ISSN:
1432-072X
Keywords:
Rhizobium leguminosarum
;
Nitrogenase
;
Acetylene reduction
;
Growth yields
;
Chemostat
;
Fedbatch
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Rhizobium leguminosarum is capable of nitrogen fixation in free living cultures. Nitrogenase activity can be induced when the ammonia supply of a nitrogen-limited culture, in which the oxygen concentration is regulated at 1 μm, is switched off. Assuming a nitrogen content of the cell of 12% the theoretical washout curve of such a culture can be calculated. The measured optical densities are higher than the calculated ones. In one case, 8 days after the shift, the medium supply was switched off and batch growth with molecular nitrogen occurred. Acetylene reduction started immediately in samples taken 2 days after the shift. Addition of ammonium chloride to the test vials inhibited acetylene reduction. The highest specific activities were found 5–8 days after the shift (100 nmol ethylene formed per milligram dry weight per hour). From this activity a μmax of 0.007–0.009 (generation time 76–98 h) on molecular nitrogen can be calculated. After the shift Y mannitol decreased from 33 to 23 in the first 48 h. Three days after the shift Y mannitol had a value of 15. During batch growth Y mannitol had a value of 8. In a carbon-limited fed-batch culture R. leguminosarum shows three distinct growth phases with different values of Y mannitol. This is an indication for a stringent response in the third growth phase, and probably nitrogen fixation occurs under stringent response situations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00414480
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