The production of extracellular polymeric substances (EPS) by planktonic microbes can influence the fate of oil and chemical dispersants in the ocean through emulsification, degradation, dispersion, aggregation, and/or sedimentation. In turn, microbial community structure and function, including the production and character of EPS, is influenced by the concentration and chemical composition of oil and chemical dispersants. For example, the production of marine oil snow and its sedimentation and flocculent accumulation to the seafloor were observed on an expansive scale after the Deepwater Horizon oil spill in the Northern Gulf of Mexico in 2010, but little is known about the underlying control of these processes. Here, we review what we do know about microbially produced EPS, how oil and chemical dispersant can influence the production rate and chemical and physical properties of EPS, and ultimately the fate of oil in the water column. To improve our response to future oil spills, we need a better understanding of the biological and physiochemical controls of EPS production by microbes under a range of environmental conditions, and in this paper, we provide the key knowledge gaps that need to be filled to do so. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Scientific Significance StatementExtracellular polymeric substances (EPS) are a group of chemically heterogeneous polymers released into the environment by microbes (bacteria, archaea, and phytoplankton), often in response to environmental stresses. EPS serve an important role in determining the fate and transport of oil after a spill, but relatively little is known about EPS production in relation to oil and dispersants, especially at molecular and chemical levels. Here, we summarize the scope of our current knowledge and identify major knowledge gaps. 3Limnology and Oceanography Letters 1, 2016, 3-26

The hydroxyl radical ( • OH) is the most reactive oxidant produced in natural waters. Photoproduction by chromophoric dissolved organic matter (CDOM) is one of its main sources, but the structures responsible for this production remain unknown. Here, a series of substituted phenol model compounds are examined to test whether these structures could act as a source of • OH. We find that many of these compounds do produce • OH with quantum yields (Φ) ranging from ∼10 −4 to ∼10 −2 . In particular, two compounds that have hydroxy groups and carboxyl groups in a para relationship (4-hydroxybenzoic acid and 2,4-dihydroxybenzoic acid) exhibit relatively high Φ values, ∼10 −2 . For 2,4-dihydroxybenzoic acid, the formation of • OH was confirmed through the use of competition kinetics and reaction with methane. We conclude that these types of structures, which may derive from polyphenolic source materials such as lignins, tannins, and humic substances, could be an important source of • OH in natural waters.

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