by Cliff Bueno de Mesquita
Hello! This month’s microbe the genus Entrophospora. Entrophospora is an arbuscular mycorrhizal fungus (AMF). What does that mean? A mycorrhizal fungus is any fungus that grows on or inside of plant roots and directly interacts with the plant in some capacity, typically nutrient exchange. There are several different types of mycorrhizae such as:
Ectomycorrhizae- which live on the outside of plant roots and are common associates of many tree species.
Ericoid mycorrhizae- which associate with plants in the Ericaceae family such as blueberries and cranberries.
Dark septate endophytes- which are described in detail in the April 2017 post below.
Arbuscular mycorrhizae live on the inside of plant roots and their defining feature is the formation of treelike structures called arbuscules (Figure 1). Arbuscules are the site of active two-way transfers of nutrients between the plant host and the fungus(1). All arbuscular mycorrhizae are in the phylum Glomeromycota(2), which is a separate phylum from typical edible mushrooms you may eat (typically Ascomycota or Basidiomycota).
Figure 1. AMF structures inside a plant root. Panel A shows blue stained hyphae invading the brick-like plant root, and 2 arbuscules. Panel B is a blown-up image of an arbuscule. Panel A taken from https://mycorrhizas.info/vam.html; Panel B taken from http://www.gpnmag.com/article/mycorrhizae-description-of-types-benefits-and-uses/ .
Entrophospora was the most abundant of the 28 AMF genera that we found in our 2016 Colorado root samples, based on DNA analysis. We found DNA matching Entrophospora in 27 plant samples. Entrophospora, like other AMF at our sites, is likely helping plants acquire phosphorus. Previous work in our lab showed correlations between arbuscules and plant phosphorus levels1, which supports this suggestion. Undeveloped soil, typical in high elevation sites recently exposed by receding glaciers, is often very limited in phosphorus, as it is still locked up in bedrock and has not had time to become available(3).
(1) Mullen RB & Schmidt SK. 1993. Mycorrhizal infection, phosphorus uptake, and phenology in Ranunculus adoneus: implications for the functioning of mycorrhizae in alpine systems. Oecologia 94:229-234.
(2) Schüßler A, Schwarzott D, and Walker C. 2001. A new fungal phylum, the Glomeromycota: phylogeny and evolution. Mycological Research 105(12):1413-1421.
(3) King AJ, Meyer AF, and Schmidt SK. 2008. High levels of microbial biomass and activity in unvegetated tropical and temperate soils. Soil Biology & Biochemistry 40:2605-2610.
By Pacifica Sommers
This month’s microbe, Paramecium putrinum, is a ciliate. Ciliates are single celled animals, but can be large by microbial standards: many of them that I have observed are more than 100 µm long. That may sound small, but it is 50 times larger than most bacteria, which are usually less than 5 um (Kubitschek et al. 1993), and 5-10 times larger than most human cells, which are 10-20 µm (Barrandon et al. 1985). Ciliates are more like a human cell than a bacterium because their DNA is encased inside an envelope-like membrane in a nucleus (actually in many nuclei, Lee et al. 2000) inside the cell, which bacteria do not have.
Ciliates generally eat other organisms, including algae, bacteria, and even other ciliates (Lee et al. 2000). They get the name “ciliate” from the hair-like cilia, structures that beat like tiny oars to propel the cell gracefully through water – even the small amounts of water between grains of soil! Ciliates live in all kinds of environments, from inside humans (yuck), to soils, to ephemeral rock pools on top of volcanoes, and even on glaciers (personal observation!).
An example of a ciliate (fig. 1) you may have seen in biology class is Paramecium multinucleatum. Why, you might wonder, is a lab focused on uncultured wild microbes in alpine soils writing about a Paramecium? Well, Paramecium putrinum, a cousin of sorts of the common “lab rat” P. multinucleatum, turned up in Antarctic cryoconite holes! Cryoconite holes are mud puddles that melt into glaciers. You can learn more about our research in Antarctic cryoconite holes at cryoholes.wordpress.com.
Mieczan and colleagues (2013) found P. putrinum in 30-40% of the cryoconite holes on a coastal Antarctic glacier, both in the sediment at the bottom of the hole and at the top. Having watched many a “lab rat” Paramecium cruising around a petri dish, their wide distribution inside the cryoconite holes does not surprise me. Having tried freezing and resuscitating my cultures of Paramecium multinucleatum, however, the ability of this species to live in Antarctica is surprising! Cryoconite holes there definitely freeze solid during the long, dark winter, so P. putrinum must have freeze-tolerant abilities that its lab rat cousin lacks.
We find a few DNA sequences that map most closely to Paramecium in cryoconite holes in a dry valley of Antarctica (fig. 2-3), on the far side of the continent from where Mieczan and colleagues sampled. Although ciliates in general are some of our most abundant DNA there, Paramecium is not the most common – but it might be a similar Paramecium to the one Mieczan found!
Barrandon, Y. and Green, H., 1985. Cell size as a determinant of the clone-forming ability of human keratinocytes. Proceedings of the National Academy of Sciences, 82(16), pp.5390-5394.
Kubitschek, H.E., 1990. Cell volume increase in Escherichia coli after shifts to richer media. Journal of bacteriology, 172(1), pp.94-101.
Lee, J.J., Huntner, S.H. and Bovee, E.C., 2000. An illustrated guide to the protozoa, Second Ed. Society of Protozoologists.
Mieczan, T., Górniak, D., Świątecki, A., Zdanowski, M. and Tarkowska-Kukuryk, M., 2013. The distribution of ciliates on Ecology Glacier (King George Island, Antarctica): relationships between species assemblages and environmental parameters. Polar Biology, 36(2), pp.249-258.
By Cliff Bueno de Mesquita
Hello! Thanks for checking out the AMO’s new microbe of the month blog. Each month we’ll write something about one of the cool microbes that we are studying.
This month’s microbe is a fungus by the name of Phialocephala fortinii, which we have been finding in our examination of microbes living on the roots of alpine plants in the Rocky Mountains, Colorado, USA. We sampled roots from 31 different plant species across an elevational gradient encompassing tundra meadows all the way up to sparsely vegetated rocky habitats by the continental divide. We looked at roots under the microscope and were able to see a number of different types of fungi including dark septate fungi (Figure 1).
Phialocephala is a genus of dark septate fungi, which get their name because of the dark brown color of their hyphae - filamentous, root-like fungal structures. The hyphae are also broken into segments, hence the name “septate” (Figure 1). This fungus appears to be an important mutualist with several alpine and polar plants, including pine trees, sedges, grasses, and rhododendron. In a mutualistic relationship, both parties benefit. In beneficial plant-fungal relationships, typically the plant gives the fungus carbon, and the fungus in exchange gives the plants nutrients such as nitrogen or phosphorus. In particular, research has shown that plants grown with Phialocephala fortinii on their roots have increased plant growth (biomass) as well as higher concentrations of nitrogen and phosphorus in the plant leaves, compared to plants grown without the fungus (Newsham, 2011). This suggests that the fungus does indeed help the plant acquire these nutrients, which is important for survival in the arctic and alpine.
Newsham, K. K. (2011). A meta-analysis of plant responses to dark septate root endophytes. New Phytologist, 190(3), 783–793. http://doi.org/10.1111/j.1469-8137.2010.03611.x
Schmidt, S. K., Sobieniak-Wiseman, L. C., Kageyama, S. a., Halloy, S. R. P., & Schadt, C. W. (2008). Mycorrhizal and Dark-Septate Fungi in Plant Roots Above 4270 Meters Elevation in the Andes and Rocky Mountains. Arctic, Antarctic, and Alpine Research, 40(3), 576–583. http://doi.org/10.1657/1523-0430(07-068)