Deepti Deepika's Talk

Sep 16, 2013 - 17:00

Sep 16, 2013 - 18:00

Creativity Hall (Room #118) Chemical Engineering Department

Seminars

Deepti Deepika has been a PhD student in this department since January 2008. She finished her undergraduate studies in Life Sciences in 2005 and master’s in Biotechnology in 2007 from Utkal University Bhubaneswar.

Abstract: All microorganisms need to respond and adapt to their environment in order to survive and one of the ways to escape from challenging environments is to migrate. Chemotaxis is the biased migration of microorganisms to reach high nutrient concentrations and escape from noxious substances to ensure optimal growth and survival conditions. The chemotaxis phenomenon has been studied extensively in Escherichia coli which achieves the biased motion by altering the rotational direction of its flagella. Counter-clockwise (CCW) rotation as viewed from the flagella end of the cell results in a motion called run whereas clockwise (CW) rotation leads to tumbling of the bacteria. By modulating the duration of motor bias and therefore the duration of runs the bacteria achieve a net motion towards favorable chemicals or away from repellents. The regulation of the motor bias is achieved through a well-characterized signaling pathway which involves sensing of the ligand through a membrane sensor response through a signaling pathway and adaptation to the new environment. The current understanding of the molecular basis for chemotaxis comes from characterization of the high-abundance receptors namely Tar and Tsr which are responsible for sensing the amino acids asparate and serine respectively. Apart from the Tar and Tsr receptors E. coli senses its environment through three low-abundance receptors of which the Trg receptor is used to detect glucose. While detailed studies have focused on the molecular mechanism of sensing and adaptation via the Trg receptor the latter is yet to be characterized in terms of the phenotypic response namely run speed and motor bias. In addition glucose is also sensed through a Phospho Transferase System (PTS) sugar uptake mechanism which operates in conjunction with the receptor mediated response through Trg. Our experiments investigate the response of the cell to glucose and a non-metabolizable analogue of glucose. At steady state both the motor bias and the run speed vary with the ligand concentration suggesting an imperfect adaptation. When exposed to a gradient the bias and the run speed are modulated to achieve drift velocities that are much higher than those achieved through the modulation of the bias alone. A strain lacking the Trg sensor exhibits run speeds much lower than that observed for the wild type strain in motility buffer suggesting that the Trg sensor influences the motor characteristics. We measure individual contributions of the two mechanisms on the run speed and the motor bias and show that the chemotactic response of a WT strain to glucose is the sum of contributions from the two mechanisms (Trg sensing and PTS). The CW bias and the mean run speed varies with ligand concentration indicating not only an imperfect adaptation but also a modulation of run speed. The main implication of our study is that E. coli modulates the motor characteristics not only by varying both the duration of run and tumble but also the run speed to affect chemotaxis and thereby efficiently sample its nutritionally rich environment. Keywords: Chemotaxis E. coli receptor mediated sensing PhosphoTransferase System Glucose sensing bacterial motor characteristics.About the Speaker: Deepti Deepika has been a PhD student in this department since January 2008. She finished her undergraduate studies in Life Sciences in 2005 and master’s in Biotechnology in 2007 from Utkal University Bhubaneswar. She joined the PhD program under Prof K V Venkatesh and Prof Mahesh S Tirumkudulu on the DST project: Chemotaxis in E. coli and phenotypic characterization of the cellular responses involved. Apart from studying cellular and behavioural responses her research interests include cell biology understanding the intracellular molecular mechanisms of pathogenesis drug development and immunology. After completing her PhD she is willing to pursue a post doctoral research career in one of these areas.