Research in this lab is carried out in collaboration with the Errington group, using Gram-positive bacterium Bacillus subtilis as a model system. We are interested in three areas.
Bacterial cell wall biosynthesis:
Bacterial cell wall helps to maintain cell shape but most importantly it provides protection to the cells, and has been one of the targets for antibiotics. However, the mechanisms involved in cell wall biosynthesis are still poorly understood. Most of the analysis has been restricted to either the biosynthetic pathway required for synthesis of the major cell wall precursors (e.g. mur or mra genes) or the final steps of peptidoglycan synthesis (carried out by penicillin-binding proteins). Very little is known about the intermediate steps whereby the precursors are exported from the cytoplasm to the outside of the cell and incorporated into the existing structure to allow cell enlargement or division. Recent studies have provided evidence for specific complexes, (cytoskeletal structures) central to these events. However, the mechanism and the functional components of these complexes have yet to be clearly defined. Thus, there are many areas to explore, including peptidoglycan precursor export and incorporation, cell wall maturation and degradation, secondary polymer biosynthesis, export and incorporation (e.g. teichoic acids).
This work will mainly utilise B. subtilis as a model system, but may also touch on Corynebacterium glutamicum, Staph. aureus and Strep. pneumonia for comparison due to their interesting morphological diversity.
Bacterial cell division:
Cell division requires co-ordinated synthesis and invagination of both the membrane and cell wall material (i.e. peptidoglycan) at the division site. At least 8 essential cell division proteins assemble into a complex that is responsible for the formation of a division septum in B. subtilis. Surprisingly, given their importance, so far, only two of them have had biochemical activities assigned to them. Characterisation of the division proteins is complicated by the fact that some form a multicomponent machine that spans the cell membrane and loss of any one protein destabilises the complex. Current work is focused on further defining the interaction domains of the DivIB, DivIC, FtsL and PBP 2B proteins. Also, on starting to devise ways to determine the relationship between the structure and the biochemical functions of these proteins in septum formation. Our previous work has revealed specific interactions between proteins involved in the synthesis of peptidoglycan. Validation of these interactions and determination of the interaction domains will be carried out (collaboration with P. Noirot, INRA France).
In addition, a parallel analysis of the division genes in Gram-positive cocci and Corynebacterium glutamicum is being initiated.
Cellular response to phage infection at the transcriptional level. The bacteriophage 29 has been extensively studied with respect to the expression and function of the individual phage-encoded proteins. However, relatively little attention has been paid to the host organism (B. subtilis). It is unknown how the bacterial cell responds to the invasion of its cytoplasm and for that matter if the phage exerts any regulation on cellular processes. It is proposed to use microarray analysis of mRNA through the infection cycle to determine how the host responds to infection. (Joint project with W. Meijer, Spain)