Evaporation-Induced Patterns from Droplets Containing Motile and Nonmotile Bacteria

Abstract

In this letter, we report the observations of specific pattern formation from the evaporation of aqueous droplets containing motile and nonmotile bacteria. We found that when motile bacteria were present the droplet evaporated into disclike patterned deposits of bacteria. However, when the bacteria were made nonmotile by treatment with liquid nitrogen, the droplet evaporated into ringlike deposits. We also observed that bacteria with higher motility produced more uniformly deposited disclike patterns. Furthermore, we propose a model with numerical simulations to explain the mechanism of formation of these patterns. The model is based on the advective fluid flow from the center of the droplet toward the edge due to enhanced evaporation from the edge of the pinned droplet in comparison to that from the free surface. For the case of motile bacteria, we have added another velocity parameter toward the axis of the droplet and directed against the fluid flow in order to account for the disclike pattern formation. The numerical simulations match the experimental observations well. The present work, by qualitative and quantitative understanding of the evaporation of bacteria droplets, demonstrates that the inherent bacterial motility is primarily responsible for the formation of these differential patterns.

Auto-production of biosurfactants reverses the coffee ring effect in a bacterial system

“…No coffee ring pattern was observed for any of the surfactant concentrations studied here (0.1–1.5% w/v). This extends previous work where only minor inhibition of the coffee ring effect9 or only a strong central accumulation8 was obtained.…”

“…Our observations suggest that the mutant bacteria were subject to the capillary flow, whereas the wild-type bacteria gave a nearly uniform distribution of bacteria after drying due to the production of the biosurfactant rhamnolipid, which counteracted this flow. Our results show an improvement over previous reported attempts to obtain homogeneous depositions in droplets89.…”

Interdisciplinary engineering approaches to study how pathogenic bacteria interact with fresh produce

“…Bacteria with exposure to resources will outgrow other bacteria while the density of the initial distribution will play a role in determining interactions. The deposition patterns of bacteria from a sessile drop is not trivial though and depends on several parameters such as size of each bacterium, motility, and rate of drying (Shen et al, 2010;Nellimoottil et al, 2007). Nellimoottil et al (2007) studied the effects of motility in droplet drying using an analytical solution for the velocity profile inside the droplet.…”

“…The deposition patterns of bacteria from a sessile drop is not trivial though and depends on several parameters such as size of each bacterium, motility, and rate of drying (Shen et al, 2010;Nellimoottil et al, 2007). Nellimoottil et al (2007) studied the effects of motility in droplet drying using an analytical solution for the velocity profile inside the droplet. They found motile bacteria formed a uniform disklike pattern while non-motile bacteria formed a more ringlike pattern.…”

Deposition of Coatings from Live Yeast Cells and Large Particles by “Convective-Sedimentation” Assembly

“…Most of the cell deposition techniques reported involve patterning, electrodes or templating. Such methods include the use of electroactive substrates,22 dielectrophoresis between microelectrodes,21 modulated magnetic fields,23 inkjet and laser printing,24,25 optical trapping,26 biologically-friendly lithography,27-29 covalent bonding to alkanethiols,30 encapsulation with a polyelectrolyte,31 laminar flow patterning32 and droplet templating 33. Several methods use polydimethylsiloxane (PDMS) to pattern substrates for cell growth 34-37.…”