Pathways of ammonia assimilation in obligate methane utilizers

NADP+-dependent glutamate dehydrogenase from the facultative methylotroph Hyphomicrobium X

“…When nitrate was the nitrogen source the GS/GOGAT pathway was utilised irrespective of the nitrogen concentration in the medium [1]. The results did not confirm data reported using obligate methylotrophs [2] and methylotrophs [3] which utilize the serine pathways for carbon assimilation and lack GDH activity under any growth conditions. In contrast a study with Pseudomonas ( Methylobacterium ) AM1 and Pseudomonas MA [4] showed that the distribution of the N-assimilatory enzymes in these organisms were similar to that of Hyphomicrobium X [1].…”

Methane-oxidizing microorganisms.

“…Shishkina and Trotsenko (147) found that M. capsulatus, used in their studies of nitrogen assimilation (see above), possessed metabolic activities typical of both type I and type II methanotrophs and suggested that the species might represent an intermediate between the two types. Further evidence to this effect is cited by Taylor et al 166, who detected the enzymes of the autotrophic Calvin cycle in M. capsulatus (Bath) as well as [1-14C]glycolate incorporation by a pathway probably involving enzymes found in the type II serine pathway for carbon assimilation.…”

NADP-dependent glutamate dehydrogenase from a facultative methylotroph, Pseudomonas sp. strain AM1

“…However, if ammonium chloride is provided as the nitrogen source with succinate as the carbon source, the organism elaborates a high level of an NADP-dependent GDH that has a pH optimum of 9.0 (4). This finding was of interest because previous studies had indicated that GDH was absent in some methylotrophs (18,25), even after growth with ammonia as the nitrogen source. Moreover, the GDH gene from Escherichia coli had been cloned into Methylophilus methylotrophus to try to increase cell yield of this organism in industrial use (27).…”

“…The fact that there are also high levels of glutaminesynthetase-glutamine:2-oxoglutarate aminotransferase present during growth of Pseudomonas sp. strain AM1 on succinate-ammonium chloride, coupled with the previous findings that other methylotrophs completely lack GDH (18,20,25,27), raised the possibility that the GDH found in Pseudomonas sp. strain AM1 was used for glutamate degradation rather than its synthesis.…”