Copper mobilisation from Cu sulphide minerals by methanobactin: Effect of pH, oxygen and natural organic matter

Abstract

Aerobic methane oxidation (MOx) depends critically on the availability of copper (Cu) as a crucial component of the metal centre of particulate methane monooxygenase, one of the main enzymes involved in MOx. Some methanotrophs have developed Cu acquisition strategies, in which they exude Cu-binding ligands termed chalkophores under conditions of low Cu availability. A well-characterised chalkophore is methanobactin (mb), exuded by the microaerophilic methanotroph Methylosinus trichosporium OB3b. Aerobic methanotrophs generally reside close to environmental oxic-anoxic interfaces, where the formation of Cu sulphide phases can aggravate the limitation of bioavailable Cu due to their low solubility. The reactivity of chalkophores towards such Cu sulphide mineral phases has not yet been investigated. In this study, a combination of dissolution experiments and equilibrium modelling was used to examine the dissolution and solubility of bulk and nanoparticulate Cu sulphide minerals in the presence of mb as influenced by pH, oxygen and natural organic matter. In general, weshow that mb is effective at increasing the dissolved Cu concentrations in the presence of a variety of Cu sulphide phases that may potentially limit Cu bioavailability.More Cu was mobilised per mole of mb from Cu sulphide nanoparticles compared with well-crystalline bulk covellite (CuS). In general, the efficacy of mb at mobilising Cu from Cu sulphides is pH-dependent. At lower pH, e.g. pH 5, mb was ineffective at solubilizing Cu. The presence of mb increased dissolved Cu concentrations between pH 7 and 8.5, where the solubility of all Cu sulphides is generally low, both in the presence and absence of oxygen. These results suggest that chalkophore-promoted Cu mobilisation from sulphide phases is an effective extracellular mechanism for increasing dissolved Cu concentrations at oxic-anoxic interfaces, particularly in the neutral to slightly alkaline pH range. This suggests that aerobic methanotrophs may be able to fulfil their Cu requirements via the exudation of mb in natural environments where the bioavailability of Cu is constrained by very stable Cu sulphide phases.

Rare methanotrophs adapt to broader environmental gradients than abundant methanotrophs in the riparian zone of the Three Gorges Reservoir

“…Finally, pH influences changes in the soil nutrient content and regulates the nutrient uptake of methanotrophs. One study found that a neutral pH range was the ideal living environment for most methanotrophs (Rushworth et al, 2022). There are two mechanisms by which soil pH can affect the assembly of methanotrophic communities—by directly affecting the growth of methanotrophs or by indirectly influencing plants to form methanotrophic communities (Li, Lijuan, et al, 2023; Martin‐Guay et al, 2022).…”

Multiple Mechanisms for Copper Uptake by Methylosinus trichosporium OB3b in the Presence of Heterologous Methanobactin

“…In any regard, copper uptake using MBs is an important mechanism for methanotrophs to collect this essential trace element from the environment lack of bioavailable copper. For example, MB-OB3b can extract copper from copper-sulfide minerals typically assumed to be biologically unavailable ( 46 ). Here, we demonstrate that the model methanotroph M. trichosporium OB3b can not only secrete and uptake its own MB but also has developed multiple mechanisms to take up copper in the presence of heterologous methanobactin MB-SB2, including initiating transcription of an alternative TBDT.…”

Weathered granites and soils harbour microbes with lanthanide-dependent methylotrophic enzymes

“…Copper is released from rocks by natural weathering processes before precipitating as non-bioavailable secondary minerals such as chalcocite (Cu 2 S) (K spa 6 × 10 −16 ). Under Cu limiting conditions, M. trichosporium OB3b produces chalkophore (methanobactin) [ 3 ] to dissolve Cu mineral phases [ 4 ]. Chalkophores also have affinities beyond Cu including Cd, Co, Fe, Mn, Ni, Zn and Pb, U [ 5 ].…”