样菌株PAO1中藻酸盐的产生；（iii）质粒携带的大肠杆菌rpoE基因诱导了algD的转录，algD是一个关键的依赖AlgU的藻酸盐生物合成基因；（iv）当存在于algU::Tcr突变体中时，大肠杆菌rpoE部分恢复了对百草枯的抗性，百草枯是一种氧化还原循环化合物，可增加细胞内超氧自由基的水平。在大肠杆菌中，紧挨着rpoE下游鉴定出一个新基因mclA，它编码一种表观分子量为27.7 kDa的多肽。该基因的预测产物与MucA有28%的同一性（72%的相似性），MucA是铜绿假单胞菌中AlgU活性的负调节因子。本研究报告的结果表明，RpoE和AlgU在铜绿假单胞菌中功能上是可互换的，并表明在其他细菌中也存在与已知调节铜绿假单胞菌中AlgU活性的元件具有序列相似性的元件。
