SUMMARY

Synchronous cultures of Alcaligenes eutrophus (Hydrogenomonas eutropha HI 6) were prepared by a size selection method which gave high synchrony indices (0.70 to 0.85). Unlike the smooth exponential increase which was observed in exponentially growing cultures, the respiration rate kg-atom 0 min-l (ml culture)-l] of synchronous cultures exhibited a periodic increase which was com-posed of two ‘steps ’ with rises centred at approximately 0.4 and 0.9 of the cell-cycle. The respiration of exponentially growing and synchronous cultures was stimulated by the uncoupling agent carbonyl cyanide m-chlorophenylhydrazone; the degree of stimulation varied during the cell-cycle and was inversely related to the respiration rate. The observed discontinuous patterns of respiration are dis-cussed with reference to the reported respiratory properties of other micro-organisms in synchronous cultures