Utilization of selected leucine peptide amides by Escherichia coli

Transport and hydrolysis of peptides by microorganisms

The structural specificities of the dipeptide and oligopeptide permeases of E. coli are briefly reviewed and related to the requirements found for other microorganisms. New, quick, sensitive methods for studying peptide transport are described, based on the following: (i) peptide-dependent incorporation of free radioactive amino acid into newly synthesized protein by a double amino acid auxotroph, (ii) colorimetric assay of peptide-dependent enzyme synthesis by an amino acid auxotroph, (iii) dansyl fingerprint technique. These approaches provide information on peptide binding affinity to a permease and rates of peptide uptake and amino acid efflux. Among current and future research areas considered are: the influence of the pKb of the N-terminal amino group on transport, generality of peptide transport in microorganisms, energy coupling and regulation, involvement of binding proteins, and the 'smugglin' concept. Peptide hydrolysis, and nutritional ultilization of peptides, by microorganisms are briefly discussed.

Effects of environmental changes on expression of the oligopeptide permease (opp) genes of Borrelia burgdorferi

We analyzed expression of a putative oligopeptide permease (Opp) of Borrelia burgdorferi. Unlike the opp operons of other bacteria for which there is a single substrate binding protein, B. burgdorferi codes for three substrate binding proteins (OppA-I to -III) in its opp operon and an additional two homologs on plasmids (OppA-IV and -V). Instead of a single promoter region regulating transcription of the entire operon, as seen in other bacterial opp operons, it appears that among oppA-I, -II, and -III, as well as oppA-IV and -V, each has a potential upstream promoter region. We tested the function of these putative promoter sequences by fusion to a promoterless beta-galactosidase reporter gene in pCB182. Each of the promoter regions was found to be active. The level of activity in the reporter constructs closely paralleled the level of expression of each gene in in vitro-grown B. burgdorferi. Changes in carbon and nitrogen availability differentially affected individual promoters, but no changes in promoter activity were seen when Escherichia coli bacteria (with the promoter constructs) were grown in various concentrations of phosphate and leucine and changes in pH. Expression of specific oppA genes with B. burgdorferi varied significantly between its mouse and fed and unfed tick hosts. Differences in regulation of opp gene expression suggest a potential role in environmental response by the organism.

Peptide utilization by oral streptococci

Streptococcus mitis ATCC 903 and Streptococcus sanguis 804 could utilize large peptides present in proteose peptone as their sole source of nitrogen but grew poorly in amino acid medium. By contrast, Streptococcus mutans BHT and S. mutans IB grew in amino acid medium but could not utilize large peptides. Streptococcus sp. strain Bravato had requirements for both peptides and amino acids. Peptide size did not seem important for the utilization of peptides by S. mitis except that dipeptides were not utilized. Large peptides were essential for depressed hyaluronidase synthesis in nongrowing S. mitis. Intracellular aminopeptidase activities were high in S. mitis ATCC 903 and Streptococcus sp. strain Bravato, intermediate in S. sanguis 804, and low in S. mutans BHT and S. mutans IB.

Hydrophobic peptide auxotrophy in Salmonella typhimurium

The growth of a pleiotropic membrane mutant of Salmonella typhimurium with modified lipopolysaccharide composition was found to be strictly dependent on the peptone component of complex media. Nutritional Shiftdown into minimal media allowed growth for three to four generations. Of 20 commercial peptones, only enzymatic digests supported growth to varying degrees. Neither trace cations, amino acids, vitamins, carbohydrates, lipids, glutathione, polyamines, carbodimides, nor synthetic peptides stimulated growth; however, cells still metabolized carbohydrates, and amino acid transport systems were shown to be functional. A tryptic digest of casein was fractionated into four electrophoretically different peptide fractions of 1,000 to 1,200 molecular weight which supported growth to varying degrees. The best of these was further fractionated to two highly hydrophopic peptides. N-terminal modifications eliminated biological activity. Fluorescein-conjugated goat antibody to rabbit immunoglobulin G was used as a probe to detect antipeptide antibody-peptide complexes on membrane preparations. Cells grown on peptone distributed the peptide into both inner and outer membranes. The peptide could be removed with chaotropic agents, and cells had to be pregrown in peptone-containing media to bind the hydrophobic peptide. The gene (hyp) responsible for peptide auxotrophy was mapped at 44 to 45 units by conjugation.