Abstract
Advances in microfluidics technology has enabled many discoveries on microbial mechanisms and phenotypes owing to its exquisite controls over biological and chemical environments. However, emulating accurate ecologically relevant flow environments (e.g. microbes around a rising oil droplet) in microfluidics remains challenging. Here, we present a microfluidic platform, i.e. ecology-on-a-chip (eChip), that simulates environmental conditions around an oil droplet rising through ocean water as commonly occurred during a deep-sea oil spill or a natural seep, and enables detailed observations of microbe-oil interactions at scales relevant to marine ecology (i.e. spatial scales of individual bacterium in a dense suspension and temporal scales from milliseconds to weeks or months). Owing to the unique capabilities, we present unprecedented observations of polymeric microbial aggregates formed on rising oil droplets and their associated hydrodynamic impacts including flow fields and momentum budgets. Using the platform with Pseudomonas, Marinobacter, and Alcarnivorax, we have shown that polymeric aggregates formed by them present significant differences in morphology, growth rates, and hydrodynamic impacts. This platform enables us to investigate unexplored array of microbial interactions with oil drops.
Highlights
The interactions of active colloids with liquid-liquid interfaces has received increasing attentions across scientific disciplines and applications, especially, in the wake of Deepwater Horizon disaster
The microfluidic channel was designed to fulfill the following functions: (i) it must be capable of producing a single sub-millimeter oil droplet (e.g. 100 μm) on-chip; (ii) it must be capable of trapping the generated droplet in a location while preserving its circular shape, maintaining an oleophobic contact angle with the top and bottom channel walls, and closely emulating the hydrodynamics around a rising micro-droplet; and (iii) it must be able to withstand the long-term observation that lasts weeks
The disposable eChip consists of a polydimethylsiloxane (PDMS) microchannel bonded to a glass microscope slide with air plasma
Summary
The interactions of active colloids (e.g. motile microbes) with liquid-liquid interfaces (e.g. a rising oil droplet) has received increasing attentions across scientific disciplines (e.g. microscale transport, microbiology, and tissue engineering, etc.) and applications (e.g. drug delivery, biofouling prevention, and pharmaceuticals synthesis etc.), especially, in the wake of Deepwater Horizon disaster. These unprecedented phenomena raised debates on alternative fates (i.e. biodegradation and sedimentation) of these droplets instead of surfacing, and the underlying mechanisms Despite significant efforts, these questions remain unanswered and key processes unresolved, which highlights our lack of knowledge in complex oil-colloid interactions under varying mechanical, chemical and biological oceanic environments subject to a rising oil droplet (e.g. temperature, flow shear, microbes and their secretions). There are currently no suitable methods to trap an oil droplet on-chip while leaving suspended bacteria undisturbed to emulate the microecosystem around a rising oil droplet in the water column In this manuscript, we describe an experimental microcosm platform, namely ecology-on-a-chip (eChip), for studying microbial interactions with a rising oil droplet at ecologically relevant length and time scales. The eChip allows us to obtain high spatial (weeks at the resolution of 1 ms) observations and leads to previously unattainable insights of microbial behaviors at the oil-water interface
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
