Inactivating alternative NADH dehydrogenases: enhancing fungal bioprocesses by improving growth and biomass yield?

Debate still surrounds the physiological roles of the alternative respiratory enzymes found in many fungi and plants. It has been proposed that alternative NADH:ubiquinone oxidoreductases (NADH dehydrogenases) may protect against oxidative stress, conversely, elevated activity of these enzymes has been linked to senescence. Here we show that inhibition of these enzymes in a fungal protein expression system (Aspergillus niger) leads to significantly enhanced specific growth rate, substrate uptake, carbon dioxide evolution, higher protein content, and more efficient use of substrates. These findings are consistent with a protective role of the NADH dehydrogenases against oxidative stress, thus, when electron flow via these enzymes is blocked, flux through the main respiratory pathway rises, leading to enhanced ATP generation. We anticipate that our findings will stimulate further studies in fungal and plant cultures leading to significant improvements in these expression systems, and to deeper insights into the cellular roles of alternative respiration

Synthesis of Extracellular L-lysine-α-oxidase along with Degrading Enzymes by <i>Trichoderma</i> cf. <i>aureoviride</i> Rifai VKM F-4268D: Role in Biocontrol and Systemic Plant Resistance

When cultivating on wheat bran or deactivated fungal mycelium as a model of “natural growth”, the ability of Trichoderma to synthesize extracellular L-lysine-α-oxidase (LysO) simultaneously with cell-wall-degrading enzymes (proteases, xylanase, glucanases, chitinases, etc.), responsible for mycoparasitism, was shown. LysO, in turn, causes the formation of H2O2 and pipecolic acid. These compounds are known to be signaling molecules and play an important role in the induction and development of systemic acquired resistance in plants. Antagonistic effects of LysO have been demonstrated against phytopathogenic fungi and Gram-positive or Gram-negative bacteria with dose-dependent cell death. The antimicrobial effect of LysO decreased in the presence of catalase. The generating intracellular ROS in the presence of LysO was also shown in both bacteria and fungi, which led to a decrease in viable cells. These results suggest that the antimicrobial activity of LysO is due to two factors: the formation of exogenous hydrogen peroxide as a product of the enzymatic oxidative deamination of L-lysine and the direct interaction of LysO with the cell wall of the micro-organisms. Thus, LysO on its own enhances the potential of the producer in the environment; namely, the enzyme complements the strategy of the fungus in biocontrol and indirectly participates in inducing SAR and regulating the relationship between pathogens and plants