Optimizing strategy for Escherichia coli growth and hydrogen production during glycerol fermentation in batch culture: Effects of some heavy metal ions and their mixtures

Highlights: • Effects of heavy metals on Escherichia coli were revealed during glycerol fermentation at pH 6.5. • Ni²⁺ + Fe²⁺ (0.05 mM) mixture stimulated up to 1.5-fold bacterial biomass yield. • Ni²⁺ + Fe³⁺ (0.05 mM), Ni²⁺ + Fe³⁺ + Mo⁶⁺ (0.02 mM) and Fe³⁺ + Mo⁶⁺ enhanced (up to 3-fold) H₂ production. • Discrimination between Fe²⁺ and Fe³⁺ was important for H₂ production. • Cu⁺ and Cu²⁺ (0.1 mM) inhibited H₂ production. - Abstract: Hydrogen (H₂) is well-known effective, ecologically clean and renewable fuel. Bacterial H₂ production is a promising one and its use in industrial level is expected to increase in the nearest future to establish sustainable and renewable energy source. Escherichia coli wild type BW25113 growth yield was shown to be stimulated 1.3–1.5-fold by nickel (Ni²⁺), iron (Fe²⁺, Fe³⁺) ions and by some metal ion mixtures: Ni²⁺ + Fe²⁺ + molybdenum (Mo⁶⁺), Ni²⁺ + Fe³⁺, Ni²⁺ + Fe²⁺ and Mo⁶⁺ + Fe³⁺ in low concentrations (<0.05 mM) stimulated the growth during glycerol (10 g L⁻¹) fermentation up to stationary phase at pH 6.5; Ni²⁺ + Fe²⁺ mixture showed the maximal effect. However, the same concentrations of these metals and their mixtures had no effects or slightly inhibited bacterial specific growth rate: it was suppressed ∼1.2-fold upon Ni²⁺, Fe³⁺, Mo⁶⁺ and Ni²⁺ + Mo⁶⁺ mixture supplementation. H₂ production by E. coli from glycerol was observed with the yield of 0.75 ± 0.02 mmol L⁻¹. Moreover, H₂ yield was markedly stimulated 1.7–3-fold in the presence of Ni²⁺ + Fe³⁺, Ni²⁺ + Fe³⁺ + Mo⁶⁺ and Fe³⁺ + Mo⁶⁺ mixtures, but not sole metals: maximal stimulation was established by Fe³⁺ + Mo⁶⁺ mixture with the concentrations of 0.05 mM and 0.02 mM, respectively. While copper (Cu⁺, Cu²⁺) ions in low concentration (0.1 mM) had H₂ production suppressing effect. The results point out that some heavy metal ions and their mixtures can stimulate E. coli growth, as well as enhance bio-hydrogen production. Discrimination between Fe²⁺ and Fe³⁺ was important for H₂ production. Some interaction of Ni²⁺ with Fe²⁺ was suggested to be effective factor increasing bacterial biomass and determining activity of H₂ producing hydrogenases together with Fe³⁺. Mo⁶⁺ was significant for H₂ production. The results obtained were important to develop H₂ production biotechnology using glycerol as cheap substrate and optimizing the technological conditions by some heavy metals and their mixtures at low concentrations.