P. Ajitkumar, PhD
Associate Professor
Department of Microbiology and Cell Biology
Indian Institute of Science, Bangalore, India
Tel: 080-2293-2344, Fax No. - 91-80-23602697, Email: ajit@mcbl.iisc.ernet.in

   

Main Research Interests

The Mechanisms, the Biology, and the Physiological Significance of Cell Division in Mycobacteria and Escherichia coli under normal and stress conditions

Experimental Systems: Mycobacterium tuberculosis, Mycobacterium smegmatis, Mycobacterium xenopi, Mycobacterium leprae, and Escherichia coli

Cellular and Molecular Processes Studied: 1. Transcriptional regulation of cell division genes; 2. Proteins that interact with and modulate function of the principal cell division protein, FtsZ; 3. Protease(s) that regulate the levels of FtsZ; 4. Mechanism of regulation of cell division in non-replicating persistent (NRP) Mycobacterium tuberculosis cells and in other mycobacteria and E. coli under stress conditions; 5. ftsZ antisense RNA that regulates FtsZ synthesis; and 6. Highly deviated asymmetric division in bacterial systems and its mechanisms and physiological significance.

Cell Division Regulation in Mycobacteria and E. coli: Regulation of cell division in tubercle bacilli is a key prerequisite event for the successful establishment of infection and survival under dormant condition in TB patients. Cell division in tubercle bacilli gets shut down when the bacilli enter non-replicating persistence (NRP) state (dormancy/latency) in granuloma in TB patients. When immunodebilitative conditions prevail in the host, through reactivation of cell division, NRP bacilli come out of dormancy and proliferate. Moreover, when a TB patient is cured, the person is cured of only the proliferating cells, but not of dormant (non-proliferating) bacilli that might exist, as the TB drugs presently in vogue destroy only proliferating bacilli but not dormant (non-proliferating) bacilli. Thus, in order to combat dormant bacilli, there is a dire need to identify molecules and machinery, which are vital to the bacilli for the establishment of dormancy, or survival during dormancy or reactivation from dormancy.
The second major problem that stands against TB eradication in India is the necessity for the prolonged six months of treatment, which forces the patients from the financially poor sections of the society, which form the major proportion of TB patients in India, to discontinue treatment to facilitate going for livelihood means, thereby generating drug-resistant bacilli. This problem can be solved, especially in the countries where the per capita income is low, only if the treatment period is brought down to few weeks.
In order to find out solutions to these two major problems in TB cure/eradication, research work is being carried out in my laboratory to find out: (i). the molecules and machinery, which are vital to the bacilli for the establishment of dormancy, survival during dormancy, or reactivation from dormancy; (ii). the bacterial factors responsible for the persistence under stress conditions, thereby necessitating prolonged treatment; and (iii). the mechanisms and machinery required to bring about cell division regulation under various stress conditions for the survival of the pathogen.

The Bacterial Cell Division Molecules Studied in the Laboratory: Bacterial cell division consists of nucleoid replication and segregation of daughter nucleoids (karyokinesis), followed by the formation of septum at the mid-cell site of the parent cell (septation/cytokinesis). We have identified, cloned and expressed several cytokinetic proteins, FtsZ, FtsH, FtsE, FtsX, and FtsQ from M. tuberculosis, and structural and functional roles of these proteins, and regulation of expression of these genes in M. tuberculosis cells entering dormancy are being studied. Several non-Fts proteins and their genes, such as Fic and NDK, which are presumed to connect cell division machinery to cellular metabolism, are also being studied in mycobacteria. In parallel to these studies, mechanisms of cytokinesis in E. coli cells are also under investigation.

Unique Modes of Cell Division in Mycobacteria - their Mechanism and Physiological Significance: We recently discovered an unusual type of cell division in mycobacteria - highly deviated asymmetric division, where the cell division occurs at 17-24% away from the mid-cell site (Vijay et al 2014a, b). About 20-30% of the septating population of cells alone divides in this manner. As discovered by us and also by three other groups in parallel, the remaining 80% of the cells in the septating population divide by symmetric division but with only 5-10% variation in the division position. In the unique mode of highly deviated asymmetric division, the mother cell divides highly unequally to generate a short cell and a long cell. Both the short cell and the long cell further grow and undergo division symmetrically or again highly asymmetrically, to generate cell size heterogeneity in the population. The mechanisms of highly deviated asymmetric division and the physiological significance thereof are being investigated in both the pathogenic and nonpathogenic mycobacteria.

 

Some Important Publications

Vijay, S., Nagaraja, M., Sebastian, J. and Ajitkumar, P. (2014a) Asymmetric cell division in Mycobacterium tuberculosis and its unique features. Archives of Microbiology 196, 157-168.

Vijay, S., Nagaraja, M., and Ajitkumar, P. (2014b) Highlydeviated asymmetric division in very low proportion of Mycobacterial mid-log phase cells. The Open MicrobiologyJournal8, 40-50

Arumugam, M. and Ajitkumar, P. (2013) Heat and SDS insensitive NDK dimers are largely stabilised by hydrophobic interaction to form functional hexamer in Mycobacterium smegmatis. Acta Biochimica Polonica 60, 199-207.

Vijay S, Anand, D. and Ajitkumar P. (2012) Unveiling Unusual Features of Formation of Septal Partition and Constriction in Mycobacteria -- an Ultrastructural Study. Journal of Bacteriology 194, 702-707.

Roy, S., Narayana, Y., Balaji, K. N. and Ajitkumar, P. (2012) Highly fluorescent GFPm2+-based genome integration-proficient promoter probe vector to study Mycobacterium tuberculosis promoters in infected macrophages. Microbial Biotechnology 5, 98-105.

Mishra, S., Bhagavat, R., Chandra, N., Vijayarangan, N., Rajeswari, H. and Ajitkumar, P. (2012) Cloning, expression, purification, and biochemical characterisation of the FIC motif containing protein of Mycobacterium tuberculosis. Protein Expression and Purification 86, 58-67.

Roy, S., Anand, D., Vijay, S., Gupta, P. and Ajitkumar, P. (2011) The ftsZ gene of Mycobacterium smegmatis is expressed through multiple transcripts. The Open Microbiology Journal 5, 43-53.

Gupta, P., Rajeswari, H., Arumugam, M., Mishra, S., Bhagavat, R., Anand, P., Chandra, N., Srinivasan, R., Indi, S. S. and Ajitkumar, P. (2010) Mycobacterium tuberculosis FtsZ requires at least one arginine residue at the C-terminal end for polymerisation in vitro. Acta Biochimica Biophysica Sinica 42, 58-69.

Roy, S. and Ajitkumar, P. (2005) Transcriptional analysis of principal cell division gene ftsZ of Mycobacterium tuberculosis. Journal of Bacteriology 187, 2540-2550.

Gupta, P., Srinivasan, R., Rajeswari, H., Indi, S. S. and Ajitkumar, P. (2008). In vitro polymerisation of Mycobacterium leprae FtsZ or Mycobacterium tuberculosis FtsZ is revived or abolished respectively by reciprocal mutation of a single residue. Biochemical Biophysical Research Communications 368, 445-452.