Acetate Permease (ActP) Is Responsible for Tellurite (TeO ₃ ²⁻ ) Uptake and Resistance in Cells of the Facultative Phototroph Rhodobacter capsulatus

Abstract

The highly toxic oxyanion tellurite has to enter the cytoplasm of microbial cells in order to fully express its toxicity. Here we show that in the phototroph Rhodobacter capsulatus, tellurite exploits acetate permease (ActP) to get into the cytoplasm and that the levels of resistance and uptake are linked.

On the role of a specific insert in acetate permeases (ActP) for tellurite uptake in bacteria: Functional and structural studies

“…Despite the important role of this uptake activity, very few studies have addressed this issue. In R. capsulatus it has been shown that a mutant impaired in tellurite uptake became highly resistant to the oxyanion and the uptake defect was restored by the acetate permease actP2 gene [17], supporting an earlier observation indicating that acetate inhibits tellurite uptake in R. capsulatus cells, as both anions compete for the same permease [18]. This evidence led to the proposal that in R. capsulatus tellurite enters the cell mainly through the acetate transport system (RcActP2) [17,19].…”

“…capsulatus is the acetate carrier ActP2, encoded by the actP2 gene [17], while the actP1 gene product , apparently, appears to have a minor role in the uptake of this oxyanion.…”

“…In R. capsulatus it has been shown that a mutant impaired in tellurite uptake became highly resistant to the oxyanion and the uptake defect was restored by the acetate permease actP2 gene [17], supporting an earlier observation indicating that acetate inhibits tellurite uptake in R. capsulatus cells, as both anions compete for the same permease [18]. This evidence led to the proposal that in R. capsulatus tellurite enters the cell mainly through the acetate transport system (RcActP2) [17,19]. Early work in E. coli cells [20] reported that phosphate transport mutants were characterized with higher resistance to TeO 3 2-and that the oxyanion was a potent inhibitor of A C C E P T E D M A N U S C R I P T which identifies in the homodimeric structure of ActP2 a signature of the strong tellurite uptake activity shown by this permease, namely a 15 amino acids insert that is missing in all ActP1 type permeases.…”

Fructose increases the resistance of Rhodobacter capsulatus to the toxic oxyanion tellurite through repression of acetate permease (ActP)

“…Notably, photosynthetic-anaerobically grown cells show a very high minimal inhibitory concentration (MIC) for tellurite ([800 lM) while dark-aerobically grown cells show an extremely low MIC for tellurite (%8 lM) (Borghese et al 2004). It was shown that intermediates of the TCA cycle such as malate, succinate or fumarate, when used as growth carbon sources, make the cells very sensitive to tellurite; conversely, other metabolites such as pyruvate or acetate drastically increase the MIC for the oxyanion by competing with tellurite for the same entry port (Borghese et al 2008), which has been identified as an acetate permease (ActP) (Borghese and Zannoni 2010).…”

“…To investigate on the expression of actP gene in cells grown on different carbon sources, the reporter gene lacZ was fused to the previously cloned acetate permease gene (actP) (Borghese and Zannoni 2010), giving plasmid pRB71 that carries lacZ fused to the first portion of the operon that includes acs (acetylCoA synthetase) and actP (see Supplementary Material). As shown in Fig.…”