ISSN:
1432-072X
Keywords:
Ammonia assimilation
;
In vivo 15N and 31P NMR spectroscopy
;
Amino acid metabolism
;
Carbon limitation
;
Cyanobacterium
;
Microcystis firma
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Cultures of the cyanobacterium Microcystis firma show rhythmic uptake and release of ammonia under conditions of carbon limitation. The massive removal of ammonia from the medium during the first light phase has little impact on the intracellular pH: a pH shift of less than 0.2 U towards the alkaline can be measured by in vivo 31P NMR. Furthermore, the energy status of the cells remains regulated. In vivo 15N NMR of M. firma, cultivated either with labelled nitrate or ammonia as the sole nitrogen source, reveals only gradual differences in the pool of free amino acids. Additionally both cultivation types show γ-aminobutyric acid, acid amides and yet unassigned secondary metabolites as nitrogen storing compounds. Investigating the incorporation of nitrogen under carbon limitation, however, only the amide nitrogen of glutamine is found permanently labelled in situ. While transamination reactions are blocked, nitrate reduction to ammonia can still proceed. Cation exchange processes in the cell wall are considered regarding the ammonia disappearance in the first phase, and the control of ammonia uptake is discussed with respect to the avoidance of intracellular toxification.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00245394
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