Microbial Extracellular Polymeric Substances (EPSs) in Ocean Systems

Abstract

Microbial cells (i.e., bacteria, archaea, microeukaryotes) in oceans secrete a diverse array of large molecules, collectively called extracellular polymeric substances (EPSs) or simply exopolymers. These secretions facilitate attachment to surfaces that lead to the formation of structured ‘biofilm’ communities. In open-water environments, they also lead to formation of organic colloids, and larger aggregations of cells, called ‘marine snow.’ Secretion of EPS is now recognized as a fundamental microbial adaptation, occurring under many environmental conditions, and one that influences many ocean processes. This relatively recent realization has revolutionized our understanding of microbial impacts on ocean systems. EPS occur in a range of molecular sizes, conformations and physical/chemical properties, and polysaccharides, proteins, lipids, and even nucleic acids are actively secreted components. Interestingly, however, the physical ultrastructure of how individual EPS interact with each other is poorly understood. Together, the EPS matrix molecules form a three-dimensional architecture from which cells may localize extracellular activities and conduct cooperative/antagonistic interactions that cannot be accomplished efficiently by free-living cells. EPS alter optical signatures of sediments and seawater, and are involved in biogeomineral precipitation and the construction of microbial macrostructures, and horizontal-transfers of genetic information. In the water-column, they contribute to the formation of marine snow, transparent exopolymer particles (TEPs), sea-surface microlayer biofilm, and marine oil snow. Excessive production of EPS occurs during later-stages of phytoplankton blooms as an excess metabolic by product and releases a carbon pool that transitions among dissolved-, colloidal-, and gel-states. Some EPS are highly labile carbon forms, while other forms appear quite refractory to degradation. Emerging studies suggest that EPS contribute to efficient trophic-transfer of environmental contaminants, and may provide a protective refugia for pathogenic cells within marine systems; one that enhances their survival/persistence. Finally, these secretions are prominent in ‘extreme’ environments ranging from sea-ice communities to hypersaline systems to the high-temperatures/pressures of hydrothermal-vent systems. This overview summarizes some of the roles of exopolymer in oceans.

Estuarine Dissolved Organic Carbon Flux From Space: With Application to Chesapeake and Delaware Bays

“…CDOM represents a portion of the bulk DOC pool, and earlier studies recognized the release of DOC by phytoplankton (e.g., Bjørrisen, ; Sharp, ). Many other studies addressed the DOC production by phytoplankton (Anderson & Williams, ; Decho & Gutierrez, ; Druon et al, ; Fisher et al, ; Mannino et al, , ; Rochelle‐Newall & Fisher, ). Both CB and DB are highly productive estuaries (Harding et al, ; Pennock & Sharp, ), so it is expected that phytoplankton blooms provide an important source of DOC to both bays.…”

“…There is a very large body of literature addressing the ability of phytoplankton to secrete DOC in the form of TEP (transparent exopolymeric material). An informative review is provided in Decho and Gutierrez (). Other important sources to these estuaries are lateral inputs from tidal wetlands (Axelrad et al, ; Jordan et al, ; Jordan & Correll, ; Roman & Dalber, ) and bottom sediments (Burdige & Homstead, ).…”

“…CDOM represents a portion of the bulk DOC pool, and earlier studies recognized the release of DOC by phytoplankton (e.g., Bjørrisen, 1988;Sharp, 1977). Many other studies addressed the DOC production by phytoplankton (Anderson & Williams, 1998;Decho & Gutierrez, 2017;Druon et al, 2010;Fisher et al, 1998;Mannino et al, 2008Mannino et al, , 2016Rochelle-Newall & Fisher, 2002).…”

Green Rust: The Simple Organizing &lsquo;Seed&rsquo; of All Life?&nbsp;&nbsp;<strong> </strong>

“…[28,258] Thus, the first palpable living communities, still at the hydrothermal mound, could have been biofilms, adherence then, as it is often now, provided by 'excess' amyloid, probably augmented with carboxylates. [259,260,261,262,263,264,265,266] These putative biofilms comprising 'minimal organic cells' may have resembled iron-bearing microbialites. [267] …”

An Approach to Modeling Biofilm Growth During the Flocculation of Suspended Cohesive Sediments

“…In open-water environments, the structured biofilm communities and the secretion of EPS are a microbial adaption for ocean systems (Decho & Gutierrez, 2017). Besides biofouling (e.g., Barton et al, 2008;Delauney et al, 2010;Kerr et al, 1998;Metosh-Dickey et al, 2004;Zobell & Allen, 1935), biofilms are significantly highlighted for their influences on ecosystem health such as food web support (e.g., Saint-Béat et al, 2014), carbon and nutrient cycling (e.g., Ziegler & Lyon, 2010), photosynthetic activities (e.g., Lefebvre et al, 2011), or in determining the fate of pollutants (e.g., Quigg et al, 2016).…”