Mineral-Bound Trace Metals as Cofactors for Anaerobic Biological Nitrogen Fixation

Abstract

Nitrogenase is the only known biological enzyme capable of reducing N2 to bioavailable NH3. Most nitrogenases use Mo as a metallocofactor, while alternative cofactors V and Fe are also viable. Both geological and bioinformatic evidence suggest an ancient origin of Mo-based nitrogenase in the Archean, despite the low concentration of dissolved Mo in the Archean oceans. This apparent paradox would be resolvable if mineral-bound Mo were bioavailable for nitrogen fixation by ancient diazotrophs. In this study, the bioavailability of mineral-bound Mo, V, and Fe was determined by incubating an obligately anaerobic diazotroph Clostridium kluyveri with Mo-, V-, and Fe-bearing minerals (molybdenite, cavansite, and ferrihydrite, respectively) and basalt under diazotrophic conditions. The results showed that C. kluyveri utilized mineral-associated metals to express nitrogenase genes and fix nitrogen, as measured by the reverse transcription quantitative polymerase chain reaction and acetylene reduction assay, respectively. C. kluyveri secreted chelating molecules to extract metals from the minerals. As a result of microbial weathering, mineral surface chemistry significantly changed, likely due to surface coating by microbial exudates for metal extraction. These results provide important support for the ancient origin of Mo-based nitrogenase, with profound implications for coevolution of the biosphere and geosphere.

Exploring the influence of atmospheric CO2and O2levels on the utility of nitrogen isotopes as proxy for biological N2fixation

“…The lowest levels of Mo are encountered in rivers, freshwater lakes and estuaries (Pizarro et al, 2014), as well as in tropical soils (Barron et al, 2009), with the modern ocean Mo levels ranging from 2-108 nM (Pizarro et al, 2014; Zerkle et al, 2006; Zerkle et al, 2008). Given the 2-3 ppm Mo in the Earth’s crust (McLennan, 2001), with some strains like A. variabilis able to extract Mo from silicates using metallophores (Liermann et al, 2005), BNF organisms are thought to be able to access sufficient Mo to meet their needs (Sheng et al, 2023). Mo at 10 µM and 1 µM also stimulated BNF in the archaeon, Methanosarcina barkerei 227, in the absence of NH 4 + or glutamate (Lobo & Zinder, 1988).…”

Differential degradation of petroleum hydrocarbons by Shewanella putrefaciens under aerobic and anaerobic conditions

“…In brief, the threshold cycle (Ct) values for both the target (ubiD) and reference genes (16S rRNA) were obtained via qPCR across different samples. The expression of the target gene was then adjusted based on the Ct value of the reference gene ( Sheng et al, 2023 ). The fold change in gene expression was determined using the 2 -ΔΔCt method, a well-established technique for relative quantification ( Livak and Schmittgen, 2001 ; Vaishnav et al, 2022 ).…”

Effects of aeration modes and rates on nitrogen conversion and bacterial community in composting of dehydrated sludge and corn straw

“…The moisture content (MC), pH, and germination index (GI) were determined with reference to the Chinese National Standard (NY 525-2021). The organic carbon and total nitrogen were tested by an element analyzer ( Sheng et al, 2023 ). The nitrate nitrogen content, ammonium nitrogen content, and amide nitrogen content were measured with the reference to the Chinese National Standard (NY/T 1116-2014).…”