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 ) has gained attention as cofactor of lytic polysaccharide monooxygenases (LPMOs) during lignocellulose saccharification. The action of these enzymes has been shown to significantly enhance saccharification efficiency. However, in simultaneous saccharification and fermentation (SSF) processes, H 2 O 2 can have deleterious effects on the fermenting microorganism. In addition to oxidative stress, at certain concentration ranges, H 2 O 2 can play a crucial role in redox biology mediating metabolic crosstalk. Indeed, some works have explored the influence of H 2 O 2 and other stress molecules in lipid accumulation. 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 whether H 2 O 2 could enhance lignocellulose-based SSF with oleaginous Mucoromycota fungi to produce second-generation biofuels. Therefore, effects of H 2 O 2 concentration, beneficial or deleterious, were identified 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). Vibrational spectroscopy (mid-infrared and Raman) 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 accumulation of lipids and polyphosphates, lipids and saccharides, etc.
Conclusions
Our results suggest that the Mucoromycota strains used in this study are compatible with H 2 O 2 feeding in lignocellulose-based SSF to enhance efficiency while sustaining minimal risk of oxidative damage.
