Metal internalization by bacterial cells depends on metal biotoxicity and metal to biomass ratio

• Published in: Chemosphere (Oxford) 2018-12, Vol.212, p.585-593
• Main Authors: Liang, Lili, Ngwenya, Bryne T.
• Format: Article
• Language: English
• Subjects: Adsorption; Bacteria; Bacteria - pathogenicity; Biomass; Chelating Agents - chemistry; E. coli JM109; Escherichia coli - chemistry; Metal internalization; Uptake
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2018.08.125

The traditional view of metal adsorption to bacterial surfaces is that it can act as a protective mechanism by externalizing the metal outside the cell. However, numerous studies focussing on the biodynamics of metal uptake using biotic ligand models consider metal adsorption to cell surfaces as an important first step in metal uptake and internalization. In order to resolve these conflicting views, we adsorbed two metals (copper and cadmium) with contrasting metal biotoxicity on E. coli JM109, and quantified the distribution of each metal amongst surface sites, periplasmic space and the cytoplasm. Distribution of each metal depended on biotoxicity and metal to biomass ratio. For both metals, low metal to biomass ratio led to most of the metal being associated with the periplasmic space, with less Cd being taken up by cells overall. At high metal to biomass ratios, most of the Cd was associated with surface sites, whereas Cu also increased in surface sites but remained below periplasmic concentrations. These observations are consistent with metal internalization being the dominant process at low metal to biomass ratios, whereas was active efflux when metal to biomass was high, leading to equilibrium between cytoplasm and surface concentrations. Significantly, efflux was more intense for high biotoxicity Cd, consistent with active enzymatic regulation of Cu internalization/homeastasis, which is essential at low concentrations. Moreover, metal internalization increases as surface-bound metal increases, the maximum being constrained by maximum adsorption consistent with Langmuir adsorption behaviour. Bacterial metal internalization is a function of metal biotoxicity and metal loading. Metal internalization depends on metal biotoxicity and metal to biomass ratio. [Display omitted] •We characterized metal partitioning in different cellular compartments in bacteria.•Partitioning depends on biotoxicity of the metal.•It also depends on metal to biomass ratio.•Metal internalization increases as surface-bound metal increases.