ROLE OF MENAQUINONE IN THE REDUCTION OF FUMARATE, NITRATE, IRON(III) AND MANGANESE(IV) BY SHEWANELLA-PUTREFACIENS MR-1

Mutants of Shewanella putrefaciens MR-1 deficient in menaquinone and m ethylmenaquinone, but which have wild-type levels of ubiquinone, retai n the ability to use trimethylamine N-oxide as an electron acceptor, b ut they lose the ability to use nitrate, iron(III), and fumarate as el ectron acceptors. These mutants also show a reduced rate of manganese( IV) reduction. One of these mutants could be restored to essentially w ild-type phenotype by supplementing the medium with 1,4-dihydroxy-2-na phthoic acid. A requirement for naphthoquinones in iron(III) reduction and a preference for naphthoquinones in manganese(IV) reduction provi de further support that the metal reducing systems in MR-1 are linked to anaerobic respiration.