Microbial Production of Ammonium Ion from Nitrogen
Proceedings of the National Academy of Sciences, 72 (1):
136-139 (1975)DOI: 10.1073/pnas.72.1.136
Abstract
Genetic manipulation of nitrogenase and key glutamate-forming enzymes can provide mutants that excrete fixed N2 as NH4+. A derepressed N2 fixation mutant (SK-24) has been isolated, which excretes up to 20.2 micro mol of fixed N2 as NH4+ per mg of cell protein in 24 hr at room temperature. Biochemical analysis shows that this mutant, which requires glutamate for growth, releases fixed N2 as NH4+ into the environment because of (i) constitutive synthesis of nitrogenase and (ii) genetic blocks resulting in losses of glutamate synthase L-glutamine:2-oxoglutarate aminotransferase (NADPH oxidizing), EC 2.6.1.53 and glutamate dehydrogenase L-glutamate:NADP oxidoreductase (deaminating), EC 1.4.1.4 activities, enzymes essential for NH4+ assimilation into cell material. The parent strain (asm-1), missing only glutamate synthase activity, also actively excretes NH4+ during early phases of its growth but eventually reutilizes the NH4+. A maximum yield of 4.0 micro mol of NH4+/ml per 24 hr has been noted for asm-1 only during the growth period. Biosynthesis of NH4+ proceeds at the expense of a variety of fermentable sugars, such as sucrose or glucose, with a maximum energy conversion efficiency of about 5 glucose degraded per NH4+ formed. The use of microbes for production of NH4+ fertilizer is discussed.
Description
Microbial Production of Ammonium Ion from Nitrogen -- Shanmugam and Valentine 72 (1): 136 -- Proceedings of the National Academy of Sciences