Path to “dirty blizzard” from Deepwater Horizon deep-sea plume: Bacteria form streamers on rising oil droplets to increase drag.

During the Deepwater Horizon oil spill, wellhead injection of dispersant caused a large pool of micro-droplets to be entrained in the 400 m thick deep-sea plume spanning over kilometers. The perceived fates of these droplets are metabolic degradation or sedimentation. However, both fates are contested on the grounds that droplets rise too fast to allow microbes to encounter, adhere, and grow over them to initiate biotic processes. Using a microfluidic platform capable of investigating a single oil droplet rising through a microbial suspension at ecologically relevant length (0.5um–1 mm) and time scales (1 ms–1 d) with well-controlled physicochemical environments, we found that within minutes after droplet's exposure to Pseudomonas suspensions, long polymeric streamers are extruded behind it and bundled into a large tail extending up to 10 drop diameters within hours. Flow measurements show that drag is increased by > 60% with only a few streamers. Increase in drag by streamers slows the drop and consequently lengthens its residence time to surrounding microbes. Short formation time scales compounded with impacts on hydrodynamics provide a creditable missing link in pathways to biodegradation and sedimentation, and significant implications in droplet transport models.