Monday, February 20, 2017

Pseudo-nitzschia and Those in Glass Houses

by Liz Hoke

It’s 1987 and North America smells like hairspray. The world population has passed 5 billion, a little coffee shop called Starbucks just opened up its first stores outside of Seattle, and a gallon of gas costs just shy of a dollar. It’s the same year that patients begin mysteriously flooding hospital emergency rooms on Canada’s Prince Edward Island with symptoms of vomiting, confusion, and diarrhea. The cause of this sudden influx is later found to be consumption of mussels containing high levels of a never-before seen toxin later named domoic acid12.

Domoic acid is produced by a genus of diatoms known as Pseudo-nitzschia. For humans, this poisoning causes gastrointestinal and neurological disorders that manifest within two days of consuming shellfish tainted with the life-threatening toxin. As a primary producer, Pseudo-nitzschia is a part of the foundation of the marine food-web. Transfer of domoic acid up through the trophic levels causes it to accumulate in sea animals11. Domoic acid is completely harmless to their shellfish vectors, but has been proven to be deadly to some of the people, seabirds, otters, seals, and even whales that eat them1.
Domoic acid structure

How does this work? Dominic acid wreaks neurological havoc because it acts as an analogue of glutamic acid and kainic acid, which are neurotransmitters. Neurotransmitters are essentially the chemical words that our nerve cells use to communicate with eachother. Dominic acid, however, is nearly three times as potent an excitatory molecule as kainic acid and is a full 100 times more potent than glutamic acid due to a very high binding affinity for these molecules’ receptors2. This means that if we analogize kainic acid and glutamic acid to words spoken at a conversational volume, domoic acid causes the same message to be screamed out when it really doesn’t need to be. This overstimulation leads to the degradation of nerve cells in the spinal cord13, sometimes resulting in permanent short term memory loss as well as seizures9. So what is this formidable genus that produces domoic acid?

Pseudo-nitzschia is named for the few morphological differences between it at the diatom genus Nitzschia, which is in turn named after the German zoologist Christian Ludwig Nitzsch6. As a zoology professor, Nitzch wrote about diatoms among many other things. Diatoms, with their cell walls of glass and diverse morphologies, seem more like the beads in an alien’s kaleidoscope than one of the world’s most common algae. They’re more than just a pretty face, though; these colorful drifters are responsible for 20% of the world’s photosynthetic carbon fixation5! But back to Pseudo-nitzschia, the ostensible black sheep of this glamorous family.

Circle of diatoms on a slide. Alien kaleidoscope?

Pseudo-nitzschia is a pennate (bilaterally symmetrical) diatom that often participates in annual multispecies blooms off of the West Coast of the US. Due to their nasty habit of producing domoic acid, these harmful algal blooms have been known to shut down commercial fisheries all along the coast. Thanks to the ocean’s increasing temperatures and nitrogen concentration (conditions that favor Pseudo-nitzschia growth), the East Coast has recently seen its first blooms as well14.

Should these blooms always raise high alarm for swimmers and fisheries? Not necessarily. Many studies show that these blooms produce higher levels of toxin in correlation with specific environmental factors like pH, salinity, nitrogen and iron availability, and chlorophyll a biomass7. In other words, delicate environmental conditions need to combine at specific levels to result in toxin levels high enough to be harmful to us or fishery harvests. However, because researchers still don’t have all the details of these interacting factors worked out enough to reliably predict which blooms are more harmful, caution should be exercised when blooms are present. To complicate things further, Pseudo-nitzschia is a diverse genus of over 40 recognized species, with multiple species often participating in a single bloom. One recent study worked to elucidate part of this mystery by examining Pseudo-nitzschia species diversity across vertical and horizontal environmental gradients in Puget Sound.

In this study published in 2014, researchers collected water samples from five basins in Puget Sound at various depths using a brilliant tool known to scientists as a Niskin bottle. As a Niskin bottle is lowered via cable to the desired sampling depth, a brass weight slides down the cable. The impact of the weight on the bottle causes it to tip over and trigger a spring loaded valve that seals the water sample inside. To examine the lateral distribution of phytoplankton communities, a net was towed across the surface of the water. The researchers then analyzed the Pseudo-nitzschia communities using automated ribosomal intergenic spacer analysis (ARISA), which basically means that they looked for specific DNA sequences that they already knew could be used to tell these similar species apart.  This method is useful in clarifying the Pseudo-nitzschia community structure because it not only illustrates what species are correlated with certain environmental factors, but it also shows their relative abundance in relation to each other7.
Nietzsche                                   Pseudo-Nietzsche
Created by the author
The researchers found significant correlations between species and one to eight environmental factors, as shown in the figure below.  This study is useful for scientists patching together the framework to understanding these species/environment interactions over space and time. Scientists believe this framework can illuminate which processes promote the formation of harmful algal blooms, the production of toxins, and bloom deterioration7. Developing a predictive system from this type of information is crucial to mitigating the negative effects from these algal blooms. The Woods Hole Oceanographic Institution estimates the average cost of harmful algal bloomss at nearly $450 million over a 15 year period. This estimate was developed by aggregating predicted economic impacts of harmful algal blooms on public health, commercial fisheries, recreation and tourism, and monitoring and management programs3.
Pseudo-nitzschia and environmental parameters

I don’t mean to villainize these organisms; they do a lot of good, too. Let’s not forget that the diatoms do 20% of the carbon fixation that happens on Earth. That’s not all, though. Their sensitivity to aquatic conditions makes them like glass-encased clues for forensic analysts working to diagnose death by drowning for corpses found in large bodies of water. Determining the presence of and analyzing the diatoms in decomposing bodily tissues is the most reliable method to confirm if the person aspired water, where they drowned, and to understand the aquatic conditions surrounding their death4. The cool, if not morbid, stuff isn’t negated just because these buggers can be costly when they start producing toxins.

Regardless of if you think Pseudo-nitzsche and the diatoms at large are good or bad for us, we certainly aren’t good for them. Fossils of diatoms dating back as far as 185 million years exist, so we know they’ve adapted to many climates8. However, it is also known that warmer climates decrease diatom diversity overall, which suggests that as our global temperatures continue to climb, we might be seeing less of these photosynthetic powerhouses in the future10. What does that mean for us? Maybe cheaper shrimp and oysters, but I’d prefer to keep the diatoms around. I don’t like seafood anyway.

1.     "Amnesic Shellfish Poisoning." Harmful Algae. Woods Hole Oceanographic Institute, 7 July
2016. Web. 11 Nov. 2016.

2.     "Amnesic Shellfish Poisoning (ASP)." Marine Biotoxins. Food and Agriculture Organization of
<the United Nations, n.d. Web. 11 Nov. 2016.

3.     Anderson, Donald M., Porter Hoagland, Yoshi Kaoru, and Alan W. White. Estimated Annual
Economic Impacts from Harmful Algal Blooms (HABs) in the United States. Rep. Woods Hole Oceanographic Institution. Woods Hole Sea Grant, Sept. 2000. Web. 11 Nov. 2016.

4.     Auer, Antti. "Qualitative Diatom Analysis as a Tool to Diagnose Drowning." The American
Journal of Forensic Medicine and Pathology 12.3 (1991): 213-18. MNCAT Discovery. Web. 11 Nov. 2016.

5.     Dato, Valeria Di, Francesco Musacchia, Giuseppe Petrosino, Shrikant Patil, Marina
Montresor, Remo Sanges, and Maria Immacolata Ferrante. "Transcriptome Sequencing of Three Pseudo-nitzschia Species Reveals Comparable Gene Sets and the Presence of Nitric Oxide Synthase Genes in Diatoms." Scientific Reports 5 (2015): n. pag. MNCAT Discovery. Web. 11 Nov. 2016. 

6.     Hasle, Grethe Rytter. "Pseudo-Nitzschia As A Genus Distinct From Nitzschia
(Bacillariophyceae)." Journal of Phycology 30.6 (1994): 1036-039. MNCAT Discovery. Web. 11 Nov. 2016.

7.     Hubbard, Ka, Ce Olson, and Ev Armbrust. "Molecular Characterization of Pseudo-nitzschia
Community Structure and Species Ecology in a Hydrographically Complex Estuarine System (Puget Sound, Washington, USA)." Marine Ecology Progress Series 507.39-55 (2014): 39-55. Web. 11 Nov. 2016.

8.     Kooistra, Wiebe H.c.f., and Linda K. Medlin. "Evolution of the Diatoms (Bacillariophyta)."
Molecular Phylogenetics and Evolution 6.3 (1996): 391-407. MNCAT Discovery. Web. 11 Nov. 2016.

9.     Lasoff, Daniel, MD, and Binh Ly, MD. "Amnesic Shellfish Poisoning." Call Us... 14 (19 Feb.
2016): n. pag. California Poison Control System. Web.

10.  Lazarus, David, John Barron, Johan Renaudie, Patrick Diver, and Andreas Türke. "Cenozoic
Planktonic Marine Diatom Diversity and Correlation to Climate Change." PLoS ONE 9.1 (2014): n. pag. MNCAT Discovery. Web. 11 Nov. 2016.

11.  Lopes, Vanessa, Ana Lopes, Pedro Costa, and Rui Rosa. "Cephalopods as Vectors of Harmful
Algal Bloom Toxins in Marine Food Webs." Marine Drugs 11.9 (2013): 3381-409. MNCAT Discovery. Web. 11 Nov. 2016.

12.  Ragaini, Richard C. Society and Structures: Proceedings of the International Seminar in
Nuclear War and Planetary Emergencies, 29th Session, Erice, Italy, 10-15 May 2003. Singapore: World Scientific, 2003. Print.

13.   "Red Tide." Harmful Algae. Woods Hole Oceanographic Institute, 31 July 2012. Web. 11
Nov. 2016.

14.  "West Coast Harmful Algal Bloom." National Ocean Service News. National Oceanic and
Atmospheric Administration, 2 May 2016. Web. 11 Nov. 2016.