by Cliff Bueno de Mesquita
In our recent and ongoing experiments on the effects of herbicides on soil microbes, we found one species of fungus, Mortierella elongata, that was not negatively affected by the herbicide Glyphosate (ingredient in Roundup), and actually responded positively to the surfactant it is usually spread with, Agridex. Soils collected from the nearby Chatfield Farm outside of Denver had received treatments of Glyphosate, Agridex, Promax (another surfactant), Agridex and Glyphosate combined, and controls with no chemical additions.
M. elongata is a fungus in the Mucoromycota phylum. Mortierella species are typically saprotrophs but also grow on the surface of roots. They are capable of degrading complex carbon compounds such as chitin and hemicellulose. They reproduce via formation of thick-walled spores called zygospores, which are produced by many other species of fungi as well as algae (Gams, Chien, and Domsch 2009). Typically, they are not pathogenic.
Figure 1. Morphology of Mortierella elongata CNUFC-YR329-1. A, D colony on potato dextrose agar; B, E colony on oatmeal agar; C, F colony on water agar; (A-C: observed view, D-F: reverse view). G-I young sporangia on sporangiophores; J the collar at the top of the sporangiophore (white arrow). K sporangiosphores (scale bars: G-K ¼ 20 lm). From Nguyen et al. 2019.
M. elongata has been isolated and cultured. It produces Arachidonic acid (an omega-6 fatty acid also found in red meat), as well as Eicosapentaenoic acid (also known as EPA omega-3 fatty acid), both of which people take as supplements (Bajpai, Bajpai, and Ward 1991; Yamada, Shimizu, and Shinmen 1987). However, it appears that there was never large-scale commercial production of M. elongata for those purposes. Another interesting thing about this fungus is it contains a bacterium inside of it, called an endobacterium, which was identified as Mycoavidus cysteinexigens (Ohshima et al. 2016). Researchers suggested that this endobacterium was responsible for the production of nitrous oxide (Sato et al. 2010), a greenhouse gas, and there has been considerable interest in the bacterium, as its whole genome has been sequenced and assembled (Fujimura et al. 2014).
Our result with M. elongata highlights the importance of studying chemicals used to help spread herbicides, in addition to the herbicide itself. Stay tuned in future months for more results from our herbicide experiment!
Bajpai, P., P. K. Bajpai, and O. P. Ward. 1991. “Eicosapentaenoic Acid (EPA) Formation: Comparative Studies with Mortierella Strains and Production by Mortierella Elongata.” Mycological Research 95(11): 1294–98. http://dx.doi.org/10.1016/S0953-7562(09)80577-7.
Fujimura, R. et al. 2014. “Draft Genome Sequence of the Betaproteobacterial Endosymbiont Associated with the Fungus Mortierella Elongata FMR23-6.” Genome Announcements 2(6): 2010–11.
Gams, W., Chiu-Yuan Chien, and K.H. Domsch. 2009. “Zygospore Formation by the Heterothallic Mortierella Elongata and a Related Homothallic Species, M. Epigama Sp.Nov.” Transactions of the British Mycological Society 58(1): 5–13. http://dx.doi.org/10.1016/S0007-1536(72)80065-2.
Nguyễn, Thưởng & Won Park, Se & Pangging, Monmi & Lee, Hyang. (2019). Molecular and Morphological Confirmation of Three Undescribed Species of Mortierella from Korea. Mycobiology. 47. 31-39. 10.1080/12298093.2018.1551854.
Ohshima, Shoko et al. 2016. “Mycoavidus Cysteinexigens Gen. Nov., Sp. Nov., an Endohyphal Bacterium Isolated from a Soil Isolate of the Fungus Mortierella Elongata.” International Journal of Systematic and Evolutionary Microbiology 66(5): 2052–57.
Sato, Yoshinori et al. 2010. “Detection of Betaproteobacteria inside the Mycelium of the Fungus Mortierella Elongata.” Microbes and Environments 25(4): 321–24. http://joi.jlc.jst.go.jp/JST.JSTAGE/jsme2/ME10134?from=CrossRef.
Yamada, Hideaki, Sakayu Shimizu, and Yoshifumi Shinmen. 1987. “Production of Arachidonic Acid by Mortierella 1S-5.” Agricultural and Biological Chemistry 51(3): 5–10.
by Adam Solon
When studying eukaryotic microbes, familiar groupings such as fungi, green algae, and micro animals, such as Tardigrades (water bears!), are usually found in communities. However, there also exists a large diversity of life that do not fit into those taxonomic assignments. Many are members of the broad grouping known as Protists. Protists are not united in any sort of phylogenetic connection and exist as a catchall for eukaryotic microbes that are not fungi, green algae, or animals. Among those are the organisms that make up the SAR supergroup (Stramenopiles, Alveolates, and Rhizaria). The Stramenopiles include a wide range of organisms including kelp, diatoms, and parasites such as the genus Phytophthora, infamous for causing the Great Irish Potato famine (Derelle et al. 2016). When conducting a lab experiment with soils from Antarctica we found large relative abundances of Xanthophyceae, a member of the Stramenopiles group.
Xanthophyceae are a taxonomic class of the Stramenopiles and have the common name yellow-green algae. While they have the name algae, they are distantly related to the more commonly known green algae. Morphological-physiological characteristics that distinguish Xanthophyceae include: photosynthesis (i.e. use sunlight for energy, like plants), heterokonate (i.e. two flagella (threadlike appendages typically used for swimming) of different lengths, one forward tinsel flagellum and one backward whiplash flagellum); and capability of asexual or sexual reproduction (Sahoo & Kumar 2015). They also have a wide variety of characteristics in which they may differ including: uninucleate or multinucleate; unicellular, colonial or filamentous; and various combinations of the following pigments which give them a yellowish-green color- chlorophyll a and c, β-carotene and xanthophylls (Maistro et al. 2017). One of the clear distinctions between yellow-green algae and green algae is a lack of chlorophyll b in yellow-green algae.
Typically found in freshwater and moist soils, with a few in marine habitats, Xanthophyceae have been discovered in both polar regions (Novis et al. 2015, Kvíderová & Elster 2017). Using soils collected from Taylor Valley in the Dry Valleys of Antarctica, we introduced inputs of water along with an initial treatment of nitrogen and phosphorus to the normally dry, oligotrophic (nutrient poor) soils from this polar desert. These little critters were able to take advantage of those nutrient additions and the subsequent water inputs and contributed to the development of a biocrust that formed on the surface. Our DNA-seq analysis revealed they made up a significant level of relative abundance in those crusts (Fig 1).
Derelle, R., López-García, P., Timpano, H., & Moreira, D. (2016). A phylogenomic framework to study the diversity and evolution of stramenopiles (= heterokonts). Molecular biology and evolution, 33(11), 2890-2898.
Kvíderová, J., & Elster, J. (2017). Photosynthetic activity of Arctic Vaucheria (Xanthophyceae) measured in microcosmos. Czech Polar Reports, 7(1), 52-61.
Maistro, S., Broady, P., Andreoli, C., & Negrisolo, E. (2017). Xanthophyceae. Handbook of the Protists, 407-434.
Novis, P. M., Aislabie, J., Turner, S., & McLeod, M. (2015). Chlorophyta, Xanthophyceae and Cyanobacteria in Wright Valley, Antarctica. Antarctic Science, 27(5), 439-454.
Sahoo, D., & Kumar, S. (2015). Xanthophyceae, Euglenophyceae and Dinophyceae. In The algae world (pp. 259-305). Springer, Dordrecht.
by Cliff Bueno de Mesquita
This month I’ll write about another microbe from my litter addition experiment. One of the dominant fungi on/in the leaves of the alpine cushion plant Silene acaulis was Phaeosphaeria silenes-acaulis, which actually gets its name due to its presence on the Silene acaulis plant! Not only was this fungus abundant in Silene leaves, but it was not present in the other two plant species’ leaves that I studied, highlighting it’s specificity to Silene, although it has also been reported in a couple of other arctic/alpine plant species (Steinke and Hyde 1997, Tojo et al. 2013). The community composition of leaf fungi (and bacteria too) was significantly different in the three plant species I studied, and this was partially driven by the abundance of P. silenes-acaulis in Silene acaulis and not the other two species (Figure 1). Statistical analysis showed that P. silenes-acaulis contributed 14% to differences in fungal communities between Silene and the bunchgrass Deschampsia, and 31% to differences in fungal communities between Silene and the edible alpine mountain sorrel plant Oxyria.
The genus Phaeosphaeria is in the phylum Ascomycota and contains saprotrophic fungi that function as decomposers. Sixteen different species in the genus have been previously reported in arctic and alpine ecosystems, including Svalbard, Norway and the Tatra Mountains in Slovakia (Tojo et al. 2013, Kozłowska et al. 2016). These fungi are adapted to these ecosystems by having a simple life cycle, forming thick and deeply pigmented walls, and having ascospores (reproductive spores produced by fungi in the Ascomycota phylum, Figure 2) with gelatinous sheaths (Leuchtmann 1987). Another species of note in the genus is Phaeosphaeria oryza, which associates with rice and is an important biological control agent of rice blast disease (Ohtake et al. 2008).
As with many microbial taxa, we have now done the basic ecological work of sequencing and phylogenetic classification, but information is lacking on function. As I have done with some of my root samples, future work could attempt to isolate this fungus by placing Silene acaulis leaves on petri dishes with agar and an energy source, and then do further experiments to examine the role of the fungus either in decomposition or Silene acaulis plant health.
Bueno de Mesquita C.P., Schmidt S.K., Suding K.N. (2019) Species-specific plant-microbe interactions in an early successional ecosystem. Plant and Soil in review.
Kozłowska M., Mułenko W., Bacigálová K, Wołczańska A., Świderska-Burek U., Pluta M. (2016) Microfungi of the Tatra Mountains. Part 7. Correction of some data from herbaria and the literature. Acta Mycologica 51(2):1081.
Leuchtmann A. (1987) Phaeosphaeria in the Arctic and Alpine Zones. In: Laursen G.A., Ammirati J.F., Redhead S.A. (eds) Arctic and Alpine Mycology II. Environmental Science Research, vol 34. Springer, Boston, MA
Ohtaka N., Kawamata H., Narisawa K. (2008) Suppression of rice blast using freeze-killed mycelia of biocontrol fungal candidate MKP5111B. Journal of General Plant Pathology 74: 101-108
Quaedvlieg W., Verkley G.J., Shin H.D., Barreto R.W., Alfenas A.C., Swart W.J., Groenewald J.Z., Crous P.W. (2013) Sizing up Septoria. Studies in Mycology 75: 307-390.
Tojo M., Masumoto S., Hoshino T. (2013) Phytopathogenic Fungi and Fungal-Like Microbes in Svalbard. In: Imai R., Yoshida M., Matsumoto N. (eds) Plant and Microbe Adaptations to Cold in a Changing World. Springer, New York, NY
Steinke T.D., Hyde K.D. (1997) Phaeosphaeria capensis sp. nov. from Avicennia marina in South Africa. Mycoscience 38: 101-103.
by Cliff Bueno de Mesquita
I have finished analyzing data from an experiment I did looking at how adding plant litter (dead leaves) affects microbial communities in unvegetated soils. Since microbial growth in unvegetated soils can be limited by carbon, and plant leaves contain lots of carbon, we expected to see changes in microbial communities as different microbes increase in growth to decompose the leaves. Besides that, leaves also harbor their own microbial communities, which also get added to soil when they fall. Botrytis caroliniana (Figure 1) is a species of fungus that was abundant in plant litter but also varied among plant species. B. caroliniana was especially abundant in the leaves of the mountain sorrel plant Oxyria digyna and less abundant in the grass Deschampsia cespitosa and the cushion plant Silene acaulis.
Botrytis is a relatively well studied fungal genus with 22 described species, which typically cause disease in plants (Williamson et al. 2007). Botrytis species can be both biotrophs (eating living material) or necrotrophs (eating dead tissues). Several books have been written about the genus, focusing on their negative effects on important crop species (Elad et al. 2007). For example, the species Botrytis cinerea is reported to cause gray mold disease on 200 crop species, including cabbage, lettuce, broccoli, beans, grapes, strawberries, raspberries, and blackberries (Figure 2, Williamson et al. 2007). Botrytis caroliniana gets its name because it was first isolated from blackberry in South Carolina (Li et al. 2012). It has also been reported to cause gray mold disease on strawberries in North Carolina (Fernández-Ortuño et al. 2012). It is closely related to Botrytis fabiopsis and Botrytis galanthina, which cause gray mold disease in broad bean and snowdrop plants (Li et al. 2012).
Clearly, fungi in this genus are pathogens that can have major impacts on wild plants and agricultural crops. The market size for anti-Botrytis products was estimated at $15-25 billion USD (Elad et al. 2007). Now that we know that Botrytis caroliniana is abundant on Oxyria digyna leaves, we can conduct more specific research on the role of this fungus in plant health and plant communities in the alpine.
Elad Y, Williamson B, Tudzynski P, Delen N (eds) (2007) Botrytis: Biology, Pathology and Control. Springer, Dordrecht, The Netherlands
Fernández-Ortuño D, Li XP, Wang F, Schnabel G (2012) First Report of Gray Mold of Strawberry Caused by Botrytis caroliniana in North Carolina. Plant Dis. doi: 10.1094/pdis-12-11-1018-pdn
Li X, Kerrigan J, Chai W, Schnabel G (2012) Botrytis caroliniana , a new species isolated from blackberry in South Carolina. Mycologia 103:650–658. doi: 10.3852/11-218
Williamson B, Tudzynski B, Tudzynski P, Van Kan JAL (2007) Botrytis cinerea: The cause of grey mould disease. Mol Plant Pathol 8:561–580. doi: 10.1111/j.1364-3703.2007.00417.x
by Cliff Bueno de Mesquita
We have started another round of microscopy here in the AMO. We are collaborating with the Suding Lab on understanding how nitrogen deposition and plant species interactions affect microbial communities. One aspect of the work, as in some of our other projects, is to quantify how much of the plant roots contain certain fungi. I have previously written about both arbuscular mycorrhizal fungi and dark septate endophytes, which are two groups of fungi that inhabit plant roots, but there is another – fine root endophytes – that I will tell you about today.
Fine root endophytes (FRE) are a newly classified group of fungi that are characterized by having very fine hyphae. FRE were once considered to be arbuscular mycorrhizal fungi until further genetic work was able to distinguish them. Morphologically, they can be distinguished by their very fine hyphae, which are less the 2 µm wide – that’s 0.002 millimeters. But with the help of the microscope we can view them and identify them as FRE. They look like little fine blue lines (because we stain them with a blue dye) running all throughout the plant roots (Figure 1). Several studies have suggested that FRE can help plants uptake phosphorus, which means they may be functionally similar to arbuscular mycorrhizal fungi. FRE were once thought to be the species Glomus tenue, now reclassified as Planticonsortium tenue, but now several different morphologies have been observed and it is likely that there are several different species of fine root endophytes.
FRE are distributed globally, have been reported in 53 plant families, and have been found in all major habitat types. As we and others continue to quantify the amount of FRE in various plant species and various environments, we can learn more about the ecology of this potentially important fungal group. Additionally, more experiments are needed to learn more about the functioning of FRE.
Orchard S, Hilton S, Bending GD, et al (2017a) Fine endophytes (Glomus tenue) are related to Mucoromycotina, not Glomeromycota. New Phytol 213:481–486. doi: 10.1111/nph.14268
Orchard S, Standish RJ, Dickie IA, et al (2017b) Fine root endophytes under scrutiny: a review of the literature on arbuscule-producing fungi recently suggested to belong to the Mucoromycotina. Mycorrhiza 27:619–638. doi: 10.1007/s00572-017-0782-z
Walker C, Gollotte A, Redecker D (2018) A new genus, Planticonsortium (Mucoromycotina), and new combination (P. tenue), for the fine root endophyte, Glomus tenue (basionym Rhizophagus tenuis). Mycorrhiza 28:213–219. doi: 10.1007/s00572-017-0815-7
By Eli Gendron
Diatoms are a unique life form that can be found in a wide range of environments, from the soils of the arctic and the some of the highest mountains in the world to freshwater lakes across the globe and throughout our oceans (Mann & Droop 1996). One of the characteristics that make diatoms so unique is the glass like shell they build out of silica which often leads them to have regular geometric shaped cells (see Figure 1). These single celled organisms often form colonies that take many forms such as the chains seen in Figure 1. Diatoms are almost always photosynthetic but several strains have been found to be capable of mixotrophy and heterotrophy, meaning they are capable of living off organic matter (Villanova et al. 2017; Tan & Johns 1996).
Figure 1. Image of Fragilaria capucina as seen under a microscope. Left: Image of Fragilaria capucina taken in Chico, Washington, USA; Chico Creek, 400x magnification, DIC – 13 Jul 2008. Right: Image of Fragilaria capucina taken in Bremerton, Washington, USA; Kitsap Lake, 1000x magnification, DIC – 11 Oct 2008. Images curated by http://www.algaebase.org/search/species/detail/?species_id=31451&distro=y#distro
Diatoms such as Fragilaria capucina are a common occurrence in freshwater habitats around the world; however, they tend be low in abundance in oligotrophic (low nutrient) ecosystems. When an ecosystem is exposed to more nutrients than naturally occur, usually through pollution such as nitrogen in fertilizer run off, it becomes eutrophic (abundant nutrients) leading to blooms of previously rare organisms. Fragilaria capucina is one such diatom that is highly resistant to pollution and can often be found thriving in eutrophic conditions (Rott et al. 1998). Armed with this type of knowledge we can monitor communities of easily obtainable species to use as indicators of ecosystem status including catching pollution early.
Mann, D.G. & Droop, S.J.M. (1996) Biodiversity, biogeography and conservation of diatoms. Hydrobiologia 336: 19-32
Rott E, Duthie HC, Pipp E. 1998. Monitoring organic pollution and eutrophication in the Grand River, Ontario, by means of diatoms. Can J Fish Aquat Sci 55:1443–1453.
Tan, C.K. and Johns, M.R., 1996. Screening of diatoms for heterotrophic eicosapentaenoic acid production. Journal of Applied Phycology, 8(1), pp.59-64.
Villanova, V., Fortunato, A.E., Singh, D., Dal Bo, D., Conte, M., Obata, T., Jouhet, J., Fernie, A.R., Marechal, E., Falciatore, A. and Pagliardini, J., 2017. Investigating mixotrophic metabolism in the model diatom Phaeodactylum tricornutum. Phil. Trans. R. Soc. B, 372(1728), p.20160404
by Cliff Bueno de Mesquita
Happy new year’s eve from all of us here at the AMO! I am writing this post from little Rhode Island (where I grew up), so I decided to write about a local microbe. So this month’s microbe is a genus called Phytophthera. Phytophthera is a type of microorganism called an oomycete, which is different from, say, a bacterium or a fungus. Oomycetes are often described as being quite similar to fungi, but they form their own unique lineage on the phylogenetic tree of life. They are filamentous, spore-producing organisms that often function as either saprotrophs (organisms that decompose organic matter), or plant pathogens, living on plants and causing them harm. Unlike fungi, whose cell walls are made of chitin, Phytophthera cell walls are made of cellulose. There are 232 described species and species variations in the genus, though it is estimated that there could be as many as 200-300 more that we have not discovered yet!
One of the most common tree diseases in Rhode Island is Phytophthera root rot, which occurs on beech trees. The Phytophthera oomycete in this case infests the beech tree roots, but infected trees will also show bleeding cankers on the trunks (Figure 1). Phytophthera root rot is a leading cause of death for older beech trees. But the Phytophthera genus is actually quite widespread and infects thousands of plant species, including important forest trees like chesnuts, oaks, and alders, and important crops such as strawberries, citrus trees, cucumbers, squash, soybeans, tomatoes and potatoes. Most notably, the species Phytophthera infestans caused the potato blight that led to the Great Irish Potato Famine of 1845-1849!
Goheen EM, Frankel SJ, eds. 2007. Phytophthoras in Forests and Natural Ecosystems. Albany, CA, USA: USDA Forest Service: General Technical Report PSW-GTR-221, 101–15. https://www.fs.fed.us/psw/publications/documents/psw_gtr221/psw_gtr221.pdf
Kaiser Tree Preservation Co. 2018. Top 10 Tree Diseases in Rhode Island. http://kaisertree.com/services/plant-health-care-2-2/top-10-tree-diseases-in-rhode-island/
NCBI. 2018. Phytopthera. NCBI taxonomy. Bethesda, MD: National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Tree&id=4783&lvl=3&keep=1&srchmode=1&unlock
Nowicki M, Foolad MR, Nowakowska M, Kozik EU. 2011. Potato and tomato late blight caused by Phytophthora infestans: An overview of pathology and resistance breeding. Plant Disease, 96: 4–17, doi:10.1094/PDIS-05-11-0458
by Cliff Bueno de Mesquita
I hope everyone had a wonderful Thanksgiving and gave thanks to all of the fascinating microorganisms that we depend on. For this post I’ll write about a fungus that I was recently able to culture (Figure 1). The green culture seen in Figure 1 is characteristic of the fungal genus Trichoderma. This culture was isolated from the inside of a root of a grass that I have been working with for the Moving Uphill project. I harvested the grasses that I transplanted into unvegetated soil 2 years ago to see what I could culture and isolate for potential follow up studies. Trichoderma is a ubiquitous soil fungus but recent studies have shown that it can also colonize plant roots (Harman et al. 2004, Bae et al. 2011).
Trichoderma is in the Hypocreaceae family, in the Ascomycota phylum. The taxonomy has been updated several times, but there are currently 89 species recognized in the genus (Samuels 2006). Trichoderma viride, perhaps the species I have in culture, was the first species described in the genus and is a green mold. Trichoderma aggressivum is another green mold that causes disease on cultivated button mushrooms (Samuels et al. 2002).
In soil, Trichoderma is a saprotroph, eating organic carbon in the form of dead plant and fungal material. Trichoderma produces enzymes to break this matter down, and humans have used Trichoderma to produce industrial amounts of decomposition enzymes like cellulase and chitinase (Felse and Panda 1999). Cellulase breaks down cellulose, the main ingredient of plant cell walls, while chitinase breaks down chitin, the main ingredient of fungal cell walls.
Inside of plant roots, the fungus produces a variety of compounds that can induce plant responses. Studies have shown that root colonization by Trichoderma frequently enhances root growth and development, plant productivity, resistance to abiotic stress, and nutrient uptake (Harman et al. 2004). Thus Trichoderma can be a very beneficial fungus for plants, but it has received much less attention than mycorrhizal fungi. It can be important for our crop plants too – Bae et al. (2011) found that Trichoderma helped delay disease in hot pepper plants. Perhaps it’s time for us to conduct some experiments with my cultures and see how they affect alpine plants!
Bae, H; Roberts, DP; Lim, HS; Strem, MD; Park, SC; Ryu, CM; Melnick, RL; Bailey, BA (2011). Endophytic Trichoderma isolates from tropical environments delay disease onset and induce resistance against Phytophthora capsici in hot pepper using multiple mechanisms. Mol. Plant Microbe Interact. 24: 336–51. doi:10.1094/MPMI-09-10-0221.
Felse, P.A, Panda, T. (1999). Taguchi Method. Enzyme and Microbial Technology. 40 (4): 801–805. doi:10.1016/j.enzmictec.2006.06.013.
Harman, G.E., Howell, C.R., Viterbo, A., Chet, I., Lorito, M. (2004). Trichoderma species—opportunistic avirulent plant symbionts. Nature Reviews Microbiology. 2 (1): 43–56. doi:10.1038/nrmicro797.
Samuels, G.J., Dodd, S.L., Gams, W., Castlebury, L.A., Petrini, O. (2002). Trichoderma species associated with the green mold epidemic of commercially grown Agaricus bisporus. Mycologia. 94 (1): 146–170.
Samuels, G.J. (2006). Trichoderma: Systematics, the Sexual State, and Ecology. Phytopathology. 96 (2): 195–206. doi:10.1094/PHYTO-96-0195.
by Cliff Bueno de Mesquita
I just finished another round of root microscopy! We are interested in the ecology of fungal endophytes and often look at roots under the microscope to quantify how much of the root is colonized by fungi. While I focus on dark septate endophytes and mycorrhizal fungi (see previous posts), which are typically beneficial for plants, I also sometimes come across some pathogens in the roots. One such pathogen is the genus Olpidium. This genus of fungi has been of interest the agricultural field, as one species, Olpidium brassicae, has been shown to be a disease vector in a wide variety of plants including cucumber and lettuce plants. The fungus can infect lettuce roots, and transmit lettuce big-vein disease through its zoospores, which are the motile, asexual spores that Olpidium reproduces with (Tomlinson and Faithfull 1979). Another species, Olpidium radicale was shown to transmit melon necrotic spot virus disease in cucumbers (Tomlinson and Thomas 1986). A third species, Olpidium virulentus, can transmit olive mild mosaic virus (Reis Varanda et al. 2015). Another virus, tobacco necrosis virus, was also shown to be transmitted by Olpidium brassicae zoospores. This virus affects at least 88 different plant species, including tobacco, soybeans, and olive trees (Díaz-Cruz et al. 2017). Yikes!
Fortunately for the alpine plants we study, Olpidium appears very rarely in their roots. Of the 35 plants we surveyed in 2016, only 5 of them contained Olpidium. When we do see it, the Olpidium cells are easily recognizable due to their distinct hexagonal shape (Figure 1). It remains unclear if this is an important pathogen for alpine plants or if it is causing them any harm.
Díaz-Cruz GA, Smith CM, Wiebe KF, Cassone BJ. 2017. First complete genome sequence of Tobacco necrosis virus Disolated from soybean and from North America. Genome Announce.5(32): e00781-17.
Tomlinson JA, Faithfull EM. 1979. Effects of fungicides and surfactants on the zoospores of Olpidium brassicae. Ann. appl. Biol.93: 13-19.
Tomlinson JA, Thomas BJ. 1986. Studies on melon necrotic spot virus disease of cucumber and on the control of the fungus vector (Olpidium radicale). Ann. appl. Biol.108: 71-80.
Reis Varanda CM, Santos SJ, Esteves da Clara MI, do Rosário F. Félix M. 2015. Olive mild mosaic virus transmission by Olpidium virulentus. Euro. J. Plant. Path. DOI: 10.1007/s10658-015-0593-z.
by Eli Gendron
Dinoflagellates are an extremely morphologically and ecologically diverse group of organisms. Dinoflagellates are mainly characterized by their two dissimilar flagella (whiplike appendages used for swimming), with a transverse flagella that beats to the side of the cell and a conventional flagella that beasts posteriorly, and a cell covering called an amphiesma or cortex (Figure 1a). Many dinoflagellates, such as Karenia brevis in particular, are capable of filling multiple ecological roles as they are capable of auxotrophic heterotrophy (meaning they can utilize both organic and inorganic compounds as food), as well as also possessing chloroplasts allowing them to perform photosynthesis as well (Figure 1b) [Vargo 2009]. Karenia brevis is most well-known for its role in harmful algae blooms (HABs) and is one of the primary organisms responsible for the phenomena known as ‘red tides’ seen off the Florida coast [Ross et al. 2010]. One of the reasons HABs of Karenia brevis are so disruptive to ecosystems is due to their ability to produce brevetoxins. Brevetoxins are neurotoxins produced by dinoflagellates such as Karenia brevis, and when their populations bloom during HABs, the concentration of these toxins can reach harmful and potentially deadly levels resulting in fish kills, coral death, and even human illness [Baden 1989]. Currently, it is not currently known for certain why Karenia brevis and other dinoflagellates produce brevetoxins. One of the more recent debates revolves around the hypothesis that brevetoxins are produced in response to osmotic stress felt by these organisms [Errera & Campbell 2011; Sunda et al. 2013].
Figure 1. Karenia brevis. Scanning election micrograph (a + c) of dorsal and ventral views highlights the two flagella and characteristic apical groove. Light microscopy (b + d) of Karenia brevis ventral view highlighting organelles (particularly chloroplasts). Scale bars, 10um. Figure adapted from [Haywood et al. 2004].
Baden, D. G. (1989). Brevetoxins: unique polyether dinoflagellate toxins. The FASEB journal, 3(7), 1807-1817.
Errera, R. M., & Campbell, L. (2011). Osmotic stress triggers toxin production by the dinoflagellate Karenia brevis. Proceedings of the National Academy of Sciences, 108(26), 10597-10601.
Haywood, A. J., Steidinger, K. A., Truby, E. W., Bergquist, P. R., Bergquist, P. L., Adamson, J., & Mackenzie, L. (2004). COMPARATIVE MORPHOLOGY AND MOLECULAR PHYLOGENETIC ANALYSIS OF THREE NEW SPECIES OF THE GENUS KARENIA (DINOPHYCEAE) FROM NEW ZEALAND 1. Journal of Phycology, 40(1), 165-179.
Ross, C., Ritson-Williams, R., Pierce, R., Bullington, J. B., Henry, M., & Paul, V. J. (2010). Effects of the Florida red tide dinoflagellate, Karenia brevis, on oxidative stress and metamorphosis of larvae of the coral Porites astreoides. Harmful Algae, 9(2), 173-179.
Sunda, W. G., Burleson, C., Hardison, D. R., Morey, J. S., Wang, Z., Wolny, J., ... & Van Dolah, F. M. (2013). Osmotic stress does not trigger brevetoxin production in the dinoflagellate Karenia brevis. Proceedings of the National Academy of Sciences, 110(25), 10223-10228.
Vargo, G. A. (2009). A brief summary of the physiology and ecology of Karenia brevis Davis (G. Hansen and Moestrup comb. nov.) red tides on the West Florida Shelf and of hypotheses posed for their initiation, growth, maintenance, and termination. Harmful Algae, 8(4), 573-584.
Various lab members contribute to the MoM Blog