Strain MG 1655+hisGr hisL'-Delta, purR, which produces histidine with a weight yield of approximately 12% from glucose, was constructed through directed chromosomal modifications of the laboratory Escherichia coli strain MG 1655+, which has a known genome sequence. A feedback-resistant ATP-phosphoribosyl transferase encoded by the mutant hisGr (E271 K) was the main determinant of histidine production. A further increase in histidine production was achieved by the expression enhance of a mutant his operon containing hisGr through the deleting attenuator region (hisL'-Delta). An increase in the expression of the wildtype his operon did not result in histidine accumulation. Deletion of the transcriptional regulator gene purR increased the biomass produced and maintained the level of histidine production per cell under the fermentation conditions used.
Cryptic conjugative plasmid p19 from the environmental Bacillus subtilis strain 19 was labeled with the cat gene conferring resistance to chloramphenicol. The resulting plasmid, p19 cat , was used to estimate the transfer frequency, to study the dynamics of plasmid transfer, and to detect some specific features of conjugation between various B. subtilis strains.
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