Cadmium uptake in Escherichia coli K-12

Abstract

109Cd2+ uptake by Escherichia coli occurred by means of an active transport system which has a Km of 2.1 microM Cd2+ and a Vmax of 0.83 mumol/min X g (dry weight) in uptake buffer. 109Cd2+ accumulation was both energy dependent and temperature sensitive. The addition of 20 microM Cd2+ or Zn2+ (but not Mn2+) to the cell suspensions preloaded with 109Cd2+ caused the exchange of Cd2+. 109Cd2+ (0.1 microM) uptake by cells was inhibited by the addition of 20 microM Zn2+ but not Mn2+. Zn2+ was a competitive inhibitor of 109Cd2+ uptake with an apparent Ki of 4.6 microM Zn2+. Although Mn2+ did not inhibit 109Cd2+ uptake, the addition of either 20 microM Cd2+ or Zn2+ prevented the uptake of 0.1 microM 54Mn2+, which apparently occurs by a separate transport system. The inhibition of 54Mn2+ accumulation by Cd2+ or Zn2+ did not follow Michaelis-Menten kinetics and had no defined Ki values. Co2+ was a competitive inhibitor of Mn2+ uptake with an apparent Ki of 34 microM Co2+. We were unable to demonstrate an active transport system for 65Zn2+ in E. coli.

Conditions for detecting the mutagenicity of divalent metals in Salmonella typhimurium

“…Although not all divalent metals have been studied with respect to their cell transport, the early work of Abelson and Aldous [1950], and the results presented in Table 11, suggest that the Mg++ transport system may be capable of transporting Co++, Fe++, Mn'+, Z n + + , and, to a lesser extent, C d + + As stated above, the ease of detecting the mutagenicity of these metals suggested two distinct groups, M n + + , Fe++, and Mn++, and Cd++ and Z n f + . In this context, it was reported by Laddaga and Silver [1985] that Cd++ was actively transported by E . coli, and that Zn++, but not M n i~+ , was a competitive inhibitor of Cd++ uptake, suggesting that the mutagenic groupings of metals may have a basis in their specific transport processes.…”

Copper and cadmium: responses inPseudomonas putidaKT2440

“…For Cu cell homoeostasis may involve a P-type ATPase, encoded by pacS and chelation by Cop and other binding proteins (Canovas et al 2003). For Cd, there is no specific predicted uptake system, rather it may enter microbial cells by transport systems for Mn (Tynecka et al 1981) or Zn (Laddaga and Silver 1985). Three loci for the Czc (Cd 2+ , Zn 2+ and Co 2+ ) chemiosmotic efflux systems are present (Hu and Zhao 2007).…”

Key genes involved in heavy-metal resistance inPseudomonas putidaCD2

“…It has been reported that Cd 21 damages the cells by a broad spectrum of effects on cell metabolism for instances by binding to essential respiratory enzymes (Nies, 2003), inducing oxidative stress (Banjerdkij et al, 2005) or inhibiting DNA repair (Jin et al, 2003). Cd 21 can easily enter bacterial cells by the transport systems for essential divalent cations such as Mn 21 (Tynecka et al, 1981) or Zn 21 (Laddaga & Silver, 1985), so almost all prokaryotes and eukaryotes have developed mechanisms to prevent excessive accumulation of Cd 21 in the cells. The relatively low intracellular Cd 21 concentration is maintained through the regulation of sequestration or efflux.…”