Processing of Bacillus cereus 569/H beta-lactamase I in Escherichia coli and Bacillus subtilis

Biochemical characterization of beta-lactamases Bla1 and Bla2 from Bacillus anthracis

The Sterne and Ames strains of Bacillus anthracis carry chromosomal genes bla1 and bla2, which confer beta-lactam resistance when expressed in Escherichia coli. MIC measurements and steady-state kinetic analyses indicate that Bla1 possesses penicillinase activity while Bla2 possesses penicillinase, cephalosporinase, and carbapenem-hydrolyzing activities.

Terminal truncations in amp C beta-lactamase from a clinical isolate of Pseudomonas aeruginosa

AmpC beta-lactamases from strains of Pseudomonas aeruginosa have previously been shown to be heterogeneous with respect to their isoelectric point (pI). In order to elucidate the origin of this heterogeneity enzymes were isolated from a clinical isolate of a multiresistant P. aeruginosa strain and biochemically characterized. The purification was accomplished in four chromatographic steps comprising dye-affinity, size-exclusion, hydrophobic interaction chromatography, and chromatofocusing; this resulted in five forms with pI values of 9.1, 8.7, 8.3, 8.2, and 7.6. When analysed by SDS/PAGE and agarose IEF each separated beta-lactamase appeared to be both size- and charge-homogeneous. The specific activities of the variants were very similar. MS of each isolated beta-lactamase form showed minor differences in molecular mass (range 40.0-40.8 kDa). MS of the beta-lactamase with a pI of 8.2 demonstrated the presence of two subforms. The N-terminal sequences of three of the beta-lactamases were identical to the published sequence [Lodge, J.M. , Minchin, S.D., Piddock, L.J.V. & Busby, J.W. (1990) Biochem. J. 272, 627-631], while two variants were truncated by two amino-acid residues, one of which was acidic. The previously published sequence contains an alanine as the ultimate residue, but two of the beta-lactamases showed a substitution of Ala371 for arginine, whereas in the remaining forms C-terminal truncations by one and three residues were found. Our results indicate that the P. aeruginosa strain does not harbour multiple copies of the ampC gene, but rather that the five beta-lactamase isoforms are products of a single structural gene. The combinations of the identified N- and/or C-terminal truncations explained the multiple pI values of the beta-lactamase isoforms.

The two-component lysis system of Staphylococcus aureus bacteriophage Twort: a large TTG-start holin and an associated amidase endolysin

The lysis genes of the virulent Staphylococcus aureus bacteriophage Twort were cloned and their nucleotide sequences determined. The endolysin gene plyTW encodes a 53.3-kDa protein, whose catalytic site is located in the amino-terminal domain. An enzymatically active fragment (N-terminal 271 amino acids) was overexpressed in Escherichia coli and partially purified. The enzyme rapidly cleaves staphylococcal peptidoglycan, and was shown to act as N-acetylmuramoyl-L-alanine amidase (EC 3.5.1.28). Significant sequence homology to the specific cell wall targeting domain of lysostaphin was observed in a 101-amino acid C-terminal overlap. However, we found that the large C-terminal portion (63%, 295 aa) of PlyTW is not required for staphylolytic activity. Located upstream of and overlapping plyTW by 35 bp in a different reading frame (+1), we identified holTW, which starts with a single TTG triplet. The gene specifies a 185-amino acid (20.5 kDa) holin protein, which features two potential hydrophobic, antiparallel transmembrane domains, and a highly charged, acidic C-terminus. HolTW is the largest class II holin described to date. It can substitute for the defective allele in phase lambda S' amber mutants, both in trans from an expression plasmid, and from within gt11::holTW. The proposed function is the formation of unspecific membrane lesions to promote access of the endolysin to the bacterial peptidoglycan.

Cloning and sequencing of a beta-lactamase-encoding gene from the insect pathogen Bacillus thuringiensis

A beta-lactamase (Bla)-encoding gene (bla) from Bacillus thuringiensis (Bt) was cloned and the nucleotide (nt) sequence was determined. Both the nt sequence and deduced amino acid sequences reveal that the Bt Bla is very similar to that of B. cereus and other group A Bla. The transcription start point was also determined. Comparison of the upstream region of Bt bla with that of other genes suggested the presence of three sequence elements that might be involved in promoter function: the -10 (TCGGTGAT) and -35 (TTAT) sequences, an A+T-rich region (5'TACTAGCTATAATTTTTTAGT) and an inverted repeat sequence (5'-GAGATAGAGGC[GCTACTATCTC).

Sequence, expression, and function of the gene for the nonphosphorylating, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase of Streptococcus mutans

We report the sequencing of a 2,019-bp region of the Streptococcus mutans NG5 genome which contains a 1,428-bp open reading frame (ORF) whose putative translation product had 50% identity to the amino acid sequences of the nonphosphorylating, NADP-dependent glyceraldehyde-3-phosphate dehydrogenases (GAPN) from maize and pea. This ORF is located approximately 200 bp downstream of the ptsI gene coding for enzyme I of the phosphoenolpyruvate:sugar phosphotransferase transport system. Mutant BCH150, in which the putative gapN gene had been inactivated, lacked GAPN activity that was present in the wild-type strain, thus positively identifying the ORF as the S. mutans gapN gene. Another strain of S. mutans, DC10, which contains an insertionally inactivated ptsI gene, still possessed GAPN activity, as did S. salivarius ATCC 25975, which contains an insertion element between the ptsI and gapN genes. Since the wild-type S. mutans NG5 lacks both glucose-6-phosphate dehydrogenase and NADH:NADP oxidoreductase activities, the NADP-dependent glyceraldehyde-3-phosphate dehydrogenase is important as a means of generating NADPH for biosynthetic reactions.

Lactobacillus plantarum ldhL gene: overexpression and deletion

Lactobacillus plantarum is a lactic acid bacterium that converts pyruvate to L-(+)- and D-(-)-lactate with stereospecific enzymes designated L-(+)- and D-(-)-lactate dehydrogenase (LDH), respectively. A gene (designated ldhL) that encodes L-(+)-lactate dehydrogenase from L. plantarum DG301 was cloned by complementation in Escherichia coli. The nucleotide sequence of the ldhL gene predicted a protein of 320 amino acids closely related to that of Lactobacillus pentosus. A multicopy plasmid bearing the ldhL gene without modification of its expression signals was introduced in L. plantarum. L-LDH activity was increased up to 13-fold through this gene dosage effect. However, this change had hardly any effect on the production of L-(+)- and D-(-)-lactate. A stable chromosomal deletion in the ldhL gene was then constructed in L. plantarum by a two-step homologous recombination process. Inactivation of the gene resulted in the absence of L-LDH activity and in exclusive production of the D isomer of lactate. However, the global concentration of lactate in the culture supernatant remained unchanged.

An efficient expression and secretion system based on Bacillus subtilis phage phi 105 and its use for the production of B. cereus beta-lactamase I

A novel expression system based on the Bacillus subtilis bacteriophage phi 105 has been developed to permit the high-level synthesis and secretion of beta-lactamase I (BlaI) from Bacillus cereus. Shotgun insertion of a promoterless lacZ gene into the phage genome permitted the identification of a clone producing large amounts of beta-galactosidase (beta Gal), indicating the transcription of the reporter gene from a strong phage promoter. The insertion also blocked lysis of the host cell. Although the insertion in the original prophage was complex, plasmid vectors and prophage derivatives have been developed to facilitate the replacement of lacZ with other genes for expression. The new prophages contain two additional mutations: an ind mutation, which greatly enhances the normally poor transformability of phi 105 lysogens, and a cts mutation, which allows thermo-induction of phage development and protein production. Induction of a derivative prophage containing the blaI gene from B. cereus resulted in the production of up to 500 micrograms of secreted BlaI per ml of culture supernatant.

A novel Bacillus subtilis expression vector based on bacteriophage phi 105

We have developed a novel expression vector based on the bacteriophage phi 105, and employed it for the production of mutant beta-lactamases in Bacillus subtilis. Expression of the beta-lactamase-encoding gene was low when cloned into the prophage under the control of its own promoter. However, expression was considerably elevated when the gene was inserted into the phage genome in the same orientation as phage transcription. A defective phi 105 vector was constructed with a deletion removing a region needed for cell lysis, and with a mutation in the immunity repressor, rendering it temperature sensitive. Production of beta-lactamase could then be induced by a shift in temperature and without concomitant cell lysis, facilitating purification of the protein from the culture supernatant. This phage has considerable potential for development as a vector for controllable production of heterologous proteins in B. subtilis.

Cloning and nucleotide sequence of the gene coding for enzymatically active fragments of the Bacillus polymyxa beta-amylase

The gene encoding beta-amylase was cloned from Bacillus polymyxa 72 into Escherichia coli HB101 by inserting HindIII-generated DNA fragments into the HindIII site of pBR322. The 4.8-kilobase insert was shown to direct the synthesis of beta-amylase. A 1.8-kilobase AccI-AccI fragment of the donor strain DNA was sufficient for the beta-amylase synthesis. Homologous DNA was found by Southern blot analysis to be present only in B. polymyxa 72 and not in other bacteria such as E. coli or B. subtilis. B. polymyxa, as well as E. coli harboring the cloned DNA, was found to produce enzymatically active fragments of beta-amylases (70,000, 56,000, or 58,000, and 42,000 daltons), which were detected in situ by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Nucleotide sequence analysis of the cloned 3.1-kilobase DNA revealed that it contains one open reading frame of 2,808 nucleotides without a translational stop codon. The deduced amino acid sequence for these 2,808 nucleotides encoding a secretory precursor of the beta-amylase protein is 936 amino acids including a signal peptide of 33 or 35 residues at its amino-terminal end. The existence of a beta-amylase of larger than 100,000 daltons, which was predicted on the basis of the results of nucleotide sequence analysis of the gene, was confirmed by examining culture supernatants after various cultivation periods. It existed only transiently during cultivation, but the multiform beta-amylases described above existed for a long time. The large beta-amylase (approximately 160,000 daltons) existed for longer in the presence of a protease inhibitor such as chymostatin, suggesting that proteolytic cleavage is the cause of the formation of multiform beta-amylases.

Cloning and characterization of the 5' region of the cell wall protein gene operon in Bacillus brevis 47

Bacillus brevis 47 secretes vast amounts of proteins derived from both middle wall protein (MWP) and outer wall protein into the medium. The 5' region of the cell wall protein gene operon was cloned into Bacillus subtilis and subsequently into B. brevis 47. On the basis of the nucleotide sequence analysis, an open reading frame coding for MWP was identified on the cloned DNA fragment. Two potential translation initiation sites for the MWP gene are located tandemly in the same reading frame. Each of the sites contains a sequence highly homologous to the 3' end of B. brevis rRNA and an initiation codon. The translational fusion of the 5' region of the MWP gene with the Bacillus licheniformis alpha-amylase gene resulted in the efficient expression of the alpha-amylase gene in B. brevis 47. Of the two potential translation initiation sites, the one located upstream could be eliminated without affecting the expression of the MWP-alpha-amylase fusion gene, suggesting that MWP is synthesized in a precursor form with a signal peptide of 23 amino acid residues. S1 nuclease mapping of the cell wall protein gene transcripts suggested the possibility of the existence of several promoters in the 5' region within 300 base pairs from the translation initiation sites; one promoter was definitely localized within this part of the 5' region, and it was capable of expressing a heterologous gene fusion at a high level. The roles of the apparent structural complexity of the 5' region of the cell wall protein gene operon are discussed in connection with the efficient gene expression.

Cloning and sequencing of the blaZ gene encoding beta-lactamase III, a lipoprotein of Bacillus cereus 569/H

It has not been clear whether the membrane-bound beta-lactamase III of Bacillus cereus 569 is a separate enzyme or a modified form of the secreted beta-lactamase I. The membrane enzyme is an acyl-glyceride thioether-linked lipoprotein (J. B. K. Nielsen and J. O. Lampen, Biochemistry 22:4652-4656, 1983) and thus is probably a separate entity. We cloned the beta-lactamase III gene (blaZ) on a 4.9-kilobase-pair ClaI fragment from mutant strain 569/H (constitutive for high-level production of beta-lactamases I, II, and III), and the nucleotide sequence was determined. The structural gene was flanked by typical promoter, transcription termination, and translation initiation sequences. Expression of the cloned gene in Escherichia coli was low in exponential-phase cultures and increased only as the cultures reached the stationary phase. The deduced amino acid sequence indicates a pre-beta-lactamase III of 316 amino acid residues (35,021 daltons), with a 29-residue signal peptide and a mature lipoprotein form of approximately 32,500 daltons. The 12 NH2-terminal residues of a 21-kilodalton tryptic peptide from the B. cereus membrane enzyme were in agreement with the sequence deduced from the cloned gene. The amino acid sequence was highly homologous to the class A beta-lactamases, especially that of Bacillus licheniformis 749. beta-Lactamase III is a distinct class A enzyme and the product of a separate gene (blaZ).

Genetic and molecular analyses of Escherichia coli N-acetylneuraminate lyase gene

Two plasmids containing the N-acetylneuraminate lyase (NALase) gene (nanA) of Escherichia coli, pNL1 and pNL4, were constructed. Immunoprecipitation analysis indicated that the 35,000-dalton protein encoded in pNL4 was NALase. The synthesis of NALase in E. coli carrying these plasmids was constitutive.

Efficient synthesis and secretion of a thermophilic alpha-amylase by protein-producing Bacillus brevis 47 carrying the Bacillus stearothermophilus amylase gene

Bacillus subtilis and Bacillus brevis 47-5, carrying the Bacillus stearothermophilus alpha-amylase gene on pUB110 (pBAM101), synthesized the same alpha-amylase as the donor strain as determined by the enzyme's thermal stability and NH2-terminal amino acid sequence. Regardless of the host, the 34-amino acid signal peptide of the enzyme was processed at exactly the same site between two alanine residues. B. brevis 47-5(pBAM101) secreted the enzyme most efficiently of the hosts examined, 100, 15, and 5 times more than B. stearothermophilus, Escherichia coli HB101(pH1301), and B. subtilis 1A289(pBAM101), respectively. The efficient secretion of the enzyme in B. brevis 47-5(pBAM101) was suggested to be due to the unique properties of the cell wall of this organism.

Cloning and sequencing of the metallothioprotein beta-lactamase II gene of Bacillus cereus 569/H in Escherichia coli

The structural gene for beta-lactamase II (EC 3.5.2.6), a metallothioenzyme, from Bacillus cereus 569/H (constitutive for high production of the enzyme) was cloned in Escherichia coli, and the nucleotide sequence was determined. This is the first class B beta-lactamase whose primary structure has been reported. The amino acid sequence of the exoenzyme form, deduced from the DNA, indicates that beta-lactamase II, like other secreted proteins, is synthesized as a precursor with a 30-amino acid N-terminal signal peptide. The pre-beta-lactamase II (Mr, 28,060) is processed in E. coli and in B. cereus to a single mature protein (Mr, 24,932) which is totally secreted by B. cereus but in E. coli remains intracellular, probably in the periplasm. The expression of the gene in E. coli RR1 on the multicopy plasmid pRWHO12 was comparable to that in B. cereus, where it is presumably present as a single copy. The three histidine residues that are involved (along with the sole cysteine of the mature protein) in Zn(II) binding and hence in enzymatic activity against beta-lactams were identified. These findings will help to define the secondary structure, mechanism of action, and evolutionary lineage of B. cereus beta-lactamase II and other class B beta-lactamases.

Cloning and sequencing of the beta-lactamase I gene of Bacillus cereus 5/B and its expression in Bacillus subtilis

The beta-lactamases of Bacillus cereus have attracted interest because they are secreted efficiently, because multiple enzymes are frequently present, and because their regulation has unusual features. beta-Lactamase I of strain 5/B is produced constitutively at a high level, and the exoenzyme appears to be several thousand daltons larger than the corresponding product of strain 569/H. We have cloned the gene for 5/B beta-lactamase I in Escherichia coli and B. subtilis and have sequenced the structural portion and the regulatory regions. The 5/B enzyme is produced at a low level in E. coli RR1(pRWY200) and remains cellbound. In B. subtilis it is formed in large amounts, and over 90% of it is released into the medium. There is a large degree of homology between the promoter and leader peptide regions of the 5/B and 569/H genes; both utilize UUG as the translation initiation codon (P. S. F. Mézes, R. W. Blacher, and J. O. Lampen, (J. Biol. Chem. 260:1218-1223, 1985). Although there are significant differences in the peptide segment where processing would be expected to occur, the NH2 terminus of the major 5/B product from B. subtilis BD170(pRWY215) is His-44, which is the same as the NH2 terminus of the major 569/H product from B. subtilis BD170(pRWM5).