Sampling in the Whalen and Harvey Labs is in full swing. Our day begins at 0600 when members of both labs set out in a small boat to the mesocosm platform to collect the necessary water in acid-washed plastic carboys for all of our in-lab experiments. This happens in rain or shine, and we always hope for sunning warm weather, which is not always the case as in Norway, as residents can expect over 200 days of rain.
The Whalen Lab needs 60L of seawater from nutrient “replete” bags alone to prepare for the experiments ahead. We are interested in the molecule 2-heptyl-4-quinolone or HHQ for short. What is so special about HHQ….well, it is a known bacterial quorum sensing molecule – it helps bacteria talk with each other. Bacteria use special molecules to signal to other bacteria in the environment to coordinate behaviors – like turn on virulence genes, make antibiotics, or bioluminesce. Bacteria are always “listening” for these molecules with cell-surface receptors by monitoring their chemical environment in order to track changes in their numbers so they call collectively change their strategy at a moment’s notice.
At low densities of bacteria, quorum sensing molecules, like HHQ, diffuse away in the seawater, and therefore, are present at concentrations below the threshold required for detection. However, when bacteria are extremely abundant, the cumulative production of HHQ leads to locally high concentrations of the molecule in the microhabitat, thereby enabling detection by the bacterial community and inaction of a coordinated response.
Up until now, HHQ was well known in the medical literature, having originally been discovered in the lungs of patients with severe bacterial infections. Here, HHQ can rapidly accumulate in the mucus surrounding bacterial cells and lead to the coordinated behavior including virulence factors necessary for a pathogenic lifestyle. Last year, we reported HHQ was present in cultures of marine bacteria, and were able to hunt down the genes responsible for this molecule’s production.
We now know that HHQ does more than function simply as a communication molecule or “infochemical”. When we expose phytoplankton like Emiliania huxleyi, to low concentrations of HHQ, like 1 parts per billion, something interesting happens. This species of phytoplankton stops growing when exposed to low concentrations of HHQ and goes into what in laymen’s terms could be called stasis. The phytoplankton cell neither grows nor dies. This carries on for about three days, when finally death occurs.
The Whalen and Harvey Labs are trying to understand how such a fundamental chemical used in bacterial communication might impact phytoplankton growth dynamics in the real world. That is where the Bergen Mesocosm’s come in. We have sufficient evidence for the effects of HHQ on individual species of phytoplankton, but we still don’t yet know how a community of phytoplankton and their bacterial buddies will respond in the presence of HHQ when we test this compound in the field. Our experiments for MesoHux2017 will address two general questions: (1) how does the bacterial community change during the course of E. huxleyi bloom in response to HHQ, and (2) how does phytoplankton physiology change at the molecular level in response to HHQ?
To accomplish these aims, the Whalen lab has set out a very ambitious schedule of sample prep to obtain both DNA from bacterial communities to monitor how the “players” change in response to HHQ; and RNA which will show us what genes are being transcribed in response to HHQ exposure and how phytoplankton respond to bacterial chemical stressors. This requires us to filter lots of seawater from the mesocosm in a 10 deg C (50 deg F) on filters that can collect the material we want – 1 micron filter to retain phytoplankton and a 0.2 micron filter to get all the bacteria.
Once we filter the water through special plastic filters, we pop these into special plastic tubes that can hold up to extreme cold conditions and drop them into our giant cryoshipper that can maintain a temperature of -120 deg Celsius for 50 days at a stretch. Back at Haverford College, both DNA and RNA will be isolated from filters and further processed to address the questions above.
Anna storing samples in liquid nitrogen
Members of the Whalen/Harvey Labs have been working non-stop since their arrived, and everyone is pitching in to make the most of our limited time in the fjord. To keep spirits up, members take turns making dinner for the group of 8 scientists. We decided as a group to make a cake as a treat for celebrating our current sampling successes. Little did we know that the language barrier would be just an impediment to making a cake. For example. We thought we bought cake mix…turns out that was frosting. What we thought was frosting was actually custard mix. So we had to go back to the store to actually get cake mix. And the temperature the cake was baked at was for cupcakes and not a sheet pan. But in the end we figured it out and our “3 mistake cake” turned out awesome and the team was all smiles!
Signing off for now!