Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

This dataset includes MCAMUF (glucosidase and peptidase) hydrolysis rates to measure microbial enzyme activities on particles collected from gravity filtered seawater. Samples were collected on RV/Sonne cruise SO248 in May 2016. Links to archived CTD data are also provided.

Water was collected via Niskin bottles mounted on a rosette, equipped with a CTD.

Experiments on (operationally defined) particles were carried out by gravity-filtering water through 3 µm pore size filters.  1/12th sections of the 3 µm pore-size filters were submerged in 4 mL artificial seawater in incubation cuvettes.  Particle-associated peptidase and glucosidase activity assays were set up in 4 mL cuvettes. For live duplicate incubations, two particle-containing filter pieces (each 1/12th of entire filter) were separately submerged in 4 mL of cooled, autoclaved ambient seawater. A single killed control was prepared by submerging a sterile filter piece (1/12th of unused filter) in 4 mL of cooled, autoclaved ambient seawater. Substrates were added to a final concentration of 100 µM. At various timepoints—upon addition of substrate (to), 24 h (t1), 48 (t2), and 72 h (t3)—live duplicates and killed control singleton were subsampled by taking 3 x 200 uL (for technical triplicates) per incubation, and placed in a 96 well plate for fluorescence measurement using the Tecan Plate Reader. Fluorescence values were converted to hydrolysis rates using calibration curves with the MCA and MUF fluorophores, and were  normalized by the volume of filtrate that passed through the 3 µm filter. Two substrates, -glucose and -glucose linked to a 4-methylumbelliferyl (MUF) fluorophore, were used to measure glucosidase activities. Five substrates linked to a 7-amido-4-methyl coumarin (MCA) fluorophore, one amino acid – leucine – and four oligopeptides – the chymotrypsin substrates alanine-alanine-phenylalanine (AAF) and alanine-alanine-proline-phenylalanine (AAPF), and the trypsin substrates glutamine-alanine-arginine (QAR) and phenylalanine-serine-arginine (FSR) – were used to measure exo- and endo-acting peptidase activities, respectively. Hydrolysis rates of the substrates were measured as an increase in fluorescence as the fluorophore was hydrolyzed from the substrate over time [as in Hoppe, 1993; Obayashi and Suzuki, 2005].

a-glu = substrate to measure alpha glucosidase: 4-methylumbelliferyl-a-D-glucopyranoside
b-glu = substrate to measure beta glucosidase: 4-methylumbelliferyl-ß-D-glucopyranoside
L = substrate to measure leucine aminopeptidase (L-leucine-7-amido-4 MCA)
AAF = substrate to measure chymotrypsin activity: ala-ala-phe-MCA
AAPF = substrate to measure chymotrypsin activity: N-succinyl-ala-ala-pro-phe-MCA
QAR = substrate to measure trypsin activity: Boc-gln-ala-arg-MCA  
FSR = substrate to measure trypsin activity: N-t-boc-phe-ser-arg-MCA 

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- reduced decimal precision of rate columns from 9 to 6 places; time_elapsed from 7 to 0 places

NSF Award Abstract:
Heterotrophic microbial communities are key players in the marine carbon cycle, transforming and respiring organic carbon, regenerating nutrients, and acting as the final filter in sediments through which organic matter passes before long-term burial. Microbially-driven carbon cycling in the ocean profoundly affects the global carbon cycle, but key factors determining rates and locations of organic matter remineralization are unclear. In this study, researchers from the University of North Carolina at Chapel Hill will investigate the ability of pelagic microbial communities to initiate the remineralization of polysaccharides and proteins, which together constitute a major pool of organic matter in the ocean. Results from this study will be predictive on a large scale regarding the nature of the microbial response to organic matter input, and will provide a mechanistic framework for interpreting organic matter reactivity in the ocean.

Broader Impacts: This study will provide scientific training for undergraduate and graduate students from underrepresented groups. The project will also involve German colleagues, thus strengthening international scientific collaboration.