Presence of Extracellular NAD⁺ and NADH in Cultures of Wood-Degrading Fungi

Abstract

Our previous studies indicated that extracellular glycoproteins produced by some white-rot and brown-rot basidiomycetous fungi reduce Fe(III) to Fe(II) and O 2 to H 2 O 2 and produce hydroxyl radicals. The continuous generation of hydroxyl radicals requires a constant supply of O 2 and an electron donor for the reduction of oxidized forms of the glycoproteins to the reduced forms. However, electron donors for this reaction, such as NADH, have not been identified. In this study, the amounts of the extracellular pyridine coenzymes, NAD and NADH, were measured in agar cultures of four white-rot fungi, one brown-rot fungus, and three soft-rot fungi. The sums of NAD and NADH detected in wood-containing cultures of all five basidiomycetes were greater than those in glucose cultures. The amounts of NAD were higher than those of NADH in all wood-containing cultures except that of Irpex lacteus, and NAD was greater than NADH in all glucose cultures except that of Fomitopsis palustris. Significant amounts of pyridine coenzymes were present in glucose and wood-containing cultures of the three soft-rot fungi. The non-wood-degrading fungus, Penicillium funiculosum, did not produce NAD or NADH in either glucose or wood-containing cultures. The extracellular pyridine coenzyme levels were relatively high compared to the rates of extracellular hydroxyl radical generation in wood-degrading fungal cultures. Thus, white-, brown-, and soft-rot fungi produce pyridine coenzymes that could serve as electron donors for the production of hydroxyl radicals during wood degradation.Key words White-rot fungi / Brown-rot fungi / Soft-rot fungi / Hydroxyl radical / NAD and NADH.

Electron Communication of Bacillus subtilis in Harsh Environments

“…Most energy-producing processes require coenzymes such as NAD, a highly abundant cellular component of bacteria that participates in electron transfer during oxidation-reduction reactions, which convert the oxidized form NAD into NADH, a strong reducing agent (Chini et al., 2017, Kido et al., 2015). NAD is oxidized or reduced by the loss or gain of two electrons, in reactions involving the removal of two hydrogen atoms (a “hydride ion” and a proton).…”

“…Secretion of NAD to the extracellular milieu has been reported in diverse species, such as E . coli , Rhodobacter capsulatus (Ying, 2006), and microorganisms in activated sludge (Wos and Pollard, 2009), as well as by wood-degrading fungi and animal cells (Kido et al., 2015, Xiao et al., 2018). The redox activity of this molecule suggests its participation in efficient electron transport and extracellular turnover of NADH to NAD + (Wos and Pollard, 2009).…”

MopA, the Mn Oxidizing Protein From Erythrobacter sp. SD-21, Requires Heme and NAD+ for Mn(II) Oxidation

“…A localization of MopA outside of the cell seems at odds with a physiological role for NAD + . Wood degrading fungi have been shown to excrete NAD + /NADH ( Kido et al, 2015 ), but we are unaware of any similar studies demonstrating bacteria secrete the dinucleotide, although extracellular bacterial enzymes requiring NAD + /NADH have been described ( Lee et al, 1995 ; Diaz et al, 2013 ). If intracellular NAD + is involved in electron transfer, quinones could transfer electrons from a loosely membrane bound or periplasmic MopA to intracellular NAD + [as suggested for extracellular NADH stimulated superoxide production ( Diaz et al, 2013 )], and PQQ may be serving a similar role in the assay, resulting in its stimulatory effect.…”

Transcriptome and Secretome Analyses of the Wood Decay Fungus Wolfiporia cocos Support Alternative Mechanisms of Lignocellulose Conversion

“…Although roles for GLPs, oxalate decarboxylase, and CRO5 might be envisioned for a Fenton-based system (e.g., in Fe 3ϩ reduction, metal ion speciation, and peroxide generation, respectively), the mechanistic details are very much uncertain. In the case of GLP, Amadori-modified amino acids in GLP are proposed to serve as redox centers mediating ferric ion and oxygen reduction (34), while NADH is suggested as the physiological source of reductant based on detection of the dinucleotide in cultures (41). Production of other low-molecular-weight Fe 3ϩ -reducing compounds has been characterized in W. cocos cultures, which produce both hydroxamate-type and catechol-type chelators (14), as do other brown-rot fungi (see reference 10 for a review).…”