Water was collected via Niskin bottles mounted on a rosette, equipped with a CTD.
The potential of the seawater microbial community to hydrolyze six high-molecular-weight polysaccharides (arabinogalactan, chondroitin sulfate, fucoidan, laminarin, pullulan, and xylan) was investigated in surface and bottom water. For each substrate, three 15 mL falcon tubes were filled with seawater and one 15 mL falcon tube was filled with autoclaved seawater to serve as a killed control. Substrate was added at 3.5 uM monomer-equivalent concentrations. Two 15 mL falcon tubes – one with seawater and one with autoclaved seawater – with no added substrate served as blank controls. Incubations were stored in the dark at 0 C. Subsamples of the incubations were collected at time zero, and at 120h, 240 h, 360 h, and 600 h. At each timepoint, 2 mL of seawater was collected from the 15 mL falcon tube using a sterile syringe, filtered through a 0.2 um pore size syringe filter, and stored frozen until processing.
The hydrolysis of high molecular weight substrate to lower molecular weight hydrolysis products was measured using gel permeation chromatography with fluorescence detection, after the method of Arnosti [1996, 2003]. In short, the subsample was injected onto a series of columns consisting of a 21 cm column of G50 and a 19 cm column of G75 Sephadex gel. The fluorescence of the column effluent was measured at excitation and emission wavelengths of 490 and 530 nm, respectively. Hydrolysis rates were calculated from the change in molecular weight distribution of the substrate over time, as described in detail in Arnosti [2003].
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