PSA Didymo

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Information about PSA Didymo

Published on January 4, 2008

Author: Nellwyn


Slide1:  Michael R. Gretz1, Sarah N. Kiemle1, Michelle L. Riccio1, Tendeukai R. Hungwe1, Holly M. Burger1, Melba D. Apoya1, Sarah A. Spaulding2, and David S. Domozych3 1Biotechnology Research Center / Dept. of Biological Sciences, Michigan Technological University, Houghton, MI 49931, 2U.S. Geological Survey / EPA Region VII, Denver, CO 80202 3Department of Biology, Skidmore College, Saratoga Springs, NY 12866 Much of the impact of D. geminata is due to the production of prodigious amounts of extracellular polymers organized into stalks. The capability to secrete large quantities of highly organized extracellular polymer arrays differentiates D. geminata from other related benthic diatoms. Preliminary observations of the stalk of D. geminata indicate a relationship to those of the closely related benthic diatoms Cymbella and Gomphonema. These stalks are terminated in adhesive pads which attach the stalks to the substrata. From this pad structure the cell propagates stalk material until cell undergoes mitosis. Stalks bifurcate at the point of cell division as each daughter cell continues to produce stalk. Pads have not been examined in detail in freshwater diatoms, although the pads of marine Achnanthes longipes have been dissected chemically to some degree. Pads are primarily proteoglycan and are related chemically to the material produced during motility (Wustman et al. 1998). The primary polysaccharide component of the extracellular polymers of species closely related to D. geminata, Cymbella mexicana (Wustman et al 1997), Cymbella cistula (Wustman et al. 1997), and Gomphonema olivaceum (Huntsman and Sloneker 1971) was a sulfated xylogalactan. This sulfated polymer was in some ways structurally similar to agars and carrageenans reported from marine and freshwater red algae (Youngs et al. 1998). The sulfated xylogalactan from C. cistula was shown to be intrinsically hydrophilic and ionic cross bridging with Ca2+ was indicated. Based on preliminary results, D. geminata stalk may have similar structure to those of C. cistula. Didymosphenia geminata is a invasive species historically found only in alpine and boreal climates distinctly in the Northern Hemisphere in areas with low nitrogen, low phosphate, low temperature, and high light where it grew in patchy tufts in stream benthos and in lakes. D. geminata has now spread to encompass such areas as western North America, northern Europe, and New Zealand where it thrives in higher N up to 4 mg/L, temperature from 0-14oC and high light (Fig 1 A, C). This nuisance diatom forms massive growths (more than 30 cm thick), which cover benthic surfaces in streams for several kilometers (Fig 1 B). Mats of stalks trap D. geminata cells, other organisms, sediments, and provide attachment substrata for many different types of epiphytic diatoms (Fig 2 A,B). Most notably these stalk mats accumulate and cause masses resembling raw sewage, clog water intakes, and generally create negative impact. D. geminata colonizes and dominates the biomass of a given area, which has profound ramifications for the affected ecosystem. In areas dominated by D. geminata, it has been found that dense stalk mats decrease the amount of dissolved oxygen in the water, which has caused macroinvertebrate populations such as Ephemeroptera, Plecoptera, and Tricoptera to diminish substantially (Shelby 2006). Since the diet of young trout is predominantly comprised of macroinvertebrates, brown trout populations in Colorado and Arkansas have declined as well. Another factor which may have contributed to the decrease in the trout populations is that the mats of stalks decrease the area conducive for spawning (Shelby 2006). Discussion The ecological impact of the invasive diatom Didymosphenia geminata is highly significant in North America and New Zealand. The harmful algal blooms are affecting many stream environments. The frequency and extent of the large stalk mats has increased dramatically over the last few years. Significant blooms have been reported from Victoria Island to Virginia in North America and Biosecurity New Zealand is waging war on this invasive species which has significantly impacted streams of the south island. The large mats affect streams by trapping D. geminata cells, other organisms and sediments, and create unsightly masses resembling raw sewage, clog water intakes and generally create negative impact (Fig 1B). The mats of stalk are an excellent habitat for benthic algae, which use the stalk mats as an attachment substrate and consequently produce their own EPS into the environment. These stalk mats are created when D. geminata cells divide with concomitant stalk bifurcation, thereby producing long continuous interwoven stalk filaments stemming from one primary attachment point. Stalks are multi-laminate with a unique external layer and a more diffuse central area. The shaft is bounded by an outer laminated sheet that is made up of fibers connected by a smaller meshwork (Fig 4A). The most internal region of the stalk consist of fiber bundles (Fig 4D). External layers do not stain with Alcian Blue, indicating that sulfate or uronic acid components may not be present in these layers. The internal longitudinal striations of the stalk (Fig 4C) stain for sulfate and uronic acids and are crosslinked as shown with cytochemical staining. The stalk is composed primarily of sulfated polysaccharides with significant uronic acid content and protein. Sequential extraction of stalks yielded significant EDTA soluble material though it did not result in complete dissolution. Monosaccharide analysis revealed galactose and xylose as the most prevalent saccharides. Linkage analysis showed predominately 3,4-Gal and 4-Xyl. This, plus the presence of sulfate, leads to the hypothesis that the polysaccharide portion of the stalks is a sulfated xylogalactan, which has been reported for stalks of Cymbella and Gomphonema. Significant quantities of uronic acid were also detected. . References Baylson, F.A., Stevens, B.W. and Domozych, D.S. (2001) J. Phycol. 37: 796- 80. Domozych, D.S., Kort, S., Benton, S. and Yu, T. (2005) Biofilms 2: 1-16. Wustman BA, Gretz MR, Hoagland KD. (1997). Plant Physiol. 113:1059-1069. Wustman, B.A., Lind, J., Wetherbee, R., Gretz, M.R., 1998, Plant Physiology 116: 1431-1441. Shelby, EL (2006). Department of Environmental Quality Water Planning Division. Unpublished Report. Huntsman SA and Sloneler JH (1971). J. Phycol 7: 261-264.. Craigie J S, Wen, Z C & van der Meer J P 1984.. Bot. Mar. 27:55-61 Youngs, H.L., Gretz, M.R., West, J.A. & Sommerfeld, M.R. 1998. Phycological Research 46: 63-73. Bitter T, Muir HM (1962) A modified uronic acid carbazole reaction. Anal Biochem 4: 330-334. Methods Stalk material was collected from Boulder Creek in Boulder, Colorado. Samples were cleaned with forceps to remove macro invertebrates and organic debris, as well as sonicated and filtered to remove dirt, debris, and remnant frustules. Variable-pressure scanning electron microscopy (VPSEM) and transmission electron microscopy (TEM) processing followed the protocols employed in Baylson et al. (2001) and Domozych et al. (2005). Stalk fraction protocol was derived from Wustman et al. (1997). Carbohydrate, sulfate, protein, and uronic acid determinations followed the protocols of Dubois et al. (1956), Craigie et al. (1984) and Bitter and Muir (1962). Monosaccharide composition, linkage analyses, and cytochemical lectin-labeling were performed as in Wustman et al (1997). Fig 2. VPSEM images of D. geminata stalk mats from Boulder Creek.. A) Stalk mats with attached epiphytic diatoms, other organisms and debris held in the mats by extracellular polymeric substances (EPS). B) High magnification of girdle and valve views of D. geminata cells with attached stalks. The stalks of the D. geminata often times are heavily colonized with diatoms and other benthic organisms. 500nm 200 nm 2m A Fresh Look at an Invasive Species, Didymosphenia geminata: Chemical and Structural Analysis of the Extracellular Polymers

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