(408i) Microbially-Induced Emulsification of Hexadecane By Marinobacter sp17

Microbes strongly affect the transport and fate of non-aqueous phase liquids (NAPLs) in aquatic ecosystems via the intrinsically coupled processes of bioemulsification and biodegradation^[1]. In the presence of a NAPL, many microbial species synthesize and release biosurfactants (amphiphilic biomolecules like rhamnolipids) that partition to the NAPL-water interface and, either spontaneously or in synergy with flow, disperse one liquid into the other. The occurrence of NAPL-in-water or water-in-NAPL emulsions depends mainly on the molecular structure of the biosurfactants as well as on the local volume fractions, transport properties and exact chemical composition of the aqueous and non-aqueous phases. If the NAPL is also biodegradable, then the microbes form biofilm communities over the NAPL-water interface. Bioemulsification and biodegradation are encountered in important natural phenomena and applications, including the dispersion of crude oil in the sea, the migration of NAPL plumes in the subsurface, and the fermentation of oils in bioreactors.

In this work, the bioemulsification of hexadecane (model NAPL) by the halotolerant microbes Marinobacter sp17 is experimentally investigated in batch and microfluidic microcosms. In batch microcosms, these microbes exhibit the ability to transform a layer of hexadecane, initially floating over seawater, to a highly polydisperse oil-in-water emulsion. The evolution of the droplet size distribution is followed by microscopic image analysis and dynamic light scattering measurements and is found to be multimodal with peaks over a range spanning from hundreds of nanometers up to several millimeters. Over the course of weeks, the average droplet diameter is reduced by the combined effects of biodegradation and accumulating emulsification capacity. The droplet shrinking that is caused by biodegradation alone, is also determined for individual hexadecane droplets using a custom-made microfluidic device and phase-contrast microscopy. Moreover, the structure of the microbial biofilms that coat and degrade hexadecane droplets is visualized and quantified with confocal microscopic imaging. Experimental results are discussed in conjunction with predictions from pertinent theoretical models^[2].

Acknowledgement
This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 741799 (project "OILY MICROCOSM").

References
[1] Kapellos GE. (2017) "Microbial strategies for oil biodegradation", In Modeling of Microscale Transport in Biological Processes; Becker, S.M., Ed.; Academic Press, pp. 19-39.

[2] Kapellos GE, Paraskeva CA, Kalogerakis N, Doyle PS. (2018). Bioengineering, 5:15.