講演者： Andrew S. Utada 氏(筑波大学)
タイトル：Bacteria on High Fat Diets Cooperate to Stay Fit
Obligately hydrocarbonoclastic bacteria (OHCB) are cosmopolitan marine bacteria that can survive by consuming hydrocarbons as a sole energy and carbon source. In the ocean, these bacteria are typically found at very low densities but bloom to become the dominant bacteria at the site of oil spills. These organisms have likely evolved to directly utilize the abundant hydrocarbons in the marine environment as part of the cryptic carbon cycle and around natural oil-seeps on the sea floor. They are thought to degrade a significant amount of the worldwide spilled oil, which is why they have been organisms of interest for use as agents of bioremediation.
Alcanivorax borkumensis was the first OHCB sequenced in the mid-2000s. Like most bacteria, it is thought to transition between planktonic and biofilm states. Biofilms are 3D communities of densely packed bacteria encased in a self-secreted matrix of extracellular polymeric substances (EPS) that both protect and help the community remain attached to a surface. However, unlike most environmental bacteria, which typically absorb their carbon (and energy) directly from nutrients in the surrounding water, A. borkumensis biofilms must form on the oil-water interface. Although formation of a biofilm at fluid-fluid interface is not unique and, in some ways, shares some similarity to pellicle formation at the air-liquid interface, the similarities diverge there. Biofilms can generate gradients in the nutrients between the internal and external environments. In the case of an A. borkumensis biofilm surrounding an oil droplet, only the cells at the interface have access to the carbon/energy, while the outward facing cells have access to micronutrients. It is not clear how the obvious nutrient gradients and the fluid interface affects A. borkumensis biofilm formation.
Due to the difficulty in tracking individual droplets over time, biofilm dynamics of this interesting organism have largely been conducted though bulk methods. From an applied ecology perspective, clarifying the microscopic mechanisms of biofilm formation for this and similar OHCB organism may reveal features to be exploited in the management of oil spills in the natural environment. From the active-matter physics perspective, the behavior of self-driven layer at a phase-separated interface of may reveal new physics.
We introduce a microfluidic platform that can trap and store oil microdroplets for weeks. This platform greatly facilitates imaging and analysis of biofilm formation at the oil-water interface. We demonstrate unresolved biofilm dynamics by A. borkumensis, showing its ability to rapidly shred oil drops. We analyze various physical aspects of this organism and correlate them to its ability to align and cooperate at the interface to drive a rapid and large-scale remodeling of the interface. This remodeling appears to be the most egalitarian and efficient distribution of resources.