Regulation of Nitrogen Assimilation in Streptomycetes and Other Actinobacteria
Wolfgang Wohlleben, Yvonne Mast and Jens Reuther
from: Streptomyces: Molecular Biology and Biotechnology (Edited by: Paul Dyson). Caister Academic Press, U.K. (2011)
Streptomycetes, as most bacteria, possess two ways to assimilate ammonium: Whereas the glutamate dehydrogenase is active under high nitrogen supply, the glutamine synthetase-glutamate synthase (GS-GOGAT) pathway is required under nitrogen limiting conditions. The major GS activity is mediated by the typical prokaryotic-type GSI enzyme. A second GS activity is conveyed by the GSII enzyme, belonging to the eukaryotic-type GS. This enzyme contributes to the overall GS activity mainly under N-limitations and during stationary growth. Three further genes (glnA1, glnA2, glnA3) encoding GSI-like enzymes to which no function could yet be assigned are located in all genomes of Streptomyces sequenced so far. The activity of GSI is post-translationally regulated by an adenylyltransferase (GlnE), which modifies the enzyme in response to nitrogen availability. In contrast to enteric bacteria, the PII protein and its modifying enzyme, the adenylyltransferase GlnD, are not involved in the control of GlnE. The central transcriptional regulator GlnR which can act as activator and repressor, respectively, controls the expression of various genes involved in nitrogen supply, such as genes encoding a urease and an ammonium transporter, as well as genes of the ammonium assimilation pathways. GlnR itself can be multiply modified probably reflecting different nitrogen conditions read more ...