Interplay of chemical and thermal gradient on bacterial migration in a diffusive microfluidic device

Abstract

Living systems are constantly under different combinations of competing gradients of chemical, thermal, pH, and mechanical stresses allied. The present work is about competing chemical and thermal gradients imposed on in a diffusive stagnant microfluidic environment. The bacterial cells were exposed to opposing and aligned gradients of an attractant (1 mM sorbitol) or a repellant (1 mM NiSO) and temperature. The effects of the repellant/attractant and temperature on migration behavior, migration rate, and initiation time for migration have been reported. It has been observed that under competing gradients of an attractant and temperature, the nutrient gradient (gradient generated by cells itself) initiates directed migration, which, in turn, is influenced by temperature through the metabolic rate. Exposure to competing gradients of an inhibitor and temperature leads to the imposed chemical gradient governing the directed cell migration. The cells under opposing gradients of the repellant and temperature have experienced the longest decision time (∼60 min). The conclusion is that in a competing chemical and thermal gradient environment in the range of experimental conditions used in the present work, the migration of is always initiated and governed by chemical gradients (either generated by the cells or imposed upon externally), but the migration rate and percentage of migration of cells are influenced by temperature, shedding insights into the importance of such gradients in deciding collective dynamics of such cells in physiological conditions.

Microfluidic techniques for separation of bacterial cells via taxis

“…Microfluidics can also provide greater control to generate precise and stable gradients of stimuli such as chemical, temperature and pH, which in turn allows more precise studies into bacterial taxis [22]. Also, microfluidics enables easier studies of more than one environmental condition such as chemical and temperature gradients simultaneously [23].…”

“…A microfluidic device was fabricated to create temperature and chemical gradients simultaneously (Fig. 7) [23]. The effect of gold nanoparticles on bacterial thermotaxis and chemotaxis was studied using this device in order to determine antibacterial properties of gold nanoparticles [50].…”

Microfluidic Devices Developed for and Inspired by Thermotaxis and Chemotaxis

“…As an example of the chemotaxis of bacteria, Murugesan and his collaborators fabricated a microfluidic device to analyze the simultaneous effect of thermal and chemical gradients on the migration of E. coli [ 16 ]. As shown in Figure 6 , there are side channels for hot and cold water to generate a longitudinal thermal gradient along the experiment chamber.…”

“… A microfluidic chip developed by Murugesan et al, which combines thermal and chemical gradients in a single chip to perform both thermotaxis and chemotaxis on E. coli bacteria at the same time. Reproduced from [ 16 ]. …”

“…Thermotactic response is their defensive mechanism to migrate toward the desired temperature and avoid temperatures that trigger undesired reactions in them, causing damage or death. The thermotaxis behavior of several different cells and microorganisms has been analyzed so far, among which spermatozoon [ 14 ], Caenorhabditis elegans or C. elegans (from the family of nematodes) [ 15 ] and Escherichia coli or E. coli (from the family of bacteria) [ 16 ] have been the most common due to their sensitive response and vast applications. Figure 1 shows what these organisms look like.…”