Life at Interfaces: Understanding the Fluid Dynamics, Transport and Surface Translocation of Bacterial Biofilms

2^ndYear Postdoctoral Fellow

Research Interests:

In many natural environments, bacteria collectively aggregate to exist in densely populated and structurally diverse communities called biofilms. Within these biofilms, cells exhibit a remarkable division of labor, with various subpopulations of cells involved in active motility by flagellar propulsion, production of extracellular polymeric substances and other functions that collectively results in the initiation, growth, propagation, adhesion and dispersion of biofilms to specific chemical and environmental signals.

By using a combination of experimental techniques such as time-lapse microscopy, constructing fluorescent transcriptional reporters for distinct cell types, confocal microscopy, flow visualization, surface texturing and chemical patterning, my research systematically investigates the collective response that governs the bacterial growth and surface interaction of biofilms under a number of different environmental conditions (such as temperature, pH, agar gel concentration, etc.) with Bacillus Subtilis as the model organism.

In addition, I also work on theoretically and computationally modeling the stability of thin viscous sheets under shear with a non-uniform temperature gradient. Such a model has practical applications ranging from the manufacture of ultra-shin glass sheets via the float glass technique, to understanding physical and biological phenomena such as the buckling of bacterial pellicles during colony growth, and geological processes involving wrinkling of lava sheets.

Postdoctoral Projects:
(Under the supervision of L. Mahadevan & S. Rubinstein, School of Engineering & Applied Sciences, Harvard University)

• Buckling instabilities in thin viscous sheets during extensional flows (theory & simulation)
• Characterizing growth & surface translocation in developing Bacillus Subtilis biofilms (experimental)

PhD Dissertation: “Exploring Plastron Stability and Fluid Friction Reduction on Robust Micro-Textured Non-Wetting Surfaces.”

Under the supervision of Robert E. Cohen and Gareth H. McKinley, Department of Chemical & Mechanical Engineering, Massachusetts Institute of Technology.

Research Experience:

 My PhD work involved both experimental and theoretical research at the interface of polymer physics, fluid mechanics, wetting and soft matter. In my thesis, I developed a precise and repeatable spray technique for rapid fabrication of drag- reducing liquid-repellent coatings that can be deployed on a large scale. I used these coatings to study the fundamental problem of how structured liquid-repellent surfaces, which support a composite liquid-air interface, can reduce skin friction in both viscous laminar and turbulent flows in a Taylor-Couette setup, and developed a theoretical model that accounts for the effect of wall slip in near-wall turbulent flows. In addition to this central experimental theme, I have also worked on a mathematical analysis of the gravity driven deformation of drops on non-wetting surfaces, correlating the wetting dynamics on the barbs and barbules of aquatic birds with diving and wing-spreading behavior, and on developing a hierarchical model to design oil-repellent woven fabrics.

Teaching Interests:
During my education at MIT, I was a Teaching Assistant for the Graduate Transport Phenomena Course. I organized weekly help sessions and presented extra lectures for a class of 50 graduate students on subjects including fluid mechanics, heat/mass transfer, partial differential equations and mathematical methods. I have also directly supervised undergraduate & graduate research students on specific projects during my postdoctoral fellowship. I am interested teaching modules in fluids mechanics, transport phenomena, solid mechanics, heat transfer, mass transfer and applied engineering mathematics, amongst other courses such as thermodynamics and statistical mechanics.

Future Direction:

As a research faculty, I would like to continue the philosophy of using experimental and theoretical tools to understand the physicochemical hydrodynamics in complex systems. In this regard, I believe the bacterial biofilm system I am currently studying provides a rich experimental toolbox, with a number of interesting and currently unexplored phenomena to investigate. Specific examples include studying the biofilm rheology and mechanical behavior (e.g., the viscoelastic characterization of the extracellular polymer matrix), fluid dynamics (directional flows of surfactant laden films generated by the bacteria during swarming) to surface interactions (influence of structured coatings on bacterial growth)

The uniqueness of my approach is the ability to perform direct in-situ measurements and quantify the dynamic response within the biofilm (such as spatial localization & switching between various cell types, observing transient response to antibiotics and external stresses, measurement of velocities during swarming, etc.) both at a single cell level and at a colony scale, and directly test and develop biophysical mechanisms governing growth and spreading. The ultimate goal is in designing chemically patterned & textured surfaces that selectively inhibit the growth of living matter on surfaces, and has a number of potential applications such as in preventing biofouling in marine vehicles, or spreading in infectious tissue, etc.

Due to the interdisciplinary nature of my work, I envision a strong and active collaboration with fellow faculty in engineering and the basic sciences and/or work with them to setup specific techniques (such as constructing reporter strains, etc.) in my lab.

Selected Publications:

Srinivasan, S., Wei, Z., Mahadevan, L. (2016). Buckling instability in extensional flow of a thin non-uniformly viscous sheet. (under review)

Wang, X., Koehler, S. A., Wilking, J. N., Sinha, N. N., Cabeen, M. T., Srinivasan, S., … others. (2016). Probing phenotypic growth in expanding Bacillus subtilis biofilms. Applied Microbiology and Biotechnology, 100(10), 4607–4615.

Srinivasan, S., Kleingartner, J. A., Gilbert, J. B., Cohen, R. E., Milne, A. J. B., & McKinley, G. H. (2015). Sustainable drag reduction in turbulent Taylor-Couette flows by depositing sprayable superhydrophobic surfaces. Physical Review Letters, 114(1), 14501.

Kleingartner, J. A*., Srinivasan, S.*, Truong, Q. T., Sieber, M., Cohen, R. E., & McKinley, G. H. (2015). Designing Robust Hierarchically Textured Oleophobic Fabrics. Langmuir, 31(48), 13201–13213.

Srinivasan, S., Chhatre, S. S., Guardado, J. O., Park, K.-C., Parker, A. R., Rubner, M. F., Mckinley, G.H, Cohen, R. E. (2014). Quantification of feather structure, wettability and resistance to liquid penetration. Journal of The Royal Society Interface, 11(96), 20140287.

Srinivasan, S., Choi, W., Park, K.-C., Cohen, R. E., & McKinley, G. H. (2013). Drag reduction for viscous laminar flow on spray-coated non-wetting surfaces. Soft Matter, 9(24), 5691–5702. (featured on cover)

Srinivasan, S., Chhatre, S. S., Mabry, J. M., Cohen, R. E., & McKinley, G. H. (2011). Solution spraying of poly (methyl methacrylate) blends to fabricate microtextured, superoleophobic surfaces. Polymer, 52(14), 3209–3218.

Srinivasan, S., McKinley, G. H., & Cohen, R. E. (2011). Assessing the accuracy of contact angle measurements for sessile drops on liquid-repellent surfaces. Langmuir, 27(22), 13582–13589.