We are interested in understanding the mechanisms that promote spontaneous
conversion of nonmucoid Pseudomonas aeruginosa to a fatal mucoid or
alginate-producing form and the mechanisms involved in spontaneous reversion
back to nonmucoid form observed under laboratory conditions.
Early aggressive antibiotic therapy is able to eradicate initial and intermittent
colonization of the CF lungs by P. aeruginosa (4). However, when the
colony morphology of bacteria isolated from sputum samples is observed to
convert to the Alg+ form, the organisms can no longer be eliminated
from the lungs despite aggressive antibiotic therapy (4). The selection pressure
for mucoid conversion common to P. aeruginosa strains that thrive in
the complex CF respiratory environment is not well understood. However, in
a recent study Mathee et al established that repeated exposure of a P.
aeruginosa biofilm in vitro to activated polymorphonuclear leukocytes
(PMNs), or to low-levels of hydrogen peroxide, can give rise to mucoid variants
with defects in mucA gene, mimicking that seen in vivo (6).
The Alg+ phenotype seen in the CF isolates is extremely unstable (5,
7, 8). Low oxygen tension growth of mucoid variants readily selects for nonmucoid
variants (7). The locus responsible for the switching off mechanism in a CF
isolate FRD has been earlier mapped to algT locus (2, 3). Subsequently,
the molecular basis for this conversion was partially attributed to mutations
in algT (algU) gene itself (1, 8). Previously, we constructed
an alginate producing variant of PAO1 by replacing the mucA gene with
the allele mucA22 frequently found in CF isolates 6). In order to study
the switch of P. aeruginosa from mucoid to nonmucoid form under defined
conditions we used PDO300 as the mucoid parent strain for isolation of spontaneous
nonmucoid variants. 36 nonmucoid mutants were isolated from PDO300 for analysis.
Preliminary complementation analysis suggested that 10 of the 36 isolates
are likely to have a mutation in the algT gene. Currently, we are investigating
the properties all the 36 isolates: we will be analyzing the production of
virulent factors such as proteases and inducible beta-lactamases levels by biochemical
assays, and quorum-sensing molecules by electron mass spectroscopy.
References Cited:
| DeVries, C. A., and D. E. Ohman. 1994. Mucoid-to-nonmucoid
conversion in alginate-producing Pseudomonas aeruginosa often results
from spontaneous mutations in algT, encoding a putative alternative
sigma factor, and shows evidence for autoregulation. J. Bacteriol. 176:6677-6687. |
| Flynn, J. L., and D. E. Ohman. 1988. Cloning of genes from
mucoid Pseudomonas aeruginosa which control spontaneous conversion
to the alginate production phenotype. J. Bacteriol. 170:1452-1460. |
| Flynn, J. L., and D. E. Ohman. 1988. Use of a gene replacement
cosmid vector for cloning alginate conversion genes from mucoid and nonmucoid Pseudomonas aeruginosa strains: algS controls expression of algT. J. Bacteriol. 170:3228-3236. |
| Frederiksen, B., C. Koch, and N. Høiby. 1997. Antibiotic
treatment of initial colonization with Pseudomonas aeruginosa postpones
chronic infection and prevents deterioration of pulmonary function in cystic
fibrosis. Pediatr. Pulmonol. 23:330-335. |
| MacGeorge, J., V. Korolik, A. F. Morgan, V. Ashe, and B.
Holloway. 1986. Transfer of a chromosomal locus responsible for mucoid colony
morphology in Pseudomonas aeruginosa isolated from cystic fibrosis
patients to Pseudomonas aeruginosa PAO. J. Med. Microbiol. 21:331-336. |
| Mathee, K., O. Ciofu, C. Sternberg, P. W. Lindum, J. I.
Campbell, P. Jensen, A. H. Johnsen, M. Givskov, D. E. Ohman, S. Molin, N.
Hoiby, and A. Kharazmi. 1999. Mucoid conversion of Pseudomonas aeruginosa by hydrogen peroxide: a mechanism for virulence activation in the cystic
fibrosis lung. Microbiology 145:1349-1357. |
| Ohman, D. E., and A. M. Chakrabarty. 1981. Genetic mapping
of chromosomal determinants for the production of the exopolysaccharide
alginate in a Pseudomonas aeruginosa cystic fibrosis isolate. Infect.
Immun. 33:142-148. |
| Schurr, M. J., D. W. Martin, M. H. Mudd, and V. Deretic.
1994. Gene cluster controlling conversion to alginate-overproducing phenotype
in Pseudomonas aeruginosa: Functional analysis in a heterologous
host and role in the instability of mucoidy. J. Bacteriol. 176:3375-3382. |
Mathee Publications:
| 1. Mathee, K., O. Ciofu, M. Givskov, D. E. Ohman, S. Molin, N. Høiby, and A. Kharazmi. 1999. Induction of Pseudomonas aeruginosa alginate production in vivo mediated by inflammatory response in lungs of cystic fibrosis patients. Clinical Microbiology 5:S8-9. |
| 2. Mathee, K., O. Ciofu, C. Sternberg, P. W. Lindum, J. I. Campbell, P. Jensen, A. H. Johnsen, M. Givskov, D. E. Ohman, S. Molin, N. Hoiby, and A. Kharazmi. 1999. Mucoid conversion of Pseudomonas aeruginosa by hydrogen peroxide: a mechanism for virulence activation in the cystic fibrosis lung. Microbiology 145:1349-1357. |
| 3. Mathee, K., C. McPherson, and D. E. Ohman. 1999. Regulation of alginate production in Pseudomonas aeruginosa by mucC(algM) and mucD(algY). (in preparation). |
4. Ohman, D. E., S. Malhotra, S. Jain, K. Mathee, and L. A. Silo-Suh. 1999. Alginate biosynthesis in Pseudomonas aeruginosa: a stress response. Clinical Microbiol 5:5S11-13. |
| 5. Hughes, K. T., and K. Mathee. 1998. The anti-sigma factors. Annu. Rev. Microbiol. 52:231-286. |
| 6. Mathee, K., C. J. McPherson, and D. E. Ohman. 1997. Posttranslational control of the algT (algU)-encoded sigma22 for expression of the alginate regulon in Pseudomonas aeruginosa and localization of its antagonist proteins MucA and MucB (AlgN). J Bacteriol 179:3711-3720. |
| 7. Mathee, K., C. Sternberg, O. Ciofu, P. Jensen, J. Campbell, M. Givskov, D. Ohman, N. Høiby, S. Molin, and A. Kharazmi. 1997. Presented at the Pseudomonas '97. VI International Congress on Pseudomonas: Molecular biology and biotechnology, Madrid, Spain. |
8. Ohman, D. E., K. Mathee, C. J. McPherson, C. A. DeVries, S. Ma, D. J. Wozniak, and M. J. Franklin. 1996. Regulation of the alginate (algD) operon in Pseudmonas aeruginosa, p. 472-483. In T. Nakazawa, K. Furukawa, D. Haas, and S. Silver (ed.), Molecular Biology of Pseudomonads Amer Soc Microbiol, Washington, D.C.
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Students and Postdoctoral fellows involved:
| Visiting Scientist |
|
| Post-doc |
Dr. Zhijun Song |
| Graduate Students |
Mr. Robert Sautter |
| Past students |
Ms. Damaris Ramos (Spring 2002) |
RESEARCH INTERESTS | JOURNALS//CONFERENCES | PUBLICATIONS | GRANT ACTIVITY | SYNERGISTIC ACTIVITY | COLLABORATIONS | SEMINARS/CONFERENCES | CREW | LAB PROTOCOLS | FORMS/TEMPLATES | MANIFESTO | LECTURES | SCIENCE LINKS | GET TO KNOW MATHEE | ALMA MATER | GIRI NARASIMHAN | ALBUM | TRAVEL | BIOMEDICAL HONORS TRACK | SMIDDY HONORS RESEARCH AWARD
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