Ammonium excretion by a mutant of the nitrogen-fixing cyanobacterium Anabaena siamensis
✍ Scribed by Selwin P. Thomas; Arieh Zaritsky; Sammy Boussiba
- Publisher
- Elsevier Science
- Year
- 1991
- Tongue
- English
- Weight
- 508 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0960-8524
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✦ Synopsis
Anabaena siamensis isolated from rice fields in "lhailand is a fast growing cyanobacterium with a high nitrogen-fixing activity. Mutant strains resistant to the L-glutamate analogue, t.-methionine sulfoximine (MSX) were isolated by ethyl methanesulfonate mutagenesis. A stable mutant named A. siamensis SS1, which released ammonium to the medium, was studied further. In batch cultures the rate of ammonium production peaked at the early log phase and gradually decreased until the 4th day (~f growth wizen the cultures reached a density of 90 l~ g chl ml-~. To obtain constant release of ammonium by SS1, continuous culture experiments were performed at a cell density of 5 lug chl ml-i and the following results were obtained." (1) growth rate as the parent (/u ." 0"123 h-1) in the presence and absence 0.[500/~M MSX," (2) 48% GS transferase activity when compared with the parent," (3) ammonium excretion at a rate of 8/z tool (rag chl)-1 h-l as measured up to 20 generations (120 h); (4) derepressed nitrogenase activity; and (5) 30% higher nitrogenase activity than that of the parent. SS1 immobilized in alginate beads (5 ktg chl ml-1) exhibited values of glutarnine synthetase and nitrogenase activity similar to those of free cells. ttowever, ammonium excretion at the rate of 11"61 /~ mol Ong chl) -1 h-l was obtained only up to 20 h ,~fier loading in bioreactors, due to the fast growth of SS l as also occurred in batch cultures.