Published by Elsevier FEM 02757 Respiratory oscillations in synchronised Paracoccus denitrificans

Paracoccus denitrificans was synchronised by a selection method, and factors affecting respiratory activity during the cell cycle were investigated. Oxygen uptake rates increased iscontinuously in 2 steps, with mid-points of rises centred at around 0.3 and 0.8 of a cycle. Addition of KCN (0.1 mM) resulted in a constant level of inhibition of respi-ration (approx. 70%) irrespective of cell age. How-ever, the addition of a respiratory uncoupler stimulated oxygen uptake rates in a cell-cycle de-pendent manner. Maxima of stimulation occurred at points intermediate to the rises in respiratory activity and were centred at around 0.18 and 0.55 of the cell cycle. with a more recent version in which the chain is regarded as a series of complexes [5]. However, to our knowledge, little is known regarding the func-tioning of the chain during the cell cycle. Previous work on respiratory activity during bacterial cell cycles has suggested discontinuous activities in Alcaligenes eutrophus [6,7], Bacillus subtilis [8,9] and Escherichia coli [10]. Other investigations of the latter organism have also shown continuous increases in respiratory activity, cytochrome o, other cytochromes and iron-sulphur clusters [11,12]. Reasons for these different results in E. coli are unknown, but may include the nature of the carbon source for growth or the different methods used to prepare synchronous cultures. 2