Molecular mechanism of oil induced growth inhibition in diatoms

Manoj Kamalanathan, Savannah Mapes, Jessica Hillhouse, Noah Claflin, Joshua Leleux, David Hala, Antonietta Quigg

Abstract: The 2010 Deepwater Horizon oil-spill exposed the microbes of Gulf of Mexico to unprecedented amount of oil. Conclusive evidence of the underlying molecular mechanism(s) on the negative effects of oil exposure on certain phytoplankton species such as Thalassiosira pseudonana is still lacking, curtailing our understanding of how oil spills alter community composition. We performed experiments on model diatom T. pseudonana to understand the mechanisms underpinning observed reduced growth and photosynthesis rates during oil exposure. Results show severe impairment to processes upstream of photosynthesis, such as light absorption, with proteins associated with the light harvesting complex damaged while the pigments were unaffected. Proteins associated with photosynthetic electron transport were also damaged, severely affecting photosynthetic apparatus and depriving cells of energy and carbon for growth. Negative growth effects were alleviated when an organic carbon source was provided. Further investigation through proteomics combined with pathway enrichment analysis confirmed the above findings, while highlighting other negatively affected processes such as those associated with ferroxidase complex, high-affinity iron-permease complex, and multiple transmembrane transport. We also show that oxidative stress is not the primary route of negative effects, rather secondary. Overall, this study provides a mechanistic understanding of the cellular damage that occurs during oil exposure to T. pseudonana.

Negatively affected biological functions or gene ontology terms in T. pseudonana after 48 h of exposure to WAF relative to Control. The size of the node corresponds to the size of the gene sets and the color of the node ranging from orange-white-blue indicates increasing FDR q values.

Role of polysaccharides in diatom and its associated bacteria in hydrocarbon presence

Manoj Kamalanathan, Meng-Hsuen Chiu, Hernando Bacosa, Kathy Schwehr, Shih-Ming Tsai, Shawn Doyle, Alexandra Yard, Savannah Mapes, Carlos Vasequez, Laura Bretherton, Jason B. Sylvan, Peter Santschi, Wei-Chun Chin, Antonietta Quigg

Abstract:

Diatoms secrete a significant amount of polysaccharides, which can serve as a critical organic carbon source for bacteria. The 2010 Deepwater Horizon oil spill exposed the Gulf of Mexico to substantial amounts of oil that also impacted the phytoplankton community. Increased production of exopolymeric substances was observed after this oil spill. Polysaccharides make up a major fraction of exopolymeric substances; however, their physiological role during an oil spill remains poorly understood. Here, we analyzed the role of polysaccharides in the growth and physiology of the oil-sensitive diatom Thalassiosira pseudonana and how they shape the surrounding bacterial community and its activity in the presence of oil. We found that inhibition of chrysolaminarin synthesis had a negative effect on the growth of T. pseudonana and intracellular monosaccharide accumulation, which in turn suppressed photosynthesis by feedback inhibition. In addition, by acting as a carbon reserve, chrysolaminarin helped in the recovery of T. pseudonana in the presence of oil. Inhibition of chrysolaminarin synthesis also influenced the bacterial community in the free-living fraction but not in the phycosphere. Exposure to oil alone led to increased abundance of oil-degrading bacterial genera and the activity of exoenzyme lipase. Our data show that chrysolaminarin synthesis plays an important role in the growth and survival of T. pseudonana in the presence of oil, and its inhibition can influence the composition and activity of the surrounding bacterial community.

Electron microscope images of T. pseudonana cultures under the different experimental conditions. A–D, Representative SEM images (out of nine images per treatment) of T. pseudonana grown under Control (A), WAF (B), Control+DCB (C), and WAF+DCB (D) conditions taken on d 3 of the experiment. Scale bars = 2 µm.

Turning the (red) tide on forecasts?

Mote shelf survey aimed at improving predictions of the noxious algal blooms

Article By:

Elizabeth Djinis

elizabeth.djinis@heraldtribune.com

Link: https://www.jacksonville.com/story/news/local/sarasota/2017/07/08/motes-shelf-survey-could-help-scientists-improve-red-tide-forecasts/20282915007/

David Gordon, a staff scientist in the chemical and physical ecology department at Mote, watches as phytoplankton ecology intern Savannah Mapes marks samples. [Herald-Tribune staff photo / Elizabeth Djinis] Sarasota Herald-Tribune

GULF OF MEXICO — While the circular rosette balancing six hydraulic tubes lightly breaks the surface of the water, scientists aboard the nearby boat scramble to hoist the machinery on deck.

Soon, they will open the tubes and pour each of the samples, taken at three different water depths, into a labeled container. As the rosette travels through the water, it collects data on temperature, salinity, water cloudiness and other factors that could play a role in the nutrients and organisms present.

The samples will then return to the lab, where scientists will filter and analyze them for particular elements, such as Karenia brevis, the toxic Florida red tide organism. The expedition is part of Mote Marine Laboratory's shelf survey, a research project conducted every eight weeks at 14 stations within the West Florida Shelf, where scientists believe the red tide bloom originates.

Red tide is infamous for its effect on Florida beaches, marked by a bad smell, dead fish that wash up on shore and serious respiratory irritation in people. The harmful algae's toxin can kill birds and other animals, including the iconic manatee; an estimated 300 manatees were killed by red tide in 2013.

Consuming shellfish with red tide toxins can lead to a health condition called neurotoxic shellfish poisoning, which can cause neurological and gastrointestinal symptoms.

The environmental phenomenon also has a significant economic impact on health and tourism. In 2000, a Florida Fish and Wildlife Conservation Commission study found that attendance of Sarasota County public beaches fell by almost 50,000 visitors in months with red tide. A federal study, cited by U.S. Rep. Vern Buchanan, R-Longboat Key, in a push for more research funding, estimated that the nation's seafood, restaurant and tourism industries sustain $82 million in economic losses restaurant and tourism industries each year due to red tide and other harmful algal blooms.

So although some of the scientists on board jokingly call the sampling process "catching water," they hope that the ongoing data collection will one day take on a higher significance. One of their goals is to predict and forecast when a red tide bloom might occur. And that means taking water samples when red tide is absent, says Vincent Lovko, the program manager for Mote's phytoplankton ecology department.

"Even when there's not a red tide, we still need to go out there and sample," Lovko said. "The whole intention is to develop the capability of forecasting and predicting red tide, and we can't do that without the information from when there's not a red tide."

When Lovko talks about red tide, he often compares it to the weather. Whereas meteorologists can predict whether a thunderstorm or rain showers are expected in the next few days, scientists are not yet at that level with red tide. Forecasting models exist, evidenced by efforts such as the National Oceanic and Atmospheric Administration's red tide forecasts and the University of South Florida's College of Marine Science's Collaboration for Prediction of Red Tides project along with the Florida Fish and Wildlife Conservation Commission. But these predictions are not without significant error, Lovko added.

"Last year, (USF's) model had said there wasn't going to be a significant bloom," he said.

In contrast, the past year saw one of the most persistent blooms in recent history, continuing on and off from last fall until late April.

"So their model needs some work," he said.

Making predictions

One of the major flaws with most forecasting systems is the difficulty of combining physics, biology and nutrients to make a prediction, said Kate Hubbard, a research scientist with the Florida Fish and Wildlife Research Institute.

Most forecasting models take physics into account, including ocean circulation, but do not always consider other factors that may have an impact. Eventually, Hubbard said these 3.5-day forecasts could turn into seasonal forecasts.

"What we're trying to do is look at these processes over a very short-term time schedule and then also long-term time scale," Hubbard said. "We're trying to constrain a lot of those different parameters and do that in such a way that we can make those sorts of predictions and extend realistically."

Through collecting data at various depths and times of year, Lovko hopes that the water samples will shed light on patterns that occur prior to a red tide bloom, during a bloom and once a bloom has gone.

Once they understand those, scientists have a better shot at being able to more accurately predict when and where red tide may occur.

"What's happening in the water column on the shelf gives us clues as to whether or not we're going to have a bloom and to make those connections between what conditions precede a bloom," Lovko said.

At the end of its second year, the survey program has funding for at least five years total, according to Lovko. While water samples of the Florida red tide organism exist from as far back as the 1950's, it wasn't until 2000 that scientists began regularly taking samples when a bloom was not in existence, Lovko added. That makes it difficult to identify forecasting trends in such a small data set.

But forecasting is not the most popular question residents ask Lovko about red tide, perhaps the state's least favorite tourist. Instead, they wonder: what are scientists doing to get rid of red tide?

Again, Lovko brings up the weather.

"We don't try to change the weather; we try to get better at predicting it," he said. "But as scientists, it's within our obligation to find out what's possible."

Following that logic, Lovko's team is quietly working on an experiment using a parasite that specifically targets dinoflagellates, a type of plankton which includes the red tide organism. How that could help control red tide -- and whether scientists would even want to -- remains to be seen. Lovko is not yet ready to discuss the experiment further.

People "think that our goal is to just get rid of it," Lovko said. "But we have to ask: is that even feasible and is that advisable?"