title: Proteomic profiling of L-cysteine induced selenite resistance in Enterobacter sp. YSU.
abstract: BACKGROUND
  Enterobacter sp. YSU is resistant to several different heavy metal salts, including selenite. A previous study using M-9 minimal medium showed that when the selenite concentration was 100,000 times higher than the sulfate concentration, selenite entered Escherichia coli cells using two pathways: a specific and a non-specific pathway. In the specific pathway, selenite entered the cells through a yet to be characterized channel dedicated for selenite. In the non-specific pathway, selenite entered the cells through a sulfate permease channel. Addition of L-cystine, an L-cysteine dimer, appeared to indirectly decrease selenite import into the cell through the non-specific pathway. However, it did not affect the level of selenite transport into the cell through the specific pathway.
  
  
  RESULTS
  Growth curves using M-9 minimal medium containing 40 mM selenite and 1 mM sulfate showed that Enterobacter sp. YSU grew when L-cysteine was present but died when it was absent. Differential protein expression analysis by two dimensional gel electrophoresis showed that CysK was present in cultures containing selenite and lacking L-cysteine but absent in cultures containing both selenite and L-cysteine. Additional RT-PCR studies demonstrated that transcripts for the sulfate permease genes, cysA, cysT and cysW, were down-regulated in the presence of L-cysteine.
  
  
  CONCLUSIONS
  L-cysteine appeared to confer selenite resistance upon Enterobacter sp. YSU by decreasing the level of selenite transport into the cell through the non-specific pathway.
authors.affiliation: Department of Biological Sciences, Youngstown State University, OH 44555, USA. a_jasenec@hotmail.com
authors.forename: Ashley
authors.initials: A
authors.lastname: Jasenec
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Barasa
authors.forename: Samatha
authors.initials: S
authors.lastname: Kulkarni
authors.forename: Nabeel
authors.initials: N
authors.lastname: Shaik
authors.forename: Swarnalatha
authors.initials: S
authors.lastname: Moparthi
authors.forename: Venkataramana
authors.initials: V
authors.lastname: Konda
authors.forename: Jonathan
authors.initials: J
authors.lastname: Caguiat