Dr. Yeo Chew Chieng

E-mail:
Tel:	603 7880 1777 (ext 126)

Research Interests

• Toxin-antitoxin systems in bacterial pathogens
  
  
• Molecular biology of aromatic hydrocarbon degradation in Pseudomonas
  
  
  
  

Pseudomonas alcaligenes NCIB 9867 (strain P25X) is an environmental isolate that is capable of degrading xylenols and cresols via the gentisate pathway of aromatic hydrocarbon degradation. The relatively high rate of isolating P25X mutants that are incapable of growing on aromatic compounds hints at the mobility of the genes involved in their degradation and the plasticity of the P25X genome. Indeed, several functional insertion sequence (IS) elements, transposons and a mobile group II intron have been isolated and characterized from the P25X genome.

We have recently cloned several genes from strain P25X that are involved in the gentisate pathway. We are interested to elucidate how the expression of these genes is regulated as P25X is known to possess two copies of several of the gentisate pathway enzymes.

P25X also harbors an endogenous 32.7 kb plasmid designated pRA2. Previous attempts to obtain a plasmid-free derivative of strain P25X have been unsuccessful and sequence analysis of pRA2 revealed that the plasmid encodes for at least two plasmid stability modules. A restriction-modification system designated Pac25I acts as a poison-antidote system, with the endonuclease digesting any DNA of plasmid-free segregants that have not been methylated by the corresponding methyltransferase which acts as the antidote. The stability of pRA2 is also contributed by an active plasmid partitioning module, parAB.

A potential third plasmid stability determinant was detected in a pRA2-encoded open reading frame that bears structural homology with the recently-elucidated crystal structure of the ζ protein which is part of the εζ toxin-antitoxin module of the Streptococcus pyogenes plasmid pSM19035 [Meinhart et al. (2003) Proc. Natl. Acad. Sci. USA 100: 1661-1666]. Homologs of εζ could be found on a number of bacterial genomes where it is postulated to be involved in programmed cell death (PCD). We are interested to investigate the εζ homolog on pRA2 and use that as a model for studying the putative PCD modules in other bacteria, in particular, Streptococcus pneumoniae. The toxins of addiction modules are biotechnologically important because they represent an enormous reservoir of potentially useful antibiotics. Understanding the genetic regulation of these PCD modules would enable us to utilize them, not only to kill selective bacteria, but also to contain bacteria used in biotechnology.

Selected publications

• Khoo, S. K., Loll, B., Chan, W. T., Shoeman, R. L., Ngoo, L., Yeo, C. C., and A. Meinhart (2007) Molecular and structural characterization of the PezAT chromosomal toxin-antitoxin system of the human pathogen Streptococcus pneumoniae. Journal of Biological Chemistry 282: 19606 – 19618.
  
  
• Neito, C., Cherny, I., Khoo, S. K., de Lacoba, M. G., Chan, W. T., Yeo, C. C., Gazit, E., and M. Espinosa (2007) The yefM-yoeB toxin-antitoxin systems of Escherichia coli and Streptococcus pneumoniae: functional and structural correlation. Journal of Bacteriology 189: 1266 – 1278.
  
  
• Zhao, B., Yeo, C. C, Tan, C. L., and C. L Poh (2007) Proteome analysis of heat shock protein expression in Pseudomonas alcaligenes NCIMB 9867 in response to gentisate exposure and elevated growth temperature. Biotechnology and Bioengineering 97: 506 – 514.
  
  
• Gao, X., Tan, C. L., Yeo, C. C., and C. L. Poh (2005) Molecular and biochemical characterization of the xlnD-encoded 3-hydroxybenzoate 6-hydroxylase involved in the degradation of 2,5-xylenol via the gentisate pathway in Pseudomonas alcaligenes NCIMB 9867. Journal of Bacteriology 187: 7696 – 7702.
  
  
• Tan, C. L., Yeo, C. C., Khoo, H. E., and C. L. Poh (2005) Replacement of tyrosine-181 by phenylalanine in gentisate 1,2-dioxygenase I from Pseudomonas alcaligenes NCIMB 9867 enhances catalytic activities. Journal of Bacteriology 187: 7543 – 7545.
  
  
• Yeo, C. C., and C. L. Poh (1996) IS1394 from Pseudomonas alcaligenes NCIB 9867: identification and characterization of a member of the IS30 family of insertion elements. Gene 175, 109 - 113.
  
  
• Yeo, C. C., J. M. Tham, M. W. C. Yap, and C. L. Poh (1997) Group II intron from Pseudomonas alcaligenes NCIB 9867 (P25X): entrapment in plasmid RP4 and sequence analysis. Microbiology 143, 2833 - 2840.
  
  
• Yeo, C. C., J. M. Tham, S. M. Kwong, S. Yiin, and C. L. Poh (1998) Tn5563, a transposon encoding putative mercuric ion transport proteins located on plasmid pRA2 of Pseudomonas alcaligenes. FEMS Microbiology Letters 165, 253 - 260.
  
  
• Yeo, C. C., J. M. Tham, S. M. Kwong, and C. L. Poh (1998) Characterization of the Pac25I restriction-modification genes isolated from the endogenous pRA2 plasmid of Pseudomonas alcaligenes NCIB 9867. Plasmid 40, 203 - 213.
  
  
• Kwong, S. M., C. C. Yeo, A. Suwanto, and C. L. Poh (2000) Characterization of the endogenous plasmid from Pseudomonas alcaligenes NCIB 9867: DNA sequence and mechanism of transfer. Journal of Bacteriology 182 : 81 - 90.
  
  
• Kwong, S. M., C. C. Yeo, and C. L. Poh (2001) ParB autoregulates parAB transcription and forms a nucleoprotein complex at the plasmid partitioning site parS. Molecular Microbiology 40 : 621 - 633.
  
  
• Yeo, C. C., S. Yiin, B. H. Tan, and C. L. Poh (2001) Isolation and molecular characterization of group II introns from Pseudomonas alcaligenes and Pseudomonas putida. Plasmid 45 : 233 - 239.
  
  
• Chua, C. H., Y. M. Feng, C. C. Yeo, H. E. Khoo, and C. L. Poh (2001) Identification of amino acid residues essential for catalytic activity of gentisate 1,2-dioxygenase from Pseudomonas alcaligenes NCIB 9867. FEMS Microbiology Letters 204 : 141 - 146.
  
  
• Yeo, C. C., M. V. Wong, Y. Feng, K. P. Song, and C. L. Poh (2003) Molecular characterization of an inducible gentisate 1,2-dioxygenase gene, xlnE, from Pseudomonas alcaligenes NCIMB 9867. Gene 312: 239 – 248
  
  
• Zhao, B., C. C. Yeo, C. C. Lee, A. Geng, F. T. Chew, and C. L. Poh (2004) Proteome analysis of gentisate-induced response in Pseudomonas alcaligenes NCIB 9867. Proteomics (in press)

Selected conference proceedings

• Y. Feng, C. C. Yeo, and C. L. Poh (2000) Molecular characterization of gentisate 1,2-dioxygenase from Pseudomonas alcaligenes NCIB 9867. In: Abstracts of the 9th Biocatalysis and Bioprocessing Conference: Biocatalyst Design Through Genomics, October 30 - November 1, University of Iowa, USA. pp 60.
  
  
• C. C. Yeo, B. H. Tan, G. K. Loh, and C. L. Poh (2001) Natural transformation system in Pseudomonas alcaligenes NCIB 9867. In: Abstracts of the Pseudomonas 2001 Conference, September 17 - 21, Brussels, Belgium.
  
  
• C. C. Lee, A. Geng, C. C. Yeo, and C. L. Poh (2002) Application of gene-based technologies to bioremediation. In: Abstracts of the Third International Conference on Remediation of Chlorinated and Recalcitrant Compounds. May 20 - 23, Monterey, California.
  
  
• C. L. Poh and C. C. Yeo (2002) Mobile genetic elements of Pseudomonas alcaligenes NCIB 9867. Invited speaker at the 9th International Symposium on the Genetics of Industrial Microorganisms (GIM - 2002), July 1 - 5, Gyeongju, Korea.