Stalk Formation and Its Inhibition in Caulobacter crescentus

Estimates of average rates of stalk formation over several generations of growth in Caulobacter crescentus showed that long-stalked Sk1 mutant and phosphate-starved wild-type cultures produce stalk material at about twice the rate of wild-type C. crescentus grown with adequate nutrients. Thus, the long stalks of Sk1 or phosphate-starved caulobacters are not merely a function of their longer doubling times. Inhibition of cell division of Sk1 418 with mitomycin C (MC) caused production of cellular filaments and resulted in inhibition of stalk formation. There was no appreciable decrease in total cell mass or in rates of ribonucleic acid and protein synthesis in the MC-treated cultures as compared with controls, but stalk formation, which is normally dependent on these processes, was severely retarded. Average stalk lengths in MC-treated Sk1 cultures were 30% of those found in control cultures. MC-produced cellular filaments were also subjected to deoxyribonucleic acid analysis and ultrastructural examination. The deoxyribonucleic acid content of MC-treated bacteria was about 50 to 60% that of untreated bacteria. Hydroxyurea also was found to produce some cellular filaments and shorter stalks, but with accompanying decreases in growth rate and yield.