Mutations in Escherichia coli that relieve catabolite repression of tryptophanase synthesis. Tryptophanase promoter-like mutations

L-Tryptophan represses persister formation via inhibiting bacterial motility and promoting antibiotics absorption

Aim: The bacterial persisters have emerged as a huge threat to human health. Here, we investigated the role of L-tryptophan in bacterial persister killing by aminoglycoside antibiotics (AGs). Materials & methods: The relevance to the antibiotic susceptibility of Escherichia coli including transcriptional sequencing, gene expression, intracellular ATP, Nicotinamide adenine dinucleotide (NAD/NADH), reactive oxygen species and membrane depolarization were determined. Results & conclusion: We found that exogenous L-tryptophan efficiently inhibited AGs-enabled persisters. The flagellar genes were almost significantly downregulated. Besides, the AGs uptake was obviously increased as the result of elevation in proton motive force (PMF) in response to L-tryptophan-mediated NADH production. Taken together, these data supported a novel role of L-tryptophan in eradicating AGs persisters against E. coli.

Application of the tryptophanase promoter to high expression of the tryptophan synthase gene inEscherichia coli

The application of an inducible regulation system using the tryptophanase operon promoter (TPase promoter; Ptna) was examined for its high expression of the tryptophan synthase (TS) gene in Escherichia coli. The main problem in the application of Ptna for industrial purposes is catabolite repression by glucose, since glucose is the most abundant carbon source. However, this problem could be avoided by changing glucose to an organic acid, such as succinate, fumarate, malate and acetate, in the course of cultivation after glucose initially added was completely consumed. Under these conditions, L-tryptophan was also used to induce tryptophan synthase. Thus, the specific activity of TS in E. coli strain no. 168 harbouring pBR322F-Ptna TS was increased 500-fold compared to that of the cultured host strain. About 1 mol L-tryptophan/l reaction mixture was formed from indole and L-serine at 37 degrees C for 3.5 h.

Transcription initiation at the tryptophanase promoter of Escherichia coli K-12

Restriction fragments containing the region preceding the tryptophanase structural gene, tnaA, were used as templates for in vitro transcription experiments. A transcription initiation site was detected that was dependent on the catabolite gene activator protein (CAP) plus cyclic AMP (cAMP). The mRNA produced in vitro was fingerprinted, and the nucleotide at which transcription was initiated was localized to the vicinity of two guanine residues 316 and 318 base pairs upstream of tnaA. A region exhibiting extensive difold symmetry and homology to the CAP binding site adjacent to the lactose operon promoter exists approximately 60 base pairs preceding the site of transcription initiation. Two HinfI restriction sites are located in this region. Restriction enzyme cleavage at these sites was prevented when DNA containing the promoter region was preincubated with CAP and cAMP. RNA polymerase was incapable of protecting these sites against this cleavage. CAP and cAMP addition did not protect against cleavage at a DdeI restriction site located in the -20 region of the promoter. RNA polymerase did protect against DdeI cleavage but only in the presence of CAP and cAMP. Thus, transcription initiation at the tryptophanase promoter involves cAMP-dependent, CAP-facilitated binding of RNA polymerase to the DNA.

Nucleotide sequence of the structural gene for tryptophanase of Escherichia coli K-12

The tryptophanase structural gene, tnaA, of Escherichia coli K-12 was cloned and sequenced. The size, amino acid composition, and sequence of the protein predicted from the nucleotide sequence agree with protein structure data previously acquired by others for the tryptophanase of E. coli B. Physiological data indicated that the region controlling expression of tnaA was present in the cloned segment. Sequence data suggested that a second structural gene of unknown function was located distal to tnaA and may be in the same operon. The pattern of codon usage in tnaA was intermediate between codon usage in four of the ribosomal protein structural genes and the structural genes for three of the tryptophan biosynthetic proteins.

Catabolite repression during single and multiple induction in Escherichia coli

Intracellular concentration of cAMP regulates the synthesis of enzymes sensitive to catabolite repression. The relationship between the single and multiple induction of beta-galactosidase (EC 3.2.1.23), L-tryptophanase (EC 4.1.99.1), D-serine deaminase (EC 4.2.1.14), L-asparaginase (EC 3.5.1.1) and L-malate dehydrogenase (EC 1.1.1.37) was studied and the effect of cAMP level on the induction in Escherichia coli Crookes (ATCC 8739) was investigated. A varying degree of catabolite repression was observed during induction of individual enzymes induced separately on different energy sources. The synthesis of l-tryptophanase was most sensitive, whereas l-asparaginase was not influenced at all. Exogenous cAMP was found to overcome partially the catabolite repression of beta-galactosidase and D-serine deaminase, both during single induction. The synthesis of l-malate dehydrogenase was negatively influenced by the multiple induction even in the presence of cAMP; on the other hand, the synthesis of l-tryptophanase was stimulated, independently of the level of the exogenous cAMP. Similarly, the activity of L-asparaginase slightly but significantly increased during the multiple induction of all five enzymes; here too the activity increase did not depend on exogenous cAMP.

Synthesis of tryptophanase in Escherichia coli: isolation and characterization of a structural-gene mutant and two regulatory mutants

A mutant of E. coli has been isolated that is temperature-sensitive in respect of tryptophanase. When incubated at 60 degrees C, cell-free extracts of the mutant suffer inactivation of enzyme activity much more rapidly than similar extracts of the wild type. After lysogeny with a specialized transducing phage carrying the wild-type tryptophanase gene, the mutant is able to synthesize tryptophanase that is wild-type in its response to treatment at 60 degrees C. It is concluded that the mutation lies in the structural gene for the enzyme. Two further mutants have been isolated that synthesize tryptophanase constitutively. One mutation renders synthesis of the enzyme indifferent to the presence of inducer; the other mutation allows synthesis of the enzyme in the absence of inducer at about 35% of the fully induced wild-type rate. Neither mutation alleviates catabolite repression. Genetic mapping shows that the constitutive mutations lie very close to the structural-gene mutation, on the side of the structural gene distant from bglR.

Unstable mutations that relieve catabolite repression of tryptophanase synthesis by Escherichia coli

From strains of Escherichia coli that carry deletions of the trp region, five different mutants were isolated that were capable of synthesizing tryptophanase at unusually high rates in conditions of severe catabolite repression. Notwithstanding the comparative insensitivity to catabolite repression, the rates of tryptophanase synthesis in the mutants were greatly diminished by the introduction of a defective gene for adenyl cyclase. Each of the mutants segregated variants of the parental type. The results of genetic analysis appear to be consistent with the mutants arose by duplication of the tryptophanase gene.