Table of Contents

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

This dataset includes flow cytometry measurements from HHQ experiments conducted during the MesoHux mesocosm experiment, May 2017, Bergen, Norway. Microbial mesocosms were spiked with 2-heptyl-4-quinolone (HHQ).

Triplicate 5 mL samples were preserved for flow cytometry with 0.5% glutaraldehyde (final concentration), incubated at 4°C for 10 min and frozen (-80°C) until analysis (within 2-3 weeks; Kemp et al. 1993). To calculate phytoplankton group abundances, 200 µl aliquots of fixed sample were added to a 96-well plate and run on a Guava flow cytometer (Millipore). Filtered seawater (0.45 µm) was run as a blank and instrument-specific beads were used to calibrate the cytometer. Samples were analyzed at low flow rate (0.24 µl s-1) for 3 min. Three major phytoplankton groups were distinguishable based on plots of forward scatter vs. orange (phycoerythrin-containing, Synechococcus spp.) or red (pico- and nanoeukaryotes) fluorescence signals (Worden and Binder 2003). 

Samples for enumerating bacteria were stained prior to running on the Guava in 0.5% v/v SybrGreen I DNA stain for 1 hour at room temperature in the dark.

Mesocosm treatment for all HHQ experiments was as follows:
Redfield: N:P added in a 16:1 ratio during the first 3 days of the experiment, no shading

HHQ treatments here are as follows:
High HHQ - 100 ng mL-1 (410 uM) added to triplicate 5L bottles.
DMSO control - equivalent (v:v) DMSO added to triplicate 5L bottles.

 All bottles were incubated for 24h in a flow-through tank, that was shaded to mimic in situ conditions. Chlorophyll samples were taken at T0 and T24 for all experiments.

Data were processed in Excel with statistics run in Excel, R, or Matlab.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions

NSF Award Abstract:
Bacteria and phytoplankton play a central role in the modification and flow of materials and nutrients through the marine environment. While it has been established that interactions between these two domains are complex, the mechanisms that underpin these interactions remain largely unknown. There is increasing recognition, however, that dissolved chemical cues govern these microbial interactions. This project focuses on establishing a mechanistic framework for how bacterially derived signaling molecules influence interactions between phytoplankton and bacteria. The quorum-sensing (QS) molecule, 2-heptyl-4-quinolone (HHQ) will be used as a model compound for these investigations. Previously published work suggests that exposure to very low levels of HHQ results in phytoplankton mortality. Gaining a mechanistic understanding of these ecologically important interactions will help to inform mathematical models for the accurate prediction of the cycling of material through the marine microbial loop. This work initiates a new, hybrid workshop-internship undergraduate research program in chemical ecology, with a focus

Bacteria and phytoplankton play a central role in the modification and flow of materials and nutrients through the marine environment. While it has been established that interactions between these two domains are complex, the mechanisms that underpin these interactions remain largely unknown. There is increasing recognition, however, that dissolved chemical cues govern these microbial interactions. This project focuses on establishing a mechanistic framework for how bacterially derived signaling molecules influence interactions between phytoplankton and bacteria. The quorum-sensing (QS) molecule, 2-heptyl-4-quinolone (HHQ) will be used as a model compound for these investigations. Previously published work suggests that exposure to very low levels of HHQ results in phytoplankton mortality. Gaining a mechanistic understanding of these ecologically important interactions will help to inform mathematical models for the accurate prediction of the cycling of material through the marine microbial loop. This work initiates a new, hybrid workshop-internship undergraduate research program in chemical ecology, with a focus into bacteria-phytoplankton interactions. Undergraduate students participate in an intense summer learning experience where research and field-based exercises are supplemented with short-lecture based modules. Students return to their home institutions and work closely with the PIs to conduct interdisciplinary research relating to the aims and scope of the summer research. This research also provides training and career development to two graduate students and a postdoctoral scientist.

Interactions between phytoplankton and bacteria play a central role in mediating biogeochemical cycling and microbial trophic structure in the ocean. The intricate relationships between these two domains of life are mediated via excreted molecules that facilitate communication and determine competitive outcomes. Despite their predicted importance, identifying these released compounds has remained a challenge. The PIs recently identified a bacterial QS molecule, HHQ, produced by globally distributed marine gamma-proteobacteria, which induces phytoplankton mortality. The PIs therefore hypothesize that bacteria QS signals are critical drivers of phytoplankton population dynamics and, ultimately, biogeochemical fluxes. This project investigates the timing and magnitude of HHQ production, and the physiological and transcriptomic responses of susceptible phytoplankton species to HHQ exposure, and quantifies the influence of HHQ on natural algal and bacterial assemblages. The work connects laboratory and field-based experiments to understand the governance of chemical signaling on marine microbial interactions, and has the potential to yield broadly applicable insights into how microbial interactions influence biogeochemical fluxes in the marine environment.