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Applied and Environmental Microbiology, May 2003, p. 2512-2520, Vol. 69, No. 5
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.5.2512-2520.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Faculté d'Oenologie, Université de Bordeaux II, 33405 Talence Cedex, France
Received 30 July 2002/ Accepted 25 January 2003
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ftsH E. coli strain AR3291 (W3110 zad220::Tn10 sfhC21
ftsH3::kan) (20) was used to study O. oeni FtsH protein function. The E. coli strains used were grown in Luria-Bertani (LB) medium supplemented with appropriate antibiotics at the following concentrations when necessary: ampicillin, 50 µg/ml; chloramphenicol, 10 µg/ml; and kanamycin, 50 µg/ml. |
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FIG. 1. Restriction mapping of the O. oeni ftsH gene. (A) Southern blots were hybridized with either the ftsH probe (left and middle panels) or probe 2 (right panel). The O. oeni genomic DNA was digested with the following enzymes: lane 1, EcoRI; lane 2, BamHI; lane 3, HindIII; lane 4, EcoRI and BamHI; lane 5, EcoRI and HindIII; lanes 6, SalI; lanes 7, EcoRV; lanes 8, EcoRI and SalI. Lanes M, molecular size markers (in base pairs). (B) Physical map of the O. oeni ftsH gene. Restriction enzyme sites: EI, EcoRI; EV, EcoRV; H, HindIII; S, SalI. The location of the ftsH probe is indicated by a grey box above the ftsH gene; the location of probe 2 is indicated by a hatched box below the ftsH gene. Distances between restriction sites are indicated.
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Next, the complete O. oeni ftsH gene was cloned in pCR-XL-TOPO to take advantage of the ability to express the FtsH protein through the control of the lac promoter. PCR was carried out with the FTSH3 (5'-GTTAACCCCGATAATTTATTCATAATG-3') and FTSH4 (5'-GCGACCAGCTAAAGTCGCGTTTTG-3') primers. PCR was performed with 200 ng of genomic O. oeni DNA in a final volume of 100 µl with a 1 µM concentration of each primer, a 0.2 mM concentration of each of the four dNTPs, and 1.5 µl of Expand enzyme in the appropriate commercial buffer. The PCR program used consisted of 39 cycles of 1 min at 94°C, 1 min at 50°C, and 1.5 min at 72°C, followed by 10 min at 72°C. The FTSH3 primer encompasses the region from position -61 to -35 of the ftsH promoter sequence. This oligonucleotide therefore allowed cloning of the O. oeni ftsH gene with its own promoter and ribosome binding site. The FTSH4 primer represents the region from position +2229 to +2206 of the ftsH gene. Thus, its 5' extremity ends 81 nucleotides after the ftsH stop codon. A 2,290-bp fragment was amplified, purified, and cloned in pCR-XL-TOPO to yield pJPB65. We expected to find a 50:50 distribution in the orientation of inserted fragments. However, none of the 24 positive recombinant clones that were tested contained the cloned ftsH gene in the correct orientation (under the control of the lac promoter), and all contained the ftsH gene in the incorrect orientation. This is compatible with a lac promoter-monitored toxic level of ftsH gene expression (even under noninduced conditions) and is in keeping with the observation that overproduction of the H. pylori ftsH gene considerably reduced the growth rate of E. coli host cells (5). Nevertheless, the plasmid pJPB65, containing the ftsH gene in the opposite orientation with respect to the lac promoter, allowed the study of the FtsH protein function. In this construct the ftsH gene is not expressed under its own promoter and benefits only from its own ribosome binding site. Despite this, a low level of ftsH expression was possible, as observed by reverse transcription-PCR (RT-PCR) (data not shown).
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ftsH E. coli strain AR3291 transformed with either pBAD18-Cm (control plasmid) or pRJ5188 (harboring the B. japonicum ftsH gene) were grown in LB medium supplemented with chloramphenicol. They were diluted to an optical density at 600 nm of 0.1 into fresh LB medium, supplemented with antibiotic and containing 0.1% arabinose instead of glucose to induce FtsH biosynthesis through the arabinose PBAD promoter (6), and grown for 2 h at 37°C. Next, 20 µl of cell cultures was added to 180 µl of LB medium devoid of antibiotic but containing 0.1% arabinose and supplemented with various concentrations of wine (0, 20, and 25%, making 0, 2.4, and 3% ethanol, respectively). Cultures were incubated for 3 h at 25°C. Serial 10-fold dilutions were then plated on solid LB medium, and colonies were counted on the following day. Survival ratios of CFU observed in the presence of wine to those observed without wine were calculated.
Overnight cultures at 25°C of the
ftsH E. coli strain AR3291 transformed with either pCR-XL-TOPO (control plasmid) or pJPB65 (harboring the O. oeni ftsH gene) were grown in LB medium supplemented with kanamycin. They were diluted to an optical density at 600 nm of 0.1 into fresh LB medium, supplemented with antibiotic and containing glucose, and grown for 2 h at 37°C. Resistance assays were then carried out as described above, except that the LB medium contained glucose instead of arabinose during the wine shock.
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The O. oeni ftsH gene is made of an open reading frame of 2,145 bp and encodes a polypeptide of 715 amino acids with a calculated molecular mass of 75 kDa. Comparison of O. oeni FtsH protein with members of the AAA protein family revealed a high sequence identity within an ATPase module of around 200 amino acids (2). Among these AAA proteins, the O. oeni FtsH protein displayed the highest overall sequence similarity to the bacterial FtsH proteins, most notably the L. lactis homologue (Fig. 2). The O. oeni and L. lactis FtsH proteins share 59% identical residues (as given by the Clustal program), and O. oeni FtsH exhibits 52% identity to E. coli FtsH and 51% identity to B. japonicum FtsH (Fig. 2).
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FIG. 2. Comparison of the amino acid sequences of FtsH proteins from O. oeni, L. lactis, B. japonicum, and E. coli. The first residue in each row is numbered. A asterisk above the sequences indicates a perfect consensus between the four protein sequences. A cross indicates three matching residues among the four sequences. The predicted transmembrane -helices of FtsH proteins are underlined. The Walker A and B motifs are indicated. The SRH motif is indicated and appears in boldface. The boxed HEAGH domain is the zinc binding motif. Dashes indicate gaps introduced to optimize the alignment.
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-helical transmembrane segments (residues 12 to 31 and 134 to 157). The cytoplasmic domain carried the ATP binding motifs (Walker A and B motifs), the conserved region of the AAA protein family, and the putative zinc binding site (Fig. 2).
The O. oeni ftsH gene is a stress-responsive gene.
The influence of typical wine stresses upon O. oeni ftsH gene expression was tested. We did not observe any significant changes in ftsH expression when O. oeni was subjected to alcohol, sulfite, or ethidium bromide addition. In contrast, increased ftsH gene expression was observed at high temperatures and under osmotic shock (Fig. 3).
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FIG. 3. The O. oeni ftsH gene is a stress-responsive gene. The induction of O. oeni ftsH gene expression after heat or osmotic shocks was analyzed by RT-PCR. The RT-PCR patterns were obtained with cDNA from the RNA of O. oeni IOEB 8406 extracted after 3 h of application of the indicated thermal or osmotic stress. The gene-specific primers that were used are indicated on the bottoms of the panels.
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ftsH E. coli strain AR3291. This strain is a viable
ftsH mutant, due to a suppressor mutation in sfhC (fabZ) that allows cells to survive although showing slowed growth at 37°C (20). The same strain had been used to study the function of B. japonicum FtsH (15). When E. coli AR3291/pCR-XL-TOPO was grown at 37°C, it showed a clear growth defect, whereas the expression of O. oeni FtsH significantly improved the growth of E. coli AR3291/pJPB65 at 37°C (Fig. 4). Thus, O. oeni FtsH is able to confer a growth advantage upon the E. coli ftsH mutant, indicating that the heterologous protein can compensate for the loss of at least some of the important FtsH functions in E. coli AR3291.
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FIG. 4. Growth complementation of an E. coli ftsH mutant by the O. oeni ftsH gene. The E. coli ftsH strain AR3291 transformed with pCR-XL-TOPO (diamonds) or with pJPB65 (squares) was grown in LB medium at either 25°C (open symbols) or 37°C (closed symbols). OD600, optical density at 600 nm.
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ftsH cells harboring pJPB65 (O. oeni ftsH) or vector without ftsH (pCR-XL-TOPO) were exposed to wine in liquid medium, it was readily apparent that O. oeni FtsH confers resistance to this toxic medium (Fig. 5). The survival ratios were significantly higher when cells cultured with wine harbored the O. oeni and B. japonicum ftsH expression plasmids. The expression of O. oeni ftsH resulted in a 10- to 100-fold relative resistance, and that of B. japonicum ftsH resulted in a 100- to 10,000-fold relative resistance. We define relative resistance as the ratio of the survival rate of the bacteria transformed with O. oeni or B. japonicum ftsH to that of the bacteria transformed with the corresponding vectors in a given environmental condition.
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FIG. 5. The O. oeni and B. japonicum ftsH genes protect E. coli from wine toxicity. The E. coli ftsH strain AR3291 was transformed with control plasmids (pCR-XL-TOPO [A] or pBAD18-Cm [B]) (light-gray bars) and O. oeni or B. japonicum ftsH gene-containing plasmids (pJPB65 [A] and pRJ5188 [B], respectively) (dark-gray bars). After 3 h of incubation at 25°C with the indicated concentrations of wine, the bacterial cultures were serially diluted and plated. Colonies were counted, and the survival ratios (ratios of CFU observed at a given concentration of wine to those observed without added toxic compounds) were calculated.
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FIG. 6. ftsH homologues in other wine lactic acid bacteria. Southern hybridization of the ftsH probe to chromosomal DNAs from various bacteria is shown. The genomic DNAs were digested before transfer with either the EcoRI (lanes E) or HindIII (lanes H) enzymes. Lanes M, molecular size markers (in kilobase pairs). Lanes: 1, Lactobacillus fructivorans ATCC 8288; 2, P. pentosaceus ATCC 33326; 3, P. dextrinicus ATCC 33087; 4, Lactobacillus plantarum IOEB 9106; 5, P. parvulus ATCC 19371; 6, Lactobacillus buchneri ATCC 11305; 7, P. damnosus ATCC 25248; 8, Lactobacillus hilgardii IOEB 9101; 9, Lactobacillus brevis ATCC 14869; 10, Lactobacillus delbrueckii ATCC 9649; 11, Leuconostoc mesenteroides IOEB 8293.
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FIG.7. PCR amplification of sequences from various lactic acid bacteria, homologous to the ABC domain of ftsH. The amplified sequences were aligned and compared. oeni, O. oeni; mesen, Leuconostoc mesenteroides; delbru, Lactobacillus delbrueckii; buch, Lactobacillus buchneri; hilg, Lactobacillus hilgardii; acidi, P. acidilactici ATCC 8042; pento, P. pentosaceus; damno, P. damnosus; fruct, Lactobacillus fructivorans; plant, Lactobacillus plantarum; saliv, Lactobacillus salivarius ATCC 11740; dextri, P. dextrinicus; lactis, L. lactis. An asterisk below the sequences indicates a perfect consensus between the protein sequences. Dots indicate conservative substitutions. The Walker B motif and the SRH domain are indicated. The consensus SRH sequence is outlined above the black bar. Dashes indicate gaps introduced to optimize the alignment.
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ftsH mutant when grown at 37°C. The salt- and temperature-induced ftsH gene expression in O. oeni is in keeping with the reported observation that in L. lactis most of the salt-induced proteins were also induced by heat shock (10). We have shown here that the ftsH gene is one of the molecular devices in O. oeni that might enable this species to cope better with high fermentation temperatures. In addition, the O. oeni FtsH protein conferred protection against wine toxicity to the E. coli
ftsH mutant. This ability is shared not only by the O. oeni homologue but also by the B. japonicum counterpart. Since this ability was tested in a foreign host, E. coli, one can speculate that it is likely to be shared by the FtsH proteins of many other species. FtsH proteins belong to the AAA protein family (11), which constitutes a distinct subfamily of the Walker-type ATPases. In addition to the two consensus motifs, Walker A and B, in the Walker-type ATPases, AAA proteins have another highly conserved amino acid sequence within their ATPase domain, the SRH. The SRH plays an important role in ATP hydrolysis, and some highly conserved amino acid residues within the SRH were found to be essential for the in vivo protease activity of FtsH (9).
Alignment of the 13 sequences of the FtsH ATPase domains from various lactic acid bacteria defined an SRH consensus (Fig. 7). This consensus differs in only two positions from the SRH consensus obtained by comparison of 54 representative AAA proteins (9). However, these two differences, I297 M and P303S (the numbering is that of the E. coli FtsH protein), affect only poorly conserved residues of the SRH, which are not essential for FtsH activity. Indeed, the activity of a P303A mutant of the E. coli FtsH protein is almost the same as that of a wild-type FtsH protein (9). The highly conserved residues N301, D307, L310, R312, and R315, on the other hand, which are critical for E. coli FtsH activity, belong to the lactic acid bacterial consensus sequence. In conclusion, the lactic acid bacterial sequences collected are likely to be part of authentic and active FtsH proteins. Thus, FtsH is probably a universal molecular device, at least throughout the prokaryotic kingdom.
ftsH strain AR3291. We also thank Amélie Vallet for technical assistance. |
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32, the heat shock regulator in Escherichia coli, is governed by HflB. Proc. Natl. Acad. Sci. USA 92:3516-3520.
32 in vivo. Mol. Microbiol. 50:583-593.
32. EMBO J. 14:2551-2560.[Medline]
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