title: Phenotypes and gene expression profiles of Saccharopolyspora erythraea rifampicin-resistant (rif) mutants affected in erythromycin production.
abstract: BACKGROUND
  There is evidence from previous works that bacterial secondary metabolism may be stimulated by genetic manipulation of RNA polymerase (RNAP). In this study we have used rifampicin selection as a strategy to genetically improve the erythromycin producer Saccharopolyspora erythraea.
  
  
  RESULTS
  Spontaneous rifampicin-resistant (rif) mutants were isolated from the parental strain NRRL2338 and two rif mutations mapping within rpoB, S444F and Q426R, were characterized. With respect to the parental strain, S444F mutants exhibited higher respiratory performance and up to four-fold higher final erythromycin yields; in contrast, Q426R mutants were slow-growing, developmental-defective and severely impaired in erythromycin production. DNA microarray analysis demonstrated that these rif mutations deeply changed the transcriptional profile of S. erythraea. The expression of genes coding for key enzymes of carbon (and energy) and nitrogen central metabolism was dramatically altered in turn affecting the flux of metabolites through erythromycin feeder pathways. In particular, the valine catabolic pathway that supplies propionyl-CoA for biosynthesis of the erythromycin precursor 6-deoxyerythronolide B was strongly up-regulated in the S444F mutants, while the expression of the biosynthetic gene cluster of erythromycin (ery) was not significantly affected. In contrast, the ery cluster was down-regulated (<2-fold) in the Q426R mutants. These strains also exhibited an impressive stimulation of the nitrogen regulon, which may contribute to lower erythromycin yields as erythromycin production was strongly inhibited by ammonium.
  
  
  CONCLUSIONS
  Rifampicin selection is a simple and reliable tool to investigate novel links between primary and secondary metabolism and morphological differentiation in S. erythraea and to improve erythromycin production. At the same time genome-wide analysis of expression profiles using DNA microarrays allowed information to be gained about the mechanisms underlying the stimulatory/inhibitory effects of the rif mutations on erythromycin production.
authors.affiliation: Department of Biological and Environmental Sciences and Technologies, University of Salento, 73100 Lecce, Italy. alifano@ilenic.unile.it.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Carata
authors.forename: Clelia
authors.initials: C
authors.lastname: Peano
authors.forename: Salvatore M
authors.initials: SM
authors.lastname: Tredici
authors.forename: Francesco
authors.initials: F
authors.lastname: Ferrari
authors.forename: Adelfia
authors.initials: A
authors.lastname: Talà
authors.forename: Giorgio
authors.initials: G
authors.lastname: Corti
authors.forename: Silvio
authors.initials: S
authors.lastname: Bicciato
authors.forename: Gianluca
authors.initials: G
authors.lastname: De Bellis
authors.forename: Pietro
authors.initials: P
authors.lastname: Alifano