Both pH and carbon flux influence the level of rubredoxin in Clostridium butyricum

The rubredoxin expression level in Clostridium butyricum DSM 5431 grown in continuous culture was monitored using primer extension analyses of the rub gene and a specific enzymatic assay of the iron-sulfur protein. In this wa y, we showed that variations in rubredoxin content and in rub mRNA level we re influenced by the pH of the culture and were directly dependent on the c arbon flux. The maximum rubredoxin level reached 1227.3 pmol (mg of protein s)(-1) (i.e. 0.7% of the total protein content) under strictly anaerobic co nditions when cells grew at pH 6.5 with an excess of glucose. In addition, primer extension analyses established that the control for all the variatio ns observed operates at the level of gene transcription. Altogether, these results suggested a main function of rubredoxin in Clostridium butyricum in dependent of the protection against oxygen as has already been reported for Desulfovibrio gigas and Pyrococcus furiosus.