|
|
|
|
|
|
Characterization of Two Cryptic Helicobacter pylori Plasmids: a Putative Source for Horizontal Gene Transfer and Gene Shuffling. Dirk Hofreuter, 2002.Many Helicobacter pylori isolates carry cryptic plasmids of extremely variable size . In this study we analyzed two H . pylori plasmids, pHel4 and pHel5, from H . pylori strains P8 and P29, respectively . Plasmid pHel4 consists of 10,970 bp, constituting 15 putative open reading frames (ORFs), whereas pHel5 consists of 18,291 bp, constituting 17 ORFs . The findings that both plasmids encode a conserved RepA protein and that both have an origin of replication containing an iteron place them in the group of theta plasmids . In pHel4, the products of the overlapping orf4C, orf4D, orf4E, and orf4F sequences are homologous to MobA, MobB, MobC, and MobD, encoded by colicinogenic plasmids, suggesting that pHel4 might be mobilizable . A further putative operon consists of orf4B and orf4A, the products of which are homologous to microcin C7 (MccC7) biosynthesis and secretion proteins MccB and MccC, respectively . Plasmid pHel5 carries putative genes encoding proteins with homology to an endonuclease and gene products of an H . pylori chromosomal plasticity zone . Both plasmids contain repeat sequences, such as the previously identified R2 repeat, which are considered preferred recombination sites . In pHel4, a new repeat sequence (R4 repeat), which seems to act as a hot spot for site-specific recombination, was identified . All H . pylori plasmids characterized so far have a modular structure . We suggest a model that explains the existing plasmids by insertions and deletions of genetic elements at the repeat sequences . A genetic exchange between plasmids and the bacterial chromosome, combined with plasmid mobilization, might add a novel mechanism to explain the high genetic macrodiversity within the H . pylori population . Porphyrin-Mediated Cell Surface Heme Capture from Hemoglobin by Porphyromonas gingivalis. Mayuri Paramaesvaran, 2003.The porphyrin requirements for growth recovery of Porphyromonas gingivalis in heme-depleted cultures are investigated . In addition to physiologically relevant sources of heme, growth recovery is stimulated by a number of noniron porphyrins . These data demonstrate that, as for Haemophilus influenzae, reliance on captured iron and on exogenous porphyrin is manifest as an absolute growth requirement for heme . A number of outer membrane proteins including some gingipains contain the hemoglobin receptor (HA2) domain . In cell surface extracts, polypeptides derived from HA2-containing proteins predominated in hemoglobin binding . The in vitro porphyrin-binding properties of a recombinant HA2 domain were investigated and found to be iron independent . Porphyrins that differ from protoporphyrin IX in only the vinyl aspect of the tetrapyrrole ring show comparable effects in competing with hemoglobin for HA2 and facilitate growth recovery . For some porphyrins which differ from protoporphyrin IX at both propionic acid side chains, the modification is detrimental in both these assays . Correlations of porphyrin competition and growth recovery imply that the HA2 domain acts as a high-affinity hemophore at the cell surface to capture porphyrin from hemoglobin . While some proteins involved with heme capture bind directly to the iron center, the HA2 domain of P . gingivalis recognizes heme by a mechanism that is solely porphyrin mediated . Isolation and Antifungal and Antioomycete Activities of Aerugine Produced by Pseudomonas fluorescens Strain MM-B16. Jung Yeop Lee, 2003.The bacterial strain MM-B16, which showed strong antifungal and antioomycete activity against some plant pathogens, was isolated from a mountain forest soil in Korea . Based on the physiological and biochemical characteristics and 16S ribosomal DNA sequence analysis, the bacterial strain MM-B16 was identical to Pseudomonas fluorescens . An antibiotic active against Colletotrichum orbiculare and Phytophthora capsici in vitro and in vivo was isolated from the culture filtrates of P . fluorescens strain MM-B16 using various chromatographic procedures . The molecular formula of the antibiotic was deduced to be C10H11NO2S (M+, m/z 209.0513) by analysis of electron impact mass spectral data . Based on the nuclear magnetic resonance and infrared spectral data, the antibiotic was confirmed to have the structure of a thiazoline derivative, aerugine [4-hydroxymethyl-2-(2-hydroxyphenyl)-2-thiazoline] . C . orbiculare, P . capsici, and Pythium ultimum were most sensitive to aerugine (MICs for these organisms were approximately 10 µg ml-1) . However, no antimicrobial activity was found against yeasts and bacteria even at concentrations of more than 100 µg ml-1 . Treatment with aerugine exhibited a significantly high protective activity against development of phytophthora disease on pepper and anthracnose on cucumber . However, the control efficacy of aerugine against the diseases was in general somewhat less than that of the commercial fungicides metalaxyl and chlorothalonil . This is the first study to isolate aerugine from P . fluorescens and demonstrate its in vitro and in vivo antifungal and antioomycete activities against C . orbiculare and P . capsici .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
