The Life Evolution on the Sulfur Cycle: From Ancient Elemental Sulfur Reduction and Sulfide Oxidation to the Contemporary Thiol-Redox Challenges

Abstract

Organismal evolution led to innovations in metabolic pathways, many of which certainly modified the surface chemistry of the Earth. Volcanic activity introduced inorganic compounds (H 2 , CO 2 , CH 4 , SO 2 , and H 2 S) driving the metabolism of early organisms of the domains archaea and bacteria. In the absence of light, H 2 S and Fe 2+ would have been the major electron donors and the electron acceptors could be either oxidized species such as the sulfurs, sulfate, and elemental sulfur, or carbon dioxide by the fermentation of acetate (forming methane). Elemental sulfur was produced by the reaction between H 2 S and SO 2 , while anoxygenic photosynthesis may have provided the sulfate which removed oceanic ferrous iron by its precipitation as sulfide into sediments. Hence, the sulfur cycle participation in life evolution comes from ancient anoxygenic elemental sulfur reduction generating environmental sulfide incorporated as mitochondrial Fe-S for the electrontransport chains. Anoxygenic photosynthesis may have provided the necessary sulfate to promote the evolution of sulfate-reducing bacteria. The evolution of oxygenic photosynthesis provided for diverse metabolic possibilities including non-photosynthetic sulfide oxidation, nitrification, and methanotrophy. An increase in oxygen levels would account for oxidative sulfur cycle, evolution of colorless sulfur bacteria, and emergence of large multicellular animals. Oxygen, initially a waste product of photosynthesis, first reacted with sulfur, iron or methane and latter accumulated in atmosphere resulting in more carbon production. Oxygenic photosynthesis becomes a positive feedback on the oxidation of the Earth-surface environment causing the growth and stabilization of continental platforms and carbon burial with more atmosphere oxidation. An increase in oxygen levels would account for oxidative sulfur cycle, evolution of colorless sulfur bacteria, and emergence of large multicellular animals. Oxygen enabled more efficient energy transformation from dietary food to ATP. However, evolution for mammals living on dry land has been closely linked to the adaptation of changes in O 2 concentration in the environment, which means mitochondrial aerobic respiration. By using ancestral geochemistry of iron-sulfur clusters at the protein complexes I and II, the respiratory chains become

Is biofilm formation intrinsic to the origin of life?

“…Indeed, also other fundamental metabolic processes such as anoxygenic photosynthesis thought to represent one of the earliest forms of metabolism and an alternative mode of energy conservation using light as the external energy sources is based on the oxidation of Fe 2+ to Fe 3+ (Ozaki et al, 2019 ; Xiong et al, 2000 ). Furthermore, Fe 3+ has been recognized as the most ancient and a central electron acceptor in respiration (Vargas et al, 1998 ) and Fe 2+ is in a reverse reaction also used as an electron donor (Burini et al, 2018 ). Moreover, biofilms form even today on metal sulfides and sulfur, the second central redox‐active compound enabling ancient metabolism.…”

Biofilm formation is intrinsic to the origin of life

“…Indeed, also other fundamental metabolic processes such as anoxygenic photosynthesis thought to represent one of the earliest forms of metabolism and an alternative mode of energy conservation using light as the external energy sources is based on the oxidation of Fe 2+ to Fe 3+ [61,62]. Furthermore, Fe 3+ has been recognized as the most ancient and a central electron acceptor [63] and Fe 2+ is in a reverse reaction also used as an electron donor [64]. Furthermore, biofilms form even today on metal sulfides and sulfur, the second central redox-active compound enabling ancient metabolism.…”

Computational Study of Base-Catalyzed Thiohemiacetal Decomposition in Pseudomonas mevalonii HMG-CoA Reductase

“…Sulfur-based compounds play a key role in biochemical processes of prokaryotic and eukaryotic cells. − These compounds serve a broad range of purposes from serving as building blocks in fatty acid biosynthesis to post-translational modification. , Enzymes have also evolved to make and manipulate the carbon–sulfur bonds . For example, cysteine residues in catalytic sites can serve as nucleophiles for acyl groups resulting in the formation of thiohemiacetalsa common tetrahedral intermediate .…”