Abstract:
Measurements of surface tension in the EPS colloidal size fraction in seawater samples from mesocosms and comparison to protein to polysaccharide ratios. Surface tension, pH measurements of colloidal EPS and model EPS components. Concentrations of the colloidal EPS proteins, neutral sugars, and uronic acids.
Suggested Citation:
Kathy Schwehr, Chen Xu, Saijin Zhang, Morgan Beaver, Cameron Jackson, Oscar Agueda, Charles Bergen. 2018. Surface tension of exopolymeric substances in seawater in the presence or absence of oil and/or Corexit. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N79W0D1K
Purpose:
To compare the surface tension changes in the colloidal EPS in different treatments (control, with oil, with oil + Corexit) with the colloidal EPS chemical compositional changes in protein and polysaccharides, and the mass balance of organic carbon in size fractions. To provide insight into the biopolymer self-assembly as micelles or aggregates by exploring the surface tension behavior of model EPS components.
Data Parameters and Units:
Sample (WAF, DCEWAF, or CEWAF) Sft = surface tension in mN/m Temperature of sample or solution during sft measurement in deg C CHO = neutral sugars in mg/L URA = uronic acids in mg/L Protein = proteins in mg/L BSA = bovine serum albumin protein in mg/L COC = colloidal organic carbon in mg/L (0.45um >COC>3 kDa) DOC = dissolved organic carbon in mg/L (0.45um >DOC) Truly dissolved organic carbon in mg/L (truly dissolved < 3 kDa) Colloidal EPS = colloidal extracellular polymeric substances (>0.45um and >3 kDa) DOC = dissolved (0.45um >DOC) Truly dissolved (truly dissolved < 3 kDa) Concentration (mg/L) pH Glucuronic acid concentration (mg/L) A, B, C = replicates Control = seawater WAF = water accommodated fraction, oil:seawater is 1:4000 CEWAF = chemically enhanced WAF with Corexit dispersant, Corexit: WAF is 1:20 DCEWAF = diluted CEWAF, 10x diluted CEWAF -99.99 or any negative number indicates no data available
Methods:
Methods for the mesocosms are provided in the following datasets: Coastal seawater amended with microbial concentrate; COAST, http://doi.org/10.7266/N7PK0D64; Gulf of Mexico open ocean amended with nutrients; GOMOO, http://doi.org/10.7266/N78P5XZD; and Gulf of Mexico coastal seawater amended with nutrients; GOMCOAST, http://doi.org/10.7266/N74X568X. Extraction of EPS colloidal fraction Briefly, for this study, a sample aliquot from the water column was filtered through a 0.45 µm flipmate device to remove particles. The filtrate was then processed in a 3 kDa ultra centrifugal membrane to collect the colloidal (retentate) fraction. The retentate was collected and rinsed three times with 18 MΩ –cm until the final volume was concentrated at least 25-fold. This EPS colloids fraction from the water column, < 0.45 µm and > 3 kDa, was then used for most measurements mentioned in this work. Each EPS colloidal sample was measured for protein and polysaccharides as total carbohydrates as described below, and diluted with the permeate from the Control treatment for measurement of SFT to maintain ionic composition of the original mesocosm sample. Dilutions of the concentrated EPS colloidal fraction were made such that the surface tension of samples was < the surface tension of the 3 kDa permeate for the Control, +/- 2%. So the solution used for the coastal waters that were amended with microbial concentrate was concentrated 8.3x; 25x concentrated in the ocean waters; not concentrated in the coastal waters amended with nutrients. Colloidal fractions were obtained for different replicates. Replicate is indicated with letter (A, B, C). Estimated oil equivalents,PAH concentration, and nutrient composition for these replicates is available in GRIIDC dataset R4.x263.000:0019 "Oil Composition and nutrients for the COAST mesocosm study, COASTal water with added coastal microbial concentrate" Experiments with standard biomacromolecules In order to assess the effects of proteins and polysaccharides (alone or in combination) on SFT, experiments were conducted in artificial seawater, ASW, using Bovine Serum Albumin (BSA), which has a isoelectric point, pI, of 4.7- 5.4 (depending on conditions), and Glucuronic acid, a major component of alginic acid and an abundant component of EPS, which has a pKa of 2.8-3.2 (depending on configuration). In the ASW with a pH of ~8, these moieties would be deprotonated which would enhance their surface reactivity. Surface tension The surface tension of the samples were taken when the control and WAF treatments appeared to have reached an equilibrium status with no further marine snow production. This occurred at different times for the different mesocosm experiments, i.e., for the open ocean conditions on day 4, amended with nutrients; and the 2 coastal waters, day 3, amended with microbial concentrate; day 4, amended with nutrients. SFT was measured using a Kibron EZ Pi-Plus tensiometer, which employed the Du Nouy-Paddy technique combined with a 0.5 mm diameter probe (Padday et al. 1974). The probe was metal alloyed with a hydrophilic oxide permitting a negligible contact with samples. The 1.5 mL sample in a polypropylene cuvette, was kept at constant temperature 22.5 + 0.3 °C using a recirculating water bath. The probe was cleaned between samples by combustion with a butane torch. Each sample was measured a minimum of four times with replicate measurements displaying a relative standard deviation (RSD) of ≤5%. The instrument was calibrated against 18.2 MΩ –cm resistivity Type I water. Protein and Polysaccharide determination Protein content in EPS was measured based on a modified bicinchoninic acid method (Smith et al., 1985) using the Pierce protein assay kit, with BSA as the standard. Polysaccharide concentration was determined using the anthrone method (Morris, 1948), with glucose as the standard. Uronic acid was estimated by adding sodium borate (75 mM) in concentrated sulfuric acid and m-hydroxydiphenyl, with glucuronic acid as the standard (Hung and Santschi, 2001). The sum of proteins, polysaccharides and uronic acids, was expressed as the sum of BSA, glucose and glucuronic acid equivalents, with respect to dissolved organic carbon. EPS composition and concentrations were calculated from samples that were collected from three replicate mesocosm tanks of each treatment. Dissolved Organic Carbon determination Concentrations of DOC were measured on a Shimadzu TOC-L analyzer using a high temperature combustion method. Sample filtrate from 0.7 um pre-combusted Whatman GFF membranes were acidified to < pH 2 with 2N HCl solution then purged with pure air for 10 min to remove inorganic carbon. The sample was then combusted at 680°C and subjected to CO2 measurement to determine the amount of carbon. To calculate the DOC concentration, system blanks were subtracted and calculated against a calibration curve using potassium hydroxyphthalate as a standard. Samples whose fluctuation factor exceeded 3% were measured three times and the average of the two values giving the lowest fluctuation factor was adopted.
Provenance and Historical References:
Padday, J.F., Pitt, A.R., and R.M. Pashley (1974). Menisci at a free liquid surface: surface tension from the maximum pull on a rod. J. Chem. Soc., Faraday Trans. 1, 71: 1919-1931. doi: 10.1039/F19757101919 Smith, P.K., Krohn, R.I, Hermanson, G.T., Mallia, A.K., Gartner, F.H., Provenzano, M.D., Fujimoto, E.K., Goeke, N.M., Olson, B.J., and D.C. Klenk (1985). Measurement of protein using bicinchoninic acid. Analytical Biochemistry, 150(1): 76-85. doi: 10.1016/0003-2697(85)90442-7 Morris, D.L. (1948). Quantitative Determination of Carbohydrates with Dreywood's Anthrone Reagent. Science, 107(2775): 254-255. Hung, C. and Santschi, P.H. (2001). Spectrophotometric determination of total uronic acids in seawater using cation-exchange separation and pre-concentration by lyophilization. Analytica Chimica Acta, 427(1): 111-117. doi: 10.1016/S0003-2670(00)01196-X
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