Effect of hydrogen peroxide and carbon-to-nitrogen ratio on growth and biochemical profile in oleaginous Mucoromycota
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Background Hydrogen peroxide (H 2 O 2 ) plays a crucial role in biology of both redox reactions and oxidative stress. In some ranges of concentrations, H 2 O 2 can work as a signaling molecule, triggering specific metabolic pathways. Some works have explored the influence of H 2 O 2 and other stress molecules in lipid accumulation. Additionally, H 2 O 2 has gained attention as cofactor of lytic polysaccharide monooxygenases (LPMOs) during lignocellulose saccharification. The action of these enzymes demonstrated to enhance significantly the saccharification efficiency. However, in simultaneous saccharification and fermentation (SSF) processes H 2 O 2 can have deleterious effects on the fermenting microorganism. In this study, nine strains from eight different species of Mucoromycota were grown at different sublethal concentrations of H 2 O 2 and two carbon-nitrogen (C/N) ratios. The aim of this study was to investigate if H 2 O 2 could be used in Mucoromycota SSF processes and to identify which possible effects, beneficial or deleterious, could occur under different C/N conditions. Results In general, all the strains tolerated H 2 O 2 at much higher concentrations than those commonly used to improve enzymatic saccharification (1-19 mM vs 1-240 µM). Infrared spectroscopy was used to analyze the biochemical composition of the fungi. The exposure to sublethal H 2 O 2 doses did not increase any metabolite in particular but slightly reduced biomass production at concentrations near the minimal inhibitory concentration (MIC) in some cases. For Lichtheimia corymbifera grown in standard C/N medium, an accumulation of intracellular proteins with oxidative damage was positively correlated to the H 2 O 2 concentration. This was not observed for other strains. The biggest changes in the biochemical composition of the fungal biomass were linked to changes in medium C/N ratios. This included different carbon allocation strategies among the tested species, such as allocation towards lipids and polyphosphates, lipids and saccharides, etc. Conclusions Our results suggest that the Mucoromycota strains here are compatible with H 2 O 2 feeding in lignocellulose-based SSF to enhance efficiency while sustaining minimal oxidative damage.
