Abstract
Biofilm-sediment aggregate (BSA) contains a high water content, either within internal pores and channels or bound by extracellular polymeric substances (EPS) forming a highly hydrated biofilm matrix. Desiccation of BSAs alters the biofilm morphology and thus the physical characteristics of porous media, such as the binding matrix within BSA and internal pore geometry. Observing BSAs in their naturally hydrated form is essential but hampered due to the lack of techniques for imaging and discerning hydrated materials. Generally, imagery techniques (scanning electron microscopy (SEM), transmission electron microscopy (TEM), and focused ion beam nanotomography (FIB-nt)) involve the desiccation of BSAs (freeze-drying or acetone dehydration) or prevent differentiation between BSA components such as inorganic particles and pore water (confocal laser scanning microscopic (CLSM)). Here, we propose a novel methodology that simultaneously achieves the 3D visualization and quantification of BSAs and their components in their hydrated form at a submicron resolution using X-ray microcomputed tomography (μ-CT). It enables the high-resolution detection of comparable morphology of multiphase components within a hydrated aggregate: each single inorganic particle and the hydrated biofilm matrix. This allows the estimation of aggregate density and the illustration of biofilm-sediment binding matrix. This information provides valuable insights into investigations of the transport of BSAs and aggregate-associated sediment particles, contaminants (such as microplastics), organic carbon, and their impacts on aquatic biogeochemical cycling.
Highlights
Sediment particles in aquatic environments provide suitable solid−liquid interfaces for microorganism accumulation.[1]
The internal structure of Biofilm-sediment aggregate (BSA) is critical to the physical transport of BSAs and associated materials, often accelerating the deposition of suspended particulate matter (SPM)[10] and strengthening the resuspension resistance of benthic deposits.[11,12]
Fractal theory has been applied to study aggregate structure,[16−18] assuming a self-similar structure that self-repeats at all dimensional scales.[19]. This is due to a lack of currently available techniques to validate the internal structure of BSAs
Summary
Sediment particles in aquatic environments provide suitable solid−liquid interfaces for microorganism (e.g., bacteria, algae, diatom, fungi, and archaea) accumulation.[1] By secreting copious amounts of extracellular polymeric substances (EPS) binding sometimes more than 90% water[2,3] and adhering sediment particles together, these microorganisms form hydrogel-like microorganism-sediment aggregates, defined here as “biofilmsediment aggregates” (BSAs). The porosity, permeability, or density cannot be directly measured but instead are estimated by Stokes’ law, Received: July 27, 2018 Revised: October 16, 2018 Accepted: October 24, 2018 Published: October 24, 2018
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