Ferredoxin degradation in growing Clostridium pasteurianum during periods of iron deprivation

Clostridium pasteurianum was grown in batch cultures on media with an initial iron concentration of 10 M. The uptake of iron and the synthesis of ferredoxin was followed. All the iron present in the medium was taken up by the cells before 50% of the final cell density was attained. The bacteria then continued to grow in the complete absence of exogenous iron. Ferredoxin was synthesized during growth until the exogenous iron concentration dropped below 1 M. During growth in the absence of iron ferredoxin was degraded with the result that at the end of growth the cells did not contain ferredoxin. The specific activity of the iron sulfur protein, pyruvate synthase (E.C. 1.2.7.1), remained constant during growth of C. pasteurianum in the absence of exogenous iron. This finding suggests that ferredoxin was used as an endogenous source of iron for the synthesis of essential iron proteins during periods of iron deprivation.The term ferredoxin degradation is used here to indicate that the ferredoxin content in the growing cells decreased more than could be accounted for by repeated cell division. Ferredoxin = holoferredoxin = protein containing iron and sulfide; apoferredoxin = protein free of iron and sulfide