Responses of Saccharomyces cerevisiae to changing oxygen level

We studied the responses of Saccharomyces cerevisiae in varying oxygen concentrations on metabolite, transcriptome and proteome level. The S. cerevisiae strain CEN.PK113-1A was grown in D-glucose-limited chemostat cultures in five different oxygen concentrations: 0%, 0.5%, 1%, 2.8% and 20.9% O2 of the inlet gas. After reaching a steady state the oxygen was shut off from the cultures of 1% and 20.9% O2 of the inlet gas and the metabolism followed for approximately 70 hours. From both steady state and transient culture samples 17 metabolites of central carbon metabolism were analyzed. Changes in the transcriptome were monitored with Affymetrix-arrays and with the VTT-TRAC method. In addition, alterations in the proteome were analyzed with 2-D gels. The concentrations of metabolites of tricarboxylic acid cycle (TCA) and most glycolytic metabolites were, in general, higher in anaerobic or low aeration cultures (0%, 0.5% and 1% O2 of the inlet gas) compared with more aerobic conditions (2.8% and 20% O2 of the inlet gas). Similarly, after oxygen shut off from the cultures of 1% or 20.9% O2 of the inlet gas the level of TCA metabolites and those of upper glycolysis increased. On the transcriptome level the responses varied more, some genes being upregulated and others down regulated in steady state conditions and showing varying responses during transient conditions. As evaluated from both the metabolite and transcription data approximately 30 h was required to reach a new steady state of anaerobiosis.