STUDIES OF THE IRON-SULFUR CENTERS OF THE BACTERIA SHEWANELLA-PUTREFACIENS (MR-1)

Shewanella putrefaciens (MR-1) can be grown using any one of sevaral d ifferent terminal acceptors. This respiratory versatility stimulated o ur studies of the respiratory chain of MR-1 using whole cell analysis by ESR spectroscopy. Initial analyses of aerobically grown cells showe d the presence of the succinate dehydrogenase complex. Also, it was sh own that in S. putrefaciens which were grown anaerobically with iron a s the only electron acceptor the ESR signal at g = 2.021 appeared at l ow temperatures. This ESR signal resembled the ESR signal of [Fe-S] ce nter of succinate dehydrogenase in oxidized state. However this new ES R signal had a different temperature dependence. It can be seen at tem perature as high as 40 K. The line shape and g-factor of the new cente r are very similar to those of [3Fe-4S] centers. As this ESR signal ca n be seen only in the anaerobic samples grown with iron as acceptor we suggest that this center is located in the terminal part of the respi ratory chain and is associated with the reduction of iron or another e lectron acceptor.