The salCAB operon of Azospirillum irakense, required for growth on salicin, is repressed by SalR, a transcriptional regulator that belongs to the Lacl/GalR family.
The salAB genes of Azospirillum irakense KBC1, which encode two aryl-beta-glucosidases, are required for growth on salicin. In the 4-kb region upstream of the salAB genes, two additional genes, salC and salR, were identified. SalC shows characteristics of the outer membrane receptors in the FepA/FhuA family. The salC AB genes are transcribed as a polycistronic mRNA. The salR gene encodes a protein homologous to the LacI/GalR family of transcriptional repressors. Expression of the sal operon, measured by means of a salC-gusA translational fusion in A. irkense KBC1, requires the presence of aryl-beta-glucosides such as arbutin and salicin. Expression is markedly enhanced when a simple carbon source, like glucose, cellobiose or malate, is added to the medium. In a salR mutant, expression of the salC-gusA fusion does not require an aryl-beta-glucoside inducer. Expression of a salR-gusA fusion is constitutive. The product of arbutin hydrolysis (hydroquinone) partly inhibits the expression of a salC-gusA fusion in arbutin- or salicin-containing minimal medium. This effect is independent of SalR. Salicylalcohol, the hydrolysis product of salicin, also partly inhibits salC expression in a SalR-independent fashion, but only in salicin-containing minimal medium.
Somers
E
E
F.A. Janssens Laboratory of Genetics, Katholieke Universiteit Leuven, Heverlee, Belgium.
Keijers
V
V
Ptacek
D
D
Halvorsen Ottoy
M
M
Srinivasan
M
M
Vanderleyden
J
J
Faure
D
D
D000595:Amino Acid Sequence; D001104:Arbutin / Q000378:metabolism; D016949:Azospirillum / Q000235:genetics*; D001426:Bacterial Proteins; D001592:Benzyl Alcohols / Q000378:metabolism* / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D004790:Enzyme Induction; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005960:Glucosides / Q000494:pharmacology; D006868:Hydrolysis; D006873:Hydroquinones / Q000494:pharmacology; D008969:Molecular Sequence Data; D009876:Operon; D011956:Receptors, Cell Surface / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D001617:beta-Glucosidase / Q000235:genetics*
D001426:Bacterial Proteins; D001592:Benzyl Alcohols; D002352:Carrier Proteins; D005960:Glucosides; D006873:Hydroquinones; D011956:Receptors, Cell Surface; D012097:Repressor Proteins; C412711:SalC protein, Azospirillum; C412713:SalR protein, Azospirillum irakense; C005696:salicin; D001104:Arbutin; D001617:beta-Glucosidase; C010631:salicyl alcohol; C031927:hydroquinone