Redox chemistry of molybdenum in natural waters and its involvement in biological evolution

Abstract

The transition element molybdenum (Mo) possesses diverse valances (+II to +VI), and is involved in forming cofactors in more than 60 enzymes in biology. Redox switching of the element in these enzymes catalyzes a series of metabolic reactions in both prokaryotes and eukaryotes, and the element therefore plays a fundamental role in the global carbon, nitrogen, and sulfur cycling. In the present oxygenated waters, oxidized Mo(VI) predominates thermodynamically, whilst reduced Mo species are mainly confined within specific niches including cytoplasm. Only recently has the reduced Mo(V) been separated from Mo(VI) in sulfidic mats and even in some reducing waters. Given the presence of reduced Mo(V) in contemporary anaerobic habitats, it seems that reduced Mo species were present in the ancient reducing ocean (probably under both ferruginous and sulfidic conditions), prompting the involvement of Mo in enzymes including nitrogenase and nitrate reductase. During the global transition to oxic conditions, reduced Mo species were constrained to specific anaerobic habitats, and efficient uptake systems of oxidized Mo(VI) became a selective advantage for current prokaryotic and eukaryotic cells. Some prokaryotes are still able to directly utilize reduced Mo if any exists in ambient environments. In total, this mini-review describes the redox chemistry and biogeochemistry of Mo over the Earth’s history.

High Molybdenum availability for evolution in a Mesoproterozoic lacustrine environment

“…This implies a high potential for the sequestration of metals as sulphides, a possibility which merits further research. The Stoer Group data are also consistent with evidence for a greater diversity of eukaryotes in marginal marine environments compared with offshore marine environments, which was hypothesized to reflect the scarcity of Mo in offshore waters distant from continental run-off 13 .The availability of trace metals was a key influence on the development of multicellular life 57,64 , and Mo-dependent enzymes in particular are essential to eukaryotic cell biology 57,58,[64][65][66] . The evolution of Mo usage is regarded as a fundamental aspect of the diversification of eukaryotes, probably from 1.5 to 1.0 Ga (ref.…”

“…The evolution of Mo usage is regarded as a fundamental aspect of the diversification of eukaryotes, probably from 1.5 to 1.0 Ga (ref. 58). The data reported here show that Mo was readily available to support such a diversification in the terrestrial environment at this critical time.…”

“…An important control on high Mo levels ARTICLE in the Stoer Group was the high content of sulphide in the lake water, which reflects a high enough level of atmospheric oxygenation to allow ready weathering of sulphides on the continents 36 and hence the ready availability of sulphate to surface environments in the late Mesoproterozoic. Mo is essential to biological N fixation [57][58][59] , so the record of Mo availability to the Stoer Group lake supports models in which N-fixing cyanobacteria could flourish in the Mesoproterozoic lacustrine environment while being inhibited in the ocean. The high burial rates for Mo in the Stoer Group could be interpreted to imply a high concentration of Mo in the water column, assuming steadystate conditions.…”

A combined Y/Ho, high field strength element (HFSE) and Nd isotope perspective on basalt weathering, Deccan Traps, India

“…Within the Chhindwara profile, U mobility greater than that of the other HFSE is evident through the scatter and U loss expressed by the U/Nb ratio that is superimposed on the compositional variation between the upper and lower flow ], respectively, in natural waters. In contrast to U, however, these elements serve a biological function as metal cofactors in enzymes (e.g., Kletzin and Adams, 1996;Hille, 2002;Anbar, 2004;Andreesen and Makdessi, 2008;Wang, 2013). It is therefore possible that changes in their oceanic supplies and/or sinks may have exerted a limiting control on the evolution of oceanic biota and their respiration mechanisms.…”

Mo and Ni Removal from Drinking Water Using Zeolitic Tuff from Jordan

“…Mo is an essential element in animal and plant nutrition and is ubiquitous in food and water as soluble molybdates [4]. It is involved in forming cofactors in more than 60 enzymes in biology [5]. Humans need 25 µg·day −1 Mo [6].…”