Survivalin the absence of oxygen: A comparative assessment of the transcriptionalresponse of S. cerevisiae and the obligatory-aerobic filamentousfungus Trichoderma reesei for energy production under transit anoxicconditions.
Ari J. S. Ferreira, Eric D. Bonaccorsi, Marluce Mantovani, Hamza El-Dorry
Departmentof Biochemistry, Institute of Chemistry, Avenida Prof. Lineu Prestes 748, Sao Paulo SP 05508-900 Sao Paulo, Brazil
Oxygen is essential for the survival of obligatory-aerobic eukaryotic microorganism. Molecular aspects of why obligatory-aerobic microorganisms, such as the filamentous fungus Trichoderma reesei, are unable to survive under anoxic conditionare not fully characterized. Here we compare the expression profile of the transcripts of genes required for energy production, under anoxic condition, to those of the facultative anaerobic yeast S. cerevisiae. Using cDNA microarray, Northern analysis, and RealTime-PCR, we show that transit anoxia leads tostrong repression of critical genes in the glycolytic pathway, the expression of which would be essential for energy production under anaerobic condition. The majority of the genes of the TCA cycle showed a strong repression under anoxic condition. The strong repression of hexokinase, glucokinase, phosphofructokinase, triose phosphate isomerase, phosphoglycerate mutase, andpyruvate kinase prevents the flow of the metabolites from glucose to pyruvate. This transcriptional profile, therefore, will not permit this microorganism to produce ATP and generate NAD+ through anaerobic metabolism. In fact, under this anoxic condition, the production of CO2 and glucose consumption were interrupted. The transcriptional profile of the genes in the central carbon metabolism of T. reesei reveals basic difference between this obligatory aerobic microorganism and the facultative anaerobic S. cerevisiae in regards of energy production under anaerobic condition. While the genes of anaerobic energy production in S. cerevisiae were strongly induced in the absence of oxygen, critical genes in the glycolytic pathway were strongly repressed preventing T.reesei from ATP production and thus survival in the absence.