RT Journal Article SR Electronic(1) A1 Dalton, H. A1 Postgate, J. R.YR 1969 T1 Growth and Physiology of Azotobacter chroococcum in Continuous Culture JF Microbiology, VO 56 IS 3 SP 307 OP 319 DO https://doi.org/10.1099/00221287-56-3-307 PB Microbiology Society, SN 1465-2080, AB SUMMARY Azotobacter chroococcum (ncib 8003) organisms, grown in continuous culture without fixed nitrogen, had chemical compositions at various dilution rates characteristic of nitrogen-limited populations. Fast-growing variants were selected for at high dilution rates; the efficiency of nitrogen fixation decreased with decreasing growth rate. In suitable media, carbon- and phosphate-limited populations were obtained and showed different compositions; they were very sensitive to inhibition by oxygen. Carbon-limited populations utilizing NH4 under argon were not oxygen sensitive; they formed nitrogenase when they were N-limited. The chemical compositions of the various populations corresponded to theory for the nutritional state considered. Nitrogen fixation entrained a maintenance coefficient of 1·06 g. substrate/g. organism/hr compared with about 0·40 for ammonia assimilation. Assuming most of this maintenance was directed to respiratory protection of nitrogenase, an extrapolated maximum requirement of 4 moles ATP/mole N2 fixed was observed. Attempts to repeat reports of (1) dependence of cytochrome pattern on nitrogen fixation and (2) increased efficiency of fixation with ultraviolet-irradiated N2 were not successful with the strain of A. chroococcum used., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-56-3-307