Keith Bouma-Gregson’s exit talk

What you must know before reading this blog is that here at Berkeley most talks are great. You could go to a seminar every single day and learn new things and hear brilliant people talking. This also applies to graduate students‘ exit talks. The last one I went to was by Tristan Nunez. See here.

Today it is Keith Bouma-Gregson. He did a PhD in Mary Power’s lab in Integrative Biology at UC Berkeley. He will be moving on to work with Jill Banfield now. Check her out. She is awesome.

Mary Power’s introduction:

Keith worked on a variety of projects on food web ecology, aquatic ecology, cyanobacterial genomics (mostly Phormidium: a toxic cyanobacterium), public health and citizen science. He also worked a lot on the Eel river restoration project. Keith involved local people so that they would learn what the problems are with cyanobacteria and the toxins that they produce.

There is a funny, dark, little story. Somebody found a human skull in a river in Humboldt County. The police wanted to use their sniffing dogs to find the rest of the body but they did not know whether they could let their dogs into the water because of the toxic cyanobacteria. So Keith went there and checked it for them. He could confirm that the waters were safe. So whenever these detectives will have similar problems they know now who they have to contact…

Full hearts, clear eyes on the eel can’t lose. FULL HEARTS, CLEAR EYES ON THE EEL CAN’T LOSE. (you have to scream it out loud).

OK. Now Keith will start his talk:

Background: Water systems in California have been affected heavily by human alterations like pollution, damming, or the addition of fertilizers. The climate in California is mediterranean, the highest water levels occur at the wrong time for agriculture. Hence, humans built dams and reservoirs for saving it. Consequently, there is not enough water for the ecosystem when it needs it for its highest productivity. Due to the huge anthropogenic impacts on Californian waters, cyanobacterial blooms have increased. These bacteria will bloom and become the most common taxa in the environment. Legrand et al. showed in the journal Toxins in 2017 that cyanobacterial blooms are increasing recently (shown in Lake Zurich, Switzerland). Cyanobacteria produce toxins that are harmful to the mammalian liver and nerves. Not all strains contain the genes to produce these toxins.

Keith’s thesis: was based on the Eel River system. UC Berkeley has a field station in the middle of this system, the Angelo Coast Range Reserve. By the way, I did a large part of my fieldwork on O. mykiss in this reserve. Keith monitored the Eel River for cyanobacteria. He wanted to find out where, when and who is there. Together with Professor Kudela at UC Santa Cruz, Keith built Solid Phase Absporption Toxin Trackers (SPATTs) to measure toxins in the water. The toxin Anatoxin-a showed very high levels throughout the watershed. The highest levels were measured in August when the river temperatures were highest. At this point, Keith did not know which taxa were producing these toxins.

Keith went ahead and identified all cyanobacteria he could find in the system. He described mostly Anabaena spp. (Nostocales) and Phormidium spp. (Oscillatoriales). To do this, Keith collected green mats in the field, brought them to the lab and measured their toxin concentrations. He could find Anatoxin-a and Microcystin toxins in all mats. The levels were so high that they would kill a dog and maybe even be toxic to a cow. Moreover, Anabaena spp. were associated with low flowing water. It builds clumps and they get stuck in eddies and pools of the river. This could be a health risk for humans swimming in the river. Keith performed an experiment to investigate when cyanobacteria float and when they sink to the ground in the natural river. He found that they remain buoyant for days in a natural light regime (Bouma-Gregson et al. in Harmful Algae 2017).

He learned the following:

  • Cyanotoxins are produced by benthic Anabaena and Phormidium.
  • Anatoxin-a is frequent and shows high concentrations.
  • Cyanobacteria float at high concentrations in the river during summer and could represent a potential health risk.

As a next step, Keith performed genome resolved metagenomics. He collected cyanobacteria at 22 different sites across the Eel River system, extracted their DNA and assembled them into contigs to get a draft metagenome. Then he binned out individual genomes into draft genomes. With these samples he would first describe the bacterial composition and then look for the Anatoxin-a synthesis operon. He could find this operon in 7 samples. Then he linked the presence/absence of this operon to bacterial community composition. He found that samples with this operon clustered together. This was mostly driven by the presence of Burkholderiales.

Keith also identified the main energy pathways in his microbial mats. Most bacteria in his samples had genes for carbon oxidation. He did not find any bacteria that use methane, hydrogen or sulfate to gain energy. However, he found a few bacteria that metabolize Urease. Many of his bacteria contained a gene that codes for a transporter that can transport phosphate inside their bodies. Moreover, they also have a pathway where they excrete an enzyme into their environment that binds inorganic phosphorus and transforms it to phosphate which they then can import back into their cells. It seems that these bacteria are super effective at scavenging phosphorus, even if its concentrations are low. This could be an explanation why Phormidium dominates in the Eel river system that has high organic nitrogen levels and low phosphorus levels.

Keith ended his talk with the following statement: Cyanobacteria have been around in our environment ‚forever‘ so the goal should not be to eradicate them but to learn more about them and how to deal with them.

This is Keith. He is also active on twitter as @K_BoumaGregson



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