Round-cell mutants of Salmonella typhimurium produced by transposition mutagenesis: Lethality of rodA and mre mutations

Costa, Carolina Ortiz Rocha da; Antón, Dora N.

doi:10.1007/bf00277138

Cited by 29 publications

(31 citation statements)

References 30 publications

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“…The rodshaped organism B. subtilis, for example, has three mreB-like genes, namely, mreB, mbl (mreB-like), and mreBH. MreB appears to be essential in all bacteria studied so far, including B. subtilis (80,166), E. coli (88), C. crescentus (52), Rhodobacter sphaeroides (156), Salmonella enterica serovar Typhimurium (19,20), and Streptomyces coelicolor (9,112). In E. coli, mreB mutants are spherical, and MreB was inferred not to be essential for many years (170,171), but a recent report showed that MreB is indeed essential in this bacterium, too (88).…”

Section: The Bacterial Actin Mrebmentioning

confidence: 99%

The Bacterial Actin-Like Cytoskeleton

Carballido-López

2006

Microbiol Mol Biol Rev

177

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SUMMARY Recent advances have shown conclusively that bacterial cells possess distant but true homologues of actin (MreB, ParM, and the recently uncovered MamK protein). Despite weak amino acid sequence similarity, MreB and ParM exhibit high structural homology to actin. Just like F-actin in eukaryotes, MreB and ParM assemble into highly dynamic filamentous structures in vivo and in vitro. MreB-like proteins are essential for cell viability and have been implicated in major cellular processes, including cell morphogenesis, chromosome segregation, and cell polarity. ParM (a plasmid-encoded actin homologue) is responsible for driving plasmid-DNA partitioning. The dynamic prokaryotic actin-like cytoskeleton is thought to serve as a central organizer for the targeting and accurate positioning of proteins and nucleoprotein complexes, thereby (and by analogy to the eukaryotic cytoskeleton) spatially and temporally controlling macromolecular trafficking in bacterial cells. In this paper, the general properties and known functions of the actin orthologues in bacteria are reviewed.

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Section: The Bacterial Actin Mrebmentioning

confidence: 99%

The Bacterial Actin-Like Cytoskeleton

Carballido-López

2006

Microbiol Mol Biol Rev

177

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“…Genes affecting bacterial cell shape are typically essential for viability (9), which may explain our failure to obtain an apf double knockout. Double inactivation of apf genes was also unsuccessful in L. johnsonii NCC533 (La1) (34), suggesting that the physiological function of APF is essential.…”

Section: Discussionmentioning

confidence: 99%

Contribution of Aggregation-Promoting Factor to Maintenance of Cell Shape in Lactobacillus gasseri 4B2

et al. 2003

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Aggregation-promoting factor (APF) was originally described as a protein involved in the conjugation and autoaggregation of Lactobacillus gasseri 4B2, whose corresponding apf gene was cloned and sequenced. In this report, we identified and sequenced an additional apf gene located in the region upstream of the previously published one. Inactivation of both apf genes was unsuccessful, indicating that APF function may be essential for the cell. Overproduction of APF proteins caused drastic alteration in the cell shape of this strain. These cells were irregular, twisted, enlarged, and tightly bound in unbreakable clumps of chains. Down-regulation of APF synthesis was achieved by cloning of the apf2 promoter region on a high-copy-number plasmid, which recruited a putative apf activator. As a consequence, the shape of the corresponding recombinant cells was elongated (filamentous) and cell division sites were no longer visible. None of the induced changes in APF production levels was clearly correlated with modifications of the aggregation phenotype. This report shows, for the first time, that APF proteins are mainly critical for L. gasseri 4B2 cell shape maintenance.Lactic acid bacteria are normal inhabitants of the human oral cavity and gastrointestinal (GI) and urogenital tracts. Interest in the health-promoting effects of specific lactic acid bacterial strains has increased in recent years (10, 12). Survival and persistence of probiotic bacteria in the human GI tract is often reported to provide them a competitive advantage. One of the proposed mechanisms that could increase the potential of bacteria to survive and persist in the GI tract is their ability to aggregate (13). However, this hypothesis has never been confirmed.To study the importance of aggregation, we chose an aggregating strain, Lactobacillus gasseri 4B2 (previously classified as L. plantarum 4B2), whose 32-kDa aggregation-promoting factor (APF) has already been described (25). This protein was purified from the culture supernatant as one of the most abundant proteins. The function of APF as a factor of aggregation was shown in vitro. After three subsequent washing steps, L. gasseri 4B2 lost its ability to aggregate. Addition of purified APF or of filtered supernatant reaggregated the washed cells. Furthermore, the role of APF in conjugation was also demonstrated (25). The frequency of pAM␤1 conjugal transfer (among Lactobacillus species whose aggregation is APF dependent) was increased upon addition of L. gasseri 4B2 filtered supernatant to the mating mixture. Since neither the apf gene nor any apf mutant was available, the exact physiological role of APF could not be demonstrated. Subsequent N-terminal sequencing of the L. gasseri 4B2 APF protein enabled the cloning and sequencing of the apf gene (accession no. Y08498; L. Morelli et al., direct submission).Recently, we showed that four L. johnsonii and two L. gasseri strains contain two apf genes in their genomes (34). Analysis of the gene organization, amino acid composition, and physical propert...

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“…Although 6.6% of the isolates were resistant, none was positive for ␤-lactamase. Amoxicillin resistance develops due to structural alterations in one of the penicillin-binding proteins (4,5,9) or changes in other proteins involved in cell wall synthesis (2,15,26), and the resistant phenotype may be lost due to freezing or storage. All isolates tested in the present study were frozen at least once, and the low prevalence of the resistance phenotype may be due to loss during storage.…”

Section: Eradication Ofmentioning

confidence: 99%

Antimicrobial Susceptibility of Helicobacter pylori Strains Isolated in Bangladesh

et al. 2004

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Antimicrobial susceptibility of 120 Helicobacter pylori isolates to metronidazole, tetracycline, clarithromycin, and amoxicillin was determined, and 77.5, 15, 10, and 6.6% of the isolates, respectively, were resistant. Only rdxA inactivation and both rdxA and frxA inactivation were responsible for metronidazole resistance in 66% (8 of 12) and 33% (4 of 12) of the isolates, respectively. Eradication ofHelicobacter pylori infection by treatment with two antimicrobial agents (clarithromycin and amoxicillin or metronidazole) and a proton pump inhibitor is recommended by various consensus groups (10,16,20). Antimicrobial resistance in H. pylori is a growing problem as it is the most important factor in determining treatment outcome. The prevalence of antimicrobial resistance varies with geographical regions (3, 25). Metronidazole resistance in H. pylori has been shown to be due to mutation in rdxA; mutation in frxA has also been shown to be associated with metronidazole resistance (11,12,23). In Bangladesh, the prevalences of H. pylori infection among infants, children, and adults are 61, 84, and 92%, respectively (1, 21, 22); however, information on antimicrobial susceptibility to commonly used drugs in H. pylori treatment is lacking. This study was conducted to evaluate (i) the prevalence of primary antibiotic resistance to commonly used antimicrobial agents and (ii) the genetic basis for metronidazole resistance in H. pylori isolates from Bangladesh.Consecutive patients attending the Gastroenterology Department of Dhaka Medical College Hospital for upper gastrointestinal endoscopy were enrolled during 1999 to 2001. Diagnosis of peptic ulcer (PU) and non-ulcer dyspepsia (NUD) or gastritis was based on endoscopic examination of the stomach and duodenum. Biopsy samples were taken from each patient for culture.Bacteria were grown in brain heart infusion agar with 7% sheep blood and incubated at 37°C in 5% O 2 , 10% CO 2 , and 85% N 2 for 3 to 6 days. The MICs of amoxicillin, clarithromycin, metronidazole, and tetracycline for the isolates were determined by the agar dilution method as described elsewhere (18,19). All tests were repeated twice, and H. pylori 26695 was used as a control. ␤-Lactamase production was tested by the chromogenic cephalosporin method (6). The molecular mechanism of susceptibility and resistance to metronidazole was studied in 12 isolates. Metronidazole-susceptible (Mtz s ) isolates were further studied (by inactivation of rdxA alone or rdxA and frxA for conversion into an Mtz r phenotype) by transformation of Mtz s isolates with plasmids pBS-rdxA-cam (rdxA::cat) and pBS-frxA-kan (frxA::kan) as described earlier (11,12).A total of 278 consecutive patients between 15 and 78 years of age were enrolled, and among them, 72.7% (202 patients) were male and 27.3% (76 patients) were female. Among the patients, 162 had PU and 116 had NUD and 62.6% (174 of 278) were culture positive for H. pylori. Among the culturepositive patients, 121 (69.5%) were male and 53 (30.4%) were female and 112 (64.3%) had PU ...

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Round-cell mutants of Salmonella typhimurium produced by transposition mutagenesis: Lethality of rodA and mre mutations

Cited by 29 publications

References 30 publications

The Bacterial Actin-Like Cytoskeleton

The Bacterial Actin-Like Cytoskeleton

Contribution of Aggregation-Promoting Factor to Maintenance of Cell Shape in Lactobacillus gasseri 4B2

Antimicrobial Susceptibility of Helicobacter pylori Strains Isolated in Bangladesh

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