期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：6
页码：1850-1855
DOI：10.1073/pnas.1422938112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceWe identified a form of surface motility in the bacterium Salmonella enterica serovar Typhimurium that is activated in low Mg2+ by PhoP/PhoQ, a regulatory system that hinders flagella expression and activity. PhoP furthers motility by promoting expression of the pagM gene, which specifies a small protein of unknown function, and also of two other genes that create the cytosolic conditions necessary for full pagM expression. Low Mg2+-promoted motility is a group behavior exclusive to a subset of S. enterica serovars harboring a particular allele of pagM. The pagM gene is present in nonfunctional allelic forms in certain S. enterica serovars and rarely found outside the genus Salmonella. Not required for virulence, PagM-mediated motility helps survival outside animal hosts. Flagella are multiprotein complexes necessary for swimming and swarming motility. In Salmonella enterica serovar Typhimurium, flagella-mediated motility is repressed by the PhoP/PhoQ regulatory system. We now report that Salmonella can move on 0.3% agarose media in a flagella-independent manner when experiencing the PhoP/PhoQ-inducing signal low Mg2+. This motility requires the PhoP-activated mgtA, mgtC, and pagM genes, which specify a Mg2+ transporter, an inhibitor of Salmonella's own F1Fo ATPase, and a small protein of unknown function, respectively. The MgtA and MgtC proteins are necessary for pagM expression because pagM mRNA levels were lower in mgtA and mgtC mutants than in wild-type Salmonella, and also because pagM expression from a heterologous promoter rescued motility in mgtA and mgtC mutants. PagM promotes group motility by a surface protein(s), as a pagM-expressing strain conferred motility upon a pagM null mutant, and proteinase K treatment eliminated motility. The pagM gene is rarely found outside subspecies I of S. enterica and often present in nonfunctional allelic forms in organisms lacking the identified motility. Deletion of the pagM gene reduced bacterial replication on 0.3% agarose low Mg2+ media but not in low Mg2+ liquid media. Our findings define a form of motility that allows Salmonella to scavenge nutrients and to escape toxic compounds in low Mg2+ semisolid environments.
