When aerobically grown C. glutamicum R cells are packed to a high density under oxygen-deprived conditions, despite the cessation of cellular growth, the cells remain able to excrete significant amounts of several metabolites such as lactate or succinate¹⁾. In this study we investigated the transcriptional profiling of the metabolism of O₂-deprived C. glutamicum. The glucose consumption rate per cell was higher than that achieved by cells incubated under aerobic conditions. Furthermore, DNA microarray and quantitative RT-PCR analyses revealed that the genes encoding several key enzymes involved in the glycolytic and organic acid production pathways, including gapA, pgk, tpi, ppc, ldhA and mdh, were significantly up-regulated under oxygen deprivation. The corresponding enzymatic activities consistently correlated to the regulation patterns of the genetic expression observed at the transcriptional level. Studies of lacZ fusions with gapA, ldhA and mdh indicated not only that these genes are strongly induced at the onset of the stationary phase under aerobic growth conditions, but also that the high expression levels are maintained under oxygen deprivation. These results indicate that the genetic expression of several key metabolic enzymes in C. glutamicum cells incubated under oxygen deprivation is chiefly regulated at the transcriptional level. The physiological consequence of the observed increased transcription under oxygen deprivation is an increased rate of carbon source consumption, which is accompanied by a increase in organic acids production.

This work was financially supported in part by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

1) J. Mol. Microbiol. Biotechnol. 7: 182-196. 2004.