Date of Award

Spring 1984

Project Type


Program or Major


Degree Name

Doctor of Philosophy


Aquaspirillum magnetotacticum strain MS-1 grew microaerobically but not anaerobically with NO(,3)('-) or NH(,4)('+) as the sole nitrogen source. Cell yields varied directly with NO(,3)('-) concentration under microaerobic conditions. Products of NO(,3)('-) reduction by growing cells included NH(,4)('+), N(,2)O, NO, and N(,2) but not NO(,2)('-) or NH(,2)OH. The inclusion of NH(,4)('+) in growth medium prevented NO(,3)('-) reduction to NH(,4)('+) but not to N(,2)O or N(,2). Cells consumed O(,2) while denitrifying and this appears to be the first described species with an absolute requirement for O(,2) while denitrifying.

Cultures grown with NO(,3)('-), in contrast to NH(,4)('+), contained fewer cells without magnetosomes. Moreover, among the cells with these intracellular magnetic particles, a higher average number per cell and a higher average cell magnetic moment was obtained with NO(,3)('-). This effect of cell nitrogen source on culture magnetism was investigated further with growing cells and cell-free extracts. The results indicated that Fe('+3) reduction by cell-free extracts of A. magnetotacticum was independent of electron transport chain components and suggested that Fe('+3) and NO(,3)('-) reduction proceeded independently in the cell.

A. magnetotacticum strain MS-1 and several non-magnetic mutants derived from it, fixed N(,2) (reduced acetylene) microaerobically but not anaerobically even with NO(,3)('-). Cells of A. magnetotacticum reduced acetylene at rates comparable to those of Azospirillum lipoferum under similar conditions but at a much lower rate than that of Azotobacter vinelandii grown aerobically.