Weimer R M, Creighton C x, Stassinopoulos A, Youderian P, Hartzell P L
Department of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, Idaho 83844-3052, USA.
J Bacteriol. 1998 Oct;180(20):5357-68. doi: 10.1128/JB.180.20.5357-5368.1998.
Three independent Tn5-lac insertions in the S1 locus of Myxococcus xanthus inactivate the sglK gene, which is nonessential for growth but required for social motility and multicellular development. The sequence of sglK reveals that it encodes a homologue of the chaperone HSP70 (DnaK). The sglK gene is cotranscribed with the upstream grpS gene, which encodes a GrpE homologue. Unlike sglK, grpS is not required for social motility or development. Wild-type M. xanthus is encased in extracellular polysaccharide filaments associated with the multimeric fibrillin protein. Mutations in sglK inhibit cell cohesion, the binding of Congo red, and the synthesis or secretion of fibrillin, indicating that sglK mutants do not make fibrils. The fibR gene, located immediately upstream of the grpS-sglK operon, encodes a product which is predicted to have a sequence similar to those of the repressors of alginate biosynthesis in Pseudomonas aeruginosa and Pseudomonas putida. Inactivation of fibR leads to the overproduction of fibrillin, suggesting that M. xanthus fibril production and Pseudomonas alginate production are regulated in analogous ways. M. xanthus and Pseudomonas exopolysaccharides may play similar roles in a mechanism of social motility conserved in these gram-negative bacteria.
在黄色粘球菌S1位点的三个独立Tn5-lac插入使sglK基因失活，该基因对生长不是必需的，但对群体运动和多细胞发育是必需的。sglK的序列显示它编码伴侣蛋白HSP70（DnaK）的同源物。sglK基因与上游的grpS基因共转录，grpS基因编码GrpE同源物。与sglK不同，grpS对群体运动或发育不是必需的。野生型黄色粘球菌被包裹在与多聚体纤维蛋白相关的细胞外多糖丝中。sglK中的突变抑制细胞黏附、刚果红结合以及纤维蛋白的合成或分泌，表明sglK突变体不形成纤维。位于grpS-sglK操纵子上游紧邻的fibR基因编码一种产物，预测其序列与铜绿假单胞菌和恶臭假单胞菌中藻酸盐生物合成阻遏物的序列相似。fibR的失活导致纤维蛋白的过量产生，表明黄色粘球菌纤维产生和假单胞菌藻酸盐产生以类似方式受到调控。黄色粘球菌和假单胞菌的胞外多糖可能在这些革兰氏阴性细菌中保守的群体运动机制中发挥相似作用。
