Thursday, December 29, 2016

More than meets the eye: the development of a complex eye structure in Warnowiids

by JT

In the world of microbiology, it’s always the most outrageous microbes that get all the buzz. Prokaryotic microbes, like Escherichia coli are usually the first examples of microbiology that come to most people’s mind. When you think about eukaryotic microbiology, yeasts like Saccaromyces cerevisiae involved in brewing and baking are the model examples. Or some insane fungi that can grow in and out of a host – I’m looking at you, Cordyceps.

Then there are the microbes that just do some weird, but awesome stuff by themselves. Like the warnowiids.


The warnowiids are a little bit like the cousin you hear about at family reunions – they’re always doing something cool, but you’re not quite sure how they’re doing it, and you never really see them either. So what makes warnowiids so cool? They’re unicellular eukaryotic microbes that are flagellate protists, and have developed a complex eye structure called the ocelloid.

The ocelloid isn’t like a simple eyespot that has photoreceptors and allows the cell to respond to light. Instead, the ocelloid is made of similar structures that are analogous to what you might see in a human eye, although the exact function of the ocelloid is unknown (Figure 1). The ocelloid has a lens called the hyalosome, a cornea, an iris-like region, and a segment full of pigments called the retinal body (1). The retinal body functions similarly to how the retina works in our eyes, and is thought to function as a light sensitive component of the structure (Figure 2).

Figure 1. Microscopy and Illustrations of theOcelloid. Light micrograph (left), illustration (middle), and electron micrograph (right) of the ocelloid. The parts of the ocelloid and their evolutionary origins are labeled on the illustration.   

Figure 2: Analogous structures of the ocelloid andhuman eye. The ocelloid (left) has structures that are similar in function to structures in the human eye (right). H is the hyalosome, C is the crystalline lens, and R in both illustrations is the retina or retinal body.   
So you’ve got a unicellular organism capable of developing a highly complex structure typically reserved for multicellular organisms, and not just any multicellular organisms. The ocelloid structure was observed to be similar to multicellular camera-type eyes that evolved independently in different cephalopods and vertebrates (2).

These discoveries bring up some important food for thought. What role does multicellularity really play in the development of specialized structures such as the eye, if a single celled microbe can develop an analogous structure in the ocelloid? How did this development even happen? Why favor a complex ocelloid over a simpler eyespot? What are the evolutionary forces that drove the warnowiids to adapt this structure?

However, answering these questions wasn’t so easy due to how warnowiids grow and where they grow. Warnowiids are unable to be cultivated in a lab, making it difficult to grow and keep these cells viable for experiments. So why not just find isolates in the environment and just use those instead? The other problem is that warnowiids are also rare in the wild. They are typically found on plankton in marine environments, but they are found with rates of only one or two cells isolated from plankton per year (1). One or two cells! You’d have better luck finding affordable college education at that rate. Despite these obstacles, a few studies have come out in the last ten years detailing the structure and function of the ocelloid, as well as its evolutionary history.

In one study, researchers used electron microscopy and tomography to investigate the structure of the ocelloid (1). Electron microscopy uses electrons and tomography uses an ion beam to obtain images of the ocelloid. The authors also used genomics, both isolated organelle and single cell genomics in order to study the makeup of the ocelloid. What built the structures of the ocelloid?

It turns out that the ocelloid might be derived from different organelles. Previously, the retinal body was reported to have thylakoid-like structures. Typically, thylakoids are found within chloroplasts, and usually are the site of the light dependent reactions of photosynthesis. By using electron microscopy, the researchers found that during cell development, the retinal body appeared to be derived from a plastid-like structure with double stacked thylakoids (1). Plastids are organelles that usually house pigments used in photosynthesis, so this discovery brings into question what the function of the retinal body is if it contains these light harvesting proteins.

The researchers also used electron microscopy to examine the lens of the ocelloid, the hyalosome. They found that the lens contained a sheet of individual mitochondria that were connected to the cytoplasmic mitochrondria nearby. With the discovery of both thylakoid-like structures and mitochondria present in the ocelloid, the authors concluded that the ocelloid was composed of different organelle components. Mitochondria, similar to plastids, are thought to have an endosymbiotic relationship with warnowiids.

The researchers suggested that the presence of these plastid-like structures with thylakoids might indicate the ancestor of warnowiids were photosynthetic, helping to possibly narrow down what the evolutionary path of warnowiids might have been. There is also the question of where these plastids were derived from in the first place. In dinoflagellates, which warnowiids are a part of, plastids are thought to originate from endosymbiosis with red algae (1). Coupled with the mitochondria sheets found in the lens, these conclusions suggest that the ocelloid incorporates different endosymbiotic organelles together in order to form this complex structure.

Whoa. So instead of undergoing cell differentiation or similar mechanisms by which our own multicellular eyes develop, the warnowiids instead create a hodgepodge of different organelles in the form of mitochondria and plastids to achieve complexity. In some ways, the warnowiids have adopted a “fake it ‘till you make it” mentality when it comes to producing a complex structure of their own analogous to a multicellular structure found in our eyes.

So we’ve elucidated what we think the structure looks like, what its composed of, but what does it actually do? In another study, the researchers sought to determine the function of the ocelloid by determining if the structure was photoreceptive (3). The researchers examined the ocelloid using electron microscopy in two different light conditions, in a light adapted state and a dark adapted state (3). They found that the retinal body in the light adapted state had thicker lamellae compared to the dark adapted state. That is, the total surface area of the retinal body became larger in the dark adapted state, suggesting that the ocelloid does play a role in responding to light and dark conditions as a larger surface area has more chance to gather light. The researchers also found that the hyalosome can also play a role in light sensitivity by concentrating dim light (3). With these conclusions, the researchers determined that the ocelloid does play a role in sensing light and functions as an ocular structure.

As we figure out methods to cultivate organisms that were previously only able to be isolated from the wild, more experiments can be done on warnowiids to further investigate the evolutionary path that these organisms took in order to develop the ocelloid structure. This is important in two ways. One, the fact that ocelloids developed not out of multicellularity, but instead, a chimeric combination of different organelles provides another way to how complexity can be achieved in organisms. Second, the evolutionary forces that drove warnowiids to develop ocelloids might serve as an example of driving forces for other evolutionarily mysterious structures found in different organisms.

Warnowiids might not be in the public eye (no pun intended) as much as yeast, or fungi, or even other protists, but their unique development of a complex structure without multicellularity provide insights on how evolution could have driven this process, as well as how different photoreceptive structures in organisms are made and what their function is. Due to the difficulties in obtaining warnowiids, not many experiments have been done on these unique organisms, but in the next couple of years, we might be seeing more of these guys as cultivation techniques improve.

Keep an eye on them.  


1.         Gavelis GS, Hayakawa S, White Iii RA, Gojobori T, Suttle CA, Keeling PJ, Leander BS. 2015. Eye-like ocelloids are built from different endosymbiotically acquired components. Nature 523:204–207.
2.         Hoppenrath M, Bachvaroff TR, Handy SM, Delwiche CF, Leander BS. 2009. Molecular phylogeny of ocelloid-bearing dinoflagellates (Warnowiaceae) as inferred from SSU and LSU rDNA sequences. BMC Evol Biol 9:116.
3.         Hayakawa S, Takaku Y, Hwang JS, Horiguchi T, Suga H, Gehring W, Ikeo K, Gojobori T. 2015. Function and evolutionary origin of unicellular camera-type eye structure. PloS One 10:e0118415. 

4 Things You Didn’t Know About an Ectomycorrhizal Fungi. Number 3 Will Shock You (or Not)!

by AT

When talking about fungi, many people first think about mushrooms like the brown Portabellas that we use in cooking (which are actually just a matured version of the white mushrooms). But wait, there’s more! Besides mushrooms, there are other types of fungi. For example, there are fungi that actually form a symbiotic relationship with plants! Like a cat and its owner, symbiosis involves two different species doing good things for each other despite not needing each other. Some of these symbiotic fungi associate with plant roots and are called ectomycorrhizal fungi. In these relationships, the ectomycorrhizal fungi scavenge for nutrients and share these nutrients with their hosts in exchange for carbon fixed by plant photosynthesis.6 With that, here are five things you didn’t know (to be honest, you probably didn’t know it even existed) about an ectomycorrhizal fungi called Cenococcum geophilum (C. geophilum).

Fig 1. See that black stuff? That’s Cenococcum geophilum on
root tip. The white scale bar is 200 micrometers long.1

1. C. geophilum had several other names before. Talk about an identity crisis…
       Although C. geophilum is the official name for the species, it has historically been called other names such as Lycoperdon graniforme and Cenococcum graniforme.3 It was first named Lycoperdon graniforme by James Sowerby in 1800. In 1825, Elias Fries introduced the genus name of Cenococcum, replacing Lycoperdon. Several years later, the name C. geophilum was introduced, however, it was still interchangeable with Cenococcum graniforme for many years before C. geophilum was established as the official name. Finally.

2. Got trees? C. geophilum can form symbiotic relationships with many different hosts in different places.
            C. geophilum can pretty much grow anywhere. Other common ectomycorrhizal usually associate with just one plant host, but C. geophilum is known to associate with any plant that is capable of hosting ectomycorrhizal fungi. However, it is most commonly found in temperate forests.7 You can generally find C. geophilum growing on the roots of various pine, oak, birch, willow, and aspen trees all over Europe and North America. Also, it is commonly found as far north as the tundra of northern Alaska and as far south as Florida.7 Wet or dry soils, this fungus can take it all. Under conditions that aren’t looking too good, C. geophilum can form sclerotia, which are large masses of hardened mycelium that are resistant to harsh environmental conditions.3 In C. geophilum, the sclerotia are known to survive for several years. When there are more sunshine and rainbows, the sclerotia germinate to reestablish fungal communities. With such an ability to grow in different regions, it would be no surprise to find this fungus in other areas around the world like the tropics. In fact, it’s been found in Puerto Rico!7 Look no further for the fungal jack-of-all-trades.

3. C. geophilum could be very important to establishing forests. Stunning, tree-mendous, forests.
            Because C. geophilum is a very common ectomycorrhizal fungus, it has also been well studied since its discovery in 1800. An interesting recent discovery was how the production of melanin, a complex dark polymer, in the cell walls of hyphae helps the fungus resist dry conditions.2 If an ectomycorrhizal fungus is resistant to drought conditions, then this resistance probably benefits the survival of the host tree as well. As an example, if the ectomycorrhizal fungus dies during a drought, the tree can survive, but it essentially becomes widowed. Then, the poor tree will need to establish a new relationship with an ectomycorrhizal fungus to obtain the nutrients provided by the previous symbiotic relationship. Otherwise, the tree can’t get enough water, and it could die too. Even if it found a new symbiotic partner, the partner may not provide the same nutrients in equal amounts. When forests are just getting established, this change could have bigger impacts because young trees cannot process as much water compared to older trees. Having drought-resistant fungi in the first place is probably better for both the plant and the fungus, because the plant will not have to find a new friend, and the fungus doesn’t have to die. So as soon as California gets some rain, planting some trees with C. geophilum might help the trees tolerate drought better.

4. C. geophilum responds to different levels of Nitrogen, sometimes not very well.
            Like many other soil fungi, C. geophilum cannot fix free nitrogen from the air. It is able grow using ammonium (NH4+), nitrate (NO3-), and amino acids as its nitrogen source, but it likes to utilize ammonium the most.7 But like work, too much available nitrogen can have a detrimental effect on the abundance of this fungus. In a 2008 study, researchers found that as nitrogen availability increases, C. geophilum becomes less common on the roots of red spruce trees.5 This decrease is not small; it drops from being present in 90% of the roots to about 50% when the nitrogen concentration in roots doubles. In the last century, human activity has doubled the amount of nitrogen deposited into the ground, which is expected to continue increasing.8 Things like fertilizers and manure really increase the amount of nitrogen in soils, and farming uses a whole lot of it. With this ever-increasing amount of nitrogen in the world’s soil, it is possible that C. geophilum will become less important in plant symbiosis. This is because the plant now has an easier time getting nitrogen without the help of C. geophilum. It’s like going to your friends’ house all the time to see their puppies, but then your significant other buys one for you instead. However, other fungi aren’t at a loss. When the nitrogen availability increases, the frequency of some other ectomycorrhizal fungi increases, but these other fungi are not as common as C. geophilum.5 For our Midwestern friends, think about how the ectomycorrhizal fungi in your front-yard tree will be affected when you decide to sprinkle that grass fertilizer onto your lawn. You may get end up with a beautiful yard, but C. geophilum is hurting from losing its friend.
            On a general level, nitrogen can also affect an ectomycorrhizal community. Another study found that the concentration of nitrogen in the soil also affects how fast different ectomycorrhizal fungi decompose when they die.4 For C. geophilum, the biomass decays about 35% in one month, which was less decomposition than the other ectomycorrhizal fungi that were tested. These other fungi also had a higher concentration of nitrogen in their tissues, possibly meaning that a higher tissue concentration of nitrogen resulted in a higher decomposition rate. However, an increased nitrogen availability didn’t really change the decomposition rate of C. geophilum. In fact, it actually decayed less than several other types of ectomycorrhizal fungi in the same amount of time. So even though C. geophilum gets left out of the symbiotic relationship when nitrogen levels increase, it sticks around when it dies, almost as if it wants to guilt the tree for leaving it behind.

There you have it: 5 things you didn’t know about C. geophilum! Do you think have learned a ton of new things? Take the quiz and find out how much you now love and understand C. geophilum! (Actually, there is no quiz.)


1. Cenococcum geophilum [homepage on the Internet]. Wikipedia. 2016 Nov 15 [cited 2016 Dec 5]. Available from:

2. Fernandez CW, Koide RT. The function of melanin in the ectomycorrhizal fungus cenococcum geophilum under water stress. Fungal Ecology. 2013; 6(6): 479-486.

3. Fernández-Toirán L, Águeda B. Fruitbodies of cenococcum geophilum. Mycotaxon. 2007; 100: 109-114.

4. Koide RT, Malcolm GM. N concentration controls decomposition rates of different strains of ectomycorrhizal fungi. Fungal Ecology. 2009; 2(4): 197-202.

5. Lilleskov EA, Wargo PM, Vogt KA, Vogt DJ. Mycorrhizal fungal community relationship to root nitrogen concentration over a regional atmospheric nitrogen deposition gradient in the northeastern USA. Canadian Journal of Forest Research. 2008; 38(5): 1260-1266.

6. Talbot J, Allison S, Treseder K. Decomposers in disguise: Mycorrhizal fungi as regulators of soil C dynamics in ecosystems under global change. Funct Ecol. 2008; 22(6): 955-963.

7. Trappe JM. Cenococcum graniforme--its distribution, ecology, mycorrhiza formation, and inherent variation. 1962.

8. Zak DR, Pregitzer KS, Burton AJ, Edwards IP, Kellner H. Microbial responses to a changing environment: Implications for the future functioning of terrestrial ecosystems. Fungal Ecology. 2011; 4(6): 386-395.