Thermodynamic energy of anaerobic microbial redox reactions couples elemental biogeochemical cycles

Abstract

Purpose The thermodynamic energy of redox reactions affects the distribution of microbial redox reactions and cyclic transformation of elements in various anaerobic ecosystems. The principle of thermodynamics is of dramatic significance in understanding the energetics of metabolic processes, the biogeochemical behavior of microorganisms, and mass and energy cycles. The purpose of this paper is to relate the distribution of the coupling reactions between C, N, Fe, and S, the most important elements involved in microbially mediated redox reactions, with their thermodynamic feasibility to provide theoretical foundation of their occurrence. Results and discussion Anaerobic microorganisms catalyze diverse redox reactions in anoxic environments, driving elemental biogeochemical cycles on the earth. They capture energy from catalyzing these redox reactions in order to support life. The thermodynamic feasibility of these microbe-driven redox reactions is controlled by their energy yields which depend on environmental conditions. Anaerobic microorganisms can oxidize organic carbon with diverse inorganic compounds including nitrate/nitrite, ferric iron, and sulfate as electron acceptors in various anoxic environments which is referred to anaerobic respiration of organic matter; reversely, inorganic carbon can be reduced to synthesize cell material with ferrous iron and sulfide as an alternative electron donor by phototrophs under different sets of circumstances. Nitrate/nitrate can be microbically reduced by inorganic compounds such as ferrous iron and sulfide under some specific situations; the coupling of anaerobic anammox oxidation and reduction of nitrite (anammox), ferric iron (feammox), and sulfate (suramox) driven by anaerobes occurs in other particular systems. Conclusions and perspectives Although there are increasing researches investigating the anaerobe-driven coupling of pairs of elements such as C-N, C-Fe, C-S, N-Fe, N-S, and Fe-S, much more intricate situations associating the coupling of multiple elements are still not comprehensively understood. A great many reactions which are thermodynamically feasible have not yet been identified in natural environments or laboratories. Further work focusing on the metabolic pathways from a genetic and enzymatic perspective and the factors controlling the feasibility of the reactions by using updated technical tools and methods is required.

Understanding Microbial Arsenic-Mobilization in Multiple Aquifers: Insight from DNA and RNA Analyses

“…Several strategies of Fe­(III) reducers could be utilized to facilitate the accessible solid iron as an electron acceptor, including direct cell–mineral contact, utilizing chelating agents or microbial/environmental redox-active electron shuttles, electron hopping, and microbial nanowires . Microbially catalyzed Feammox could potentially mobilize As via the reductive dissolution of sedimentary Fe­(III) minerals, which was recently evidenced by N and O isotopic analyses of nitrogen sources and nitrogen transformations in high As aquifers. , Thauera spp., associated with higher transcription levels in the groundwater-sourced (other than sediment-sourced) active microbial community, can use ammonium salts as the nitrogen source − and reduce Fe­(III) oxides (such as Thauera humireducens SgZ-1), potentially supporting the Feammox process. ,, Sulfur disproportionation has also been evidenced by S and O isotopic analyses, critically causing As mobilization in the study area . S-Disproportionators ( Desulfurivibrio , Desulfobulbus , and Desulfocapsa ) were also more specifically active in groundwater-sourced than sediment-sourced microbial communities.…”

“…22,66,67 Moreover, sulfate reduction can couple with ammonium oxidation (termed Surammox), producing reduced sulfur compounds (i.e., sulfide and/or element sulfur), which may facilitate As immobilization 68 and/or mobilization. 7,69 The significant variations in groundwater chemistry might infer diverse As-mobilizing N-, S-, As-, and Fe-related biogeochemical processes in the western Hetao basin aquifers studied here.…”

“…Moreover, ammonium was positively correlated with TAs ( r = 0.895 and p = 0.016), Fe­(II) ( r = 0.746 and p = 0.067), and sulfate (Figure a) ( r = 0.863 and p = 0.023) (Figure a). Previous studies showed that ammonium oxidation coupled with Fe­(III) reduction (termed Feammox) may result in As mobilization via the reductive dissolution of As-bearing Fe­(III) (hydro)­oxides. ,, Moreover, sulfate reduction can couple with ammonium oxidation (termed Surammox), producing reduced sulfur compounds (i.e., sulfide and/or element sulfur), which may facilitate As immobilization and/or mobilization. , The significant variations in groundwater chemistry might infer diverse As-mobilizing N-, S-, As-, and Fe-related biogeochemical processes in the western Hetao basin aquifers studied here.…”

“…can be involved in Fe(III) reduction (such as Thauera humireducens SgZ-1), 88 potentially supporting the Feammox process. 9,22,69 The Desulfosporosinus, Desulfovibrio, and Desulfobulbus species were detected and positively correlated with sulfide, which have been reported to be involved in sulfate (and also Fe(III)) reduction. 27,89 Desulfovibrio spp.…”

Interactions of the sulfur and nitrogen cycles: microbiology and process technology

“…A new process for simultaneous anaerobic ammonium oxidation and sulfate reduction was observed for the first time by Fdz-Polanco et al (2001)during anaerobic treatment of vinassewho noticed that 50% of the nitrogen entering the reactor as total Kjeldahl nitrogen (TKN) was found as N 2 in the gas phase, and at the same time, 20% of the SO 4 2− originally present in the influent appears as S 2− in the effluent or H 2 S in the gas, with a sulfur removal efficiency of 80%. Fdz-Polanco et al (2001) proposed the following as a possible pathway: There is no evidence yet that anammox bacteria possess the ability to oxidize ammonium with sulfate as an electron donor (Wang et al, 2017;Bi et al, 2020). Other studies confirmed, nevertheless, the pathway described in Equation 13.13 (Yang et al, 2009;Rios-Del Toro et al, 2018) even at low temperatures (14-15°C) (Wu et al, 2020).…”