title: Evolution of a multi-step phosphorelay signal transduction system in Ensifer: recruitment of the sigma factor RpoN and a novel enhancer-binding protein triggers acid-activated gene expression.
abstract: Most Ensifer strains are comparatively acid sensitive, compromising their persistence in low pH soils. In the acid-tolerant strain Ensifer medicae WSM419, the acid-activated expression of lpiA is essential for enhancing survival in lethal acidic conditions. Here we characterise a multi-step phosphorelay signal transduction pathway consisting of TcsA, TcrA, FsrR, RpoN and its cognate enhancer-binding protein EbpA, which is required for the induction of lpiA and the downstream acvB gene. The fsrR, tcrA, tcsA and rpoN genes were constitutively expressed, whereas lpiA and acvB were strongly acid-induced. RACE mapping revealed that lpiA/acvB were co-transcribed as an operon from an RpoN promoter. In most Ensifer species, lpiA/acvB is located on the chromosome and the sequence upstream of lpiA lacks an RpoN-binding site. Nearly all Ensifer meliloti strains completely lack ebpA, tcrA, tcsA and fsrR regulatory loci. In contrast, E. medicae strains have lpiA/acvB and ebpA/tcrA/tcsA/fsrR co-located on the pSymA megaplasmid, with lpiA/acvB expression coupled to an RpoN promoter. Here we provide a model for the expression of lpiA/acvB in E. medicae. This unique acid-activated regulatory system provides insights into an evolutionary process which may assist the adaptation of E. medicae to acidic environmental niches.
authors.affiliation: School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, 6150, Australia.
authors.forename: Rui
authors.initials: R
authors.lastname: Tian
authors.affiliation: School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, 6150, Australia.
authors.forename: Stephan
authors.initials: S
authors.lastname: Heiden
authors.affiliation: School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, 6150, Australia.
authors.forename: Wan A M
authors.initials: WA
authors.lastname: Osman
authors.affiliation: School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, 6150, Australia.
authors.forename: Julie K
authors.initials: JK
authors.lastname: Ardley
authors.affiliation: The James Hutton Institute, Invergowrie, Dundee, DD2 5DA, UK.
authors.forename: Euan K
authors.identifier: 0000-0001-7969-6570
authors.initials: EK
authors.lastname: James
authors.affiliation: Curtin University Sustainability Policy Institute, Curtin University, Bentley, WA, Australia.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Gollagher
authors.affiliation: School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, 6150, Australia.
authors.forename: Ravi
authors.initials: R
authors.lastname: Tiwari
authors.affiliation: DOE Joint Genome Institute, Walnut Creek, CA, USA.
authors.forename: Rekha
authors.initials: R
authors.lastname: Seshadri
authors.affiliation: DOE Joint Genome Institute, Walnut Creek, CA, USA.
authors.forename: Nikos C
authors.initials: NC
authors.lastname: Kyrpides
authors.affiliation: School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, 6150, Australia.
authors.forename: Wayne G
authors.identifier: 0000-0002-3780-8965
authors.initials: WG
authors.lastname: Reeve
mesh_terms: D000143:Acids; D000818:Animals; D001665:Binding Sites; D004269:DNA, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D009586:Nitrogen Fixation; D011401:Promoter Regions, Genetic; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D020579:Sinorhizobium / Q000235:genetics* / Q000378:metabolism*
chemical_list: D000143:Acids; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D012808:Sigma Factor