Natural Organic Matter as Global Antennae for Primary Production

Abstract

Humic substances (HS) are high-molecular-weight complex refractory organics that are ubiquitous in terrestrial and aquatic environments. While resistant to microbial degradation, these compounds nevertheless support microbial metabolism via oxidation or reduction of their (hydro)quinone moieties. As such, they are known to be important electron sinks for respiratory and fermentative bacteria and electron sources for denitrifying and perchlorate-reducing bacteria. HS also strongly promote abiotic reduction of Fe(III) when irradiated with light. Here, we show that HS-enhanced Fe(III) photoreduction can also drive chemolithotrophic microbial respiration by producing Fe(II), which functions as a respiratory electron donor. Due to their molecular complexity, HS absorb most of the electromagnetic spectrum and can act as broad-spectrum antennae converting radiant energy into bioavailable chemical energy. The finding that chemolithotrophic organisms can utilize this energy has important implications for terrestrial, and possibly extraterrestrial, microbial processes and offers an alternative mechanism of radiation-driven primary productivity to that of phototrophy.

A Systematic Study of the Antioxidant Capacity of Humic Substances against Peroxyl Radicals: Relation to Structure

“…Although carbohydrates and polysaccharides represent an important and abundant class of free radical scavengers [ 6 , 31 , 34 , 66 , 67 , 68 , 69 , 70 , 100 ], these non-phenolic antioxidants are not considered to be strong antioxidants due to their low content of electron-donating aldehyde or ketone groups in the structure [ 52 ]. Besides, the observed antioxidant activity in this case is often related to impurities such as phenolic and/or protein components rather than to the carbohydrate moieties themselves [ 39 , 40 , 52 ].…”

“…Consolidated resources of humic materials are deposited mostly in peat, coal, composts, and sapropel [ 3 ]. HS are produced in situ due to chemical, physical, and microbial degradation, as well as (re)polymerization of phenolic and aromatic components such as lignin, tannins, polysaccharides, lipids, and proteins [ 4 , 5 , 6 ]. They have a non-stoichiometric elemental composition, irregular structure, and heterogeneous molecular composition [ 7 ].…”

Interactions between Humic Substances and Microorganisms and Their Implications for Nature-like Bioremediation Technologies

“…HSs are produced in situ due to chemical, physical, and microbial degradation, as well as (re)polymerization of phenolic and aromatic components such as lignin, tannins, and secondary metabolites [ 17 , 33 , 34 ]. They represent the dominant form of organic matter (OM) in the environment and are ubiquitous in marine, aquatic, soil, and sedimentary ecosystems, incorporating up to 94% of the total organic carbon [ 1 , 3 ].…”

Avaliação cromatográfica e estudos de sorção e de toxicidade em minhocas de deltametrina, glifosato e ácido aminometilfosfônico

“…São elas: huminafração insolúvel em meio aquoso, independente da acidez, ácidos húmicosinsolúvel em meio ácido diluído e ácidos fúlvicossolúvel em meio alcalino e ácido. [110], [151] As SH consistem de um esqueleto de unidades alquil/aromáticas ligadas principalmente por grupos oxigênio e nitrogênio, onde os principais grupos funcionais são ácidos carboxílicos e fenólicos, grupos hidroxilo alcoólicos, cetonas, e grupos de quinona. Acredita-se que se formam a partir da oxidação de biopolímeros no ambiente, assim como reações de condensação envolvendo moléculas orgânicas de baixa massa molecular.…”

“…Acredita-se que se formam a partir da oxidação de biopolímeros no ambiente, assim como reações de condensação envolvendo moléculas orgânicas de baixa massa molecular. [151] A interação da deltametrina e do glifosato com os ácidos húmicos Os principais grupos de absorção no infravermelho (região 400 -4000 cm -1 ) nas substâncias húmicas são observados na Tabela 52:…”