scholarly journals High Arctic biocrusts: characterization of the exopolysaccharidic matrix

Polar Biology ◽  
2020 ◽  
Vol 43 (11) ◽  
pp. 1805-1815
Author(s):  
Gianmarco Mugnai ◽  
Federico Rossi ◽  
Cristina Mascalchi ◽  
Stefano Ventura ◽  
Roberto De Philippis
Keyword(s):  
Molecular Weight ◽  
Soil Stabilization ◽  
Developmental Stages ◽  
Heterotrophic Bacteria ◽  
Microbial Community Composition ◽  
High Arctic ◽  
Polymeric Matrix ◽  
Freezing Stress ◽  
Glacier Terminus ◽  
Moss Crusts

Abstract Biocrusts can be found in a wide array of habitats, where they provide important ecosystem services. These microbial associations are particularly important in High Arctic environments, where biocrust colonize the newly exposed barren soil after glacier retreat and significantly contribute to soil stabilization and nutrient cycling. Starting from incipient, structurally simple biolayers, they develop in complexity, increasing from the glacier terminus. Starting from a simple community structure, mainly constituted by cyanobacteria, heterotrophic bacteria and fungi immersed in a self-secreted extracellular polymeric matrix (cyanobacterial crusts), they later may recruit mosses and lichens (moss crusts and lichen crusts, respectively). The extracellular polymeric matrix protects the biocrust community from abiotic constraints, notably drought and freezing stress, from external physical harming factors, and from predation. The physicochemical characteristics of the extracellular matrix are related to several of its properties, such as its soil-stabilizing effect and water retention. We analysed the chemical (monosaccharidic composition) and macromolecular (molecular weight distribution) properties of the extracellular polymeric matrix of biocrusts with different morphologies collected in northwestern Spitsbergen, Norway. The uronic acid content and molecular weight (MW) distribution of the extracellular polysaccharidic matrices (EPMs) appeared in accordance with the developmental stages of the biocrusts. The MW distribution also showed significant differences between the samples, possibly reflecting differences in microbial enzymatic activities leading to the degradation of high-MW polymers into smaller compounds. The MW distribution profiles presented some important differences, reflecting differences in environmental conditions and, probably, the seasonal variance in microbial community composition that is known to characterize the environment examined in the present study.

scholarly journals On the chemical dynamics of extracellular polysaccharides in the high Arctic surface microlayer

Ocean Science ◽  
2012 ◽  
Vol 8 (4) ◽  
pp. 401-418 ◽  
Author(s):  
Q. Gao ◽  
C. Leck ◽  
C. Rauschenberg ◽  
P. A. Matrai
Keyword(s):  
Molecular Weight ◽  
Organic Matter ◽  
Compositional Analysis ◽  
Physicochemical Characteristics ◽  
High Arctic ◽  
The Arctic ◽  
Extracellular Polysaccharides ◽  
Surface Microlayer ◽  
Biological Origin ◽  
Ocean Study

Abstract. The surface microlayer (SML) represents a unique system of which the physicochemical characteristics may differ from those of the underlying subsurface seawater (SSW). Within the Arctic pack ice area, the SML has been characterized as enriched in small colloids of biological origin, resulting from extracellular polymeric secretions (EPS). During the Arctic Summer Cloud Ocean Study (ASCOS) in August 2008, particulate organic matter (POM, with size range > 0.22 μm) and dissolved organic matter (DOM, < 0.22 μm, obtained after filtration) samples were collected and chemically characterized from the SML and the corresponding SSW at an open lead centered at 87.5° N and 5° E. Total organic carbon was persistently enriched in the SML with a mean enrichment factor (EF) of 1.45 ± 0.41, whereas sporadic depletions of dissolved carbohydrates and amino acids were observed. Monosaccharide compositional analysis reveals that EPS in the Arctic lead was formed mainly of distinctive heteropolysaccharides, enriched in xylose, fucose and glucose. The mean concentrations of total hydrolysable neutral sugars in SSW were 94.9 ± 37.5 nM in high molecular weight (HMW) DOM (> 5 kDa) and 64.4 ± 14.5 nM in POM. The enrichment of polysaccharides in the SML appeared to be a common feature, with EFs ranging from 1.7 to 7.0 for particulate polysaccharides and 3.5 to 12.1 for polysaccharides in the HMW DOM fraction. A calculated monosaccharide yield suggests that polymers in the HMW DOM fraction were scavenged, without substantial degradation, into the SML. Bubble scavenging experiments showed that newly aggregated particles could be formed abiotically by coagulation of low molecular weight nanometer-sized gels. Aerosol particles, artificially generated by bubbling experiments, were enriched in polysaccharides by factors of 22–70, relative to the source seawater. We propose that bubble scavenging of surface-active polysaccharides could be one of the possible mechanisms for the enrichment of polysaccharides in the high Arctic open lead SML.

scholarly journals Milne Glacier, Northern Ellesmere Island, N.W.T., Canada: a Surging Glacier?

1984 ◽  
Vol 30 (105) ◽  
pp. 251-253 ◽  
Author(s):  
Martin O. Jeffries
Keyword(s):  
Critical Condition ◽  
Maximum Rate ◽  
High Arctic ◽  
Ellesmere Island ◽  
Accumulation Rates ◽  
Reservoir Area ◽  
Ice Caps ◽  
Glacier Terminus ◽  
Valley Glacier ◽  
Glacier Surges

AbstractDuring the period 1966 to 1983 Milne Glacier advanced 4.25 km at a mean annual rate of 250 m a−1. Since surges commonly occur over a two or three year period the maximum rate of advance could have been greater than 2 km a−1. The glacier terminus has a number of features indicative of past surge behaviour. Of these, at least three looped moraines suggest surges of the main valley glacier and tributary glaciers. As Milne Glacier is a cold glacier, surges may possibly be thermally regulated Accumulation rates on the ice caps of northern Ellesmere Island are low hence a critical condition in the “reservoir area” will be only slowly attained. As a consequence the periodicity of surges in Milne Glacier and other High Arctic glaciers is expected to be high.

A reinvestigation of collared flagellates in the genus Bicosta Leadbeater with special reference to correlations with climate

1980 ◽  
Vol 290 (1041) ◽  
pp. 431-447 ◽  
Keyword(s):  
Developmental Stages ◽  
High Arctic ◽  
The Arctic ◽  
Spine Length ◽  
Slowing Down ◽  
Environmental Selection ◽  
Taxonomic Descriptions ◽  
New Information ◽  
New Findings ◽  
Mode Of Attachment

By combining light microscopy and electron microscopy, the range of geographically linked diversity in lorica size and construction has been recorded for each of the three species of Bicosta , on the basis of wild material processed directly from the sea, in many different parts of the world distributed from the high Arctic to the Equator and further south. Characteristic differences in responses to climatic pressures occur. The least sensitive species is B. minor , present throughout the temperature range ( - 1 to 22 °C), but with local differences of size depending on environmental factors other than temperature, the smallest cells having been recorded in south (but not north) Alaska and the largest at Portsmouth (England) and in the Galapagos Islands. The other two species are less tolerant of high temperatures and have not been found above 16 °C though they have crossed the Equator. Both are common in the Arctic, where the largest cells characteristically occur. The most elaborate responses were found in B. spinifera; these apparently resulted from two different factors, namely environmental selection among genetically predetermined biotypes differing in cell size, and environmentally induced local modifications, probably caused by the slowing down of critical developmental stages under the action of cold. The exaggerated spine length compared with cell length, characteristic of many large arctic specimens, is interpreted in this way, the critical stages involved being late in the replication cycle since both in B. minor and B. spinifera the costal strips formed first are the short ones. Other biologically significant observations include new information on the structure of the membrane subtending the protoplast and on its mode of attachment to the lorica, which is different in each of the species. Revised taxonomic descriptions summarizing selected parts of the new findings are given at the end of the paper.

scholarly journals Mapping thermal and hydrological conditions beneath a polythermal glacier with radio-echo sounding

2001 ◽  
Vol 47 (157) ◽  
pp. 232-242 ◽  
Author(s):  
Luke Copland ◽  
Martin Sharp
Keyword(s):  
Thermal Structure ◽  
Basal Layer ◽  
Equipotential Surface ◽  
High Arctic ◽  
Hydrological Conditions ◽  
Glacier Terminus ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
Polythermal Glacier ◽  
Echo Sounding

AbstractSpatial patterns in residual bed reflection power (BRPr), derived from ground-based radio-echo sounding, were mapped and interpreted in terms of the thermal and hydrological conditions at the base of a high-Arctic polythermal glacier (John Evans Glacier, Ellesmere Island, Canada). BRPr is the residual from a statistical relationship between measured bed reflection power and ice thickness that describes the rate of dielectric loss with depth in the glacier. We identified three types of thermal structure: (a) Positive BRPr and an internal reflecting horizon occur over the glacier terminus. The reflecting horizon is interpreted as the boundary between warm and cold ice, and suggests the presence of a warm basal layer. (b) Positive BRPr occurs without an internal reflector in the upper part of the ablation zone. This suggests that ice is at the pressure-melting point only at the bed. (c) Negative BRPr without an internal reflector occurs in all other regions, suggesting cold ice at the bed. Where BRPr is positive, its pattern is similar to the pattern of subglacial water flow predicted from the form of the subglacial hydraulic equipotential surface. This suggests that hydrological conditions at the glacier bed are a major control on BRPr, probably because the dielectric contrast between ice and water is higher than that between ice and other subglacial materials.

scholarly journals Microbial dynamics in a High-Arctic glacier forefield: a combined field, laboratory, and modelling approach

2016 ◽  
Author(s):  
James A. Bradley ◽  
Sandra Arndt ◽  
Marie Šabacká ◽  
Liane G. Benning ◽  
Gary L. Barker ◽  
...  
Keyword(s):  
Microbial Community ◽  
Numerical Model ◽  
Microbial Communities ◽  
Community Dynamics ◽  
Heterotrophic Bacteria ◽  
High Arctic ◽  
Soil Development ◽  
Arctic Soils ◽  
Field Laboratory ◽  
Modelling Approach

Abstract. Modelling the development of soils in glacier forefields is necessary in order to assess how microbial and geochemical processes interact and shape soil development in response to glacier retreat. Furthermore, such models can help us predict microbial growth and the fate of Arctic soils in an increasingly ice-free future. Here, for the first time, we combined field sampling with laboratory analyses and numerical modelling to investigate microbial community dynamics in oligotrophic proglacial soils in Svalbard. We measured low bacterial growth rates and growth efficiencies (relative to estimates from Alpine glacier forefields), and high sensitivity to soil temperature (relative to temperate soils). We used these laboratory measurements to inform parameter values in a new numerical model and significantly refined predictions of microbial and biogeochemical dynamics of soil development over a period of roughly 120 years. The model predicted the observed accumulation of autotrophic and heterotrophic biomass. Genomic data indicated that initial microbial communities were dominated by bacteria derived from the subglacial environment, whereas older soils hosted a mixed community of autotrophic and heterotrophic bacteria. This finding was validated by the numerical model, which showed that active microbial communities play key roles in fixing and recycling carbon and nutrients. We also demonstrated the role of allochthonous carbon and microbial necromass in sustaining a pool of organic material, despite high heterotrophic activity in older soils. This combined field, laboratory and modelling approach demonstrates the value of integrated model-data studies to understand and quantify the functioning of the microbial community in an emerging High-Arctic soil ecosystem.

scholarly journals Identifying drivers of microbial community composition associated with aquatic primary producers: metagenomic analysis of cyanobacterial cultures

2020 ◽  
Vol 2 (7A) ◽  
Author(s):  
David Green ◽  
Cecilia Rad-Menendez ◽  
Frederik De Boever
Keyword(s):  
Community Composition ◽  
Life Support ◽  
Heterotrophic Bacteria ◽  
Microbial Community Composition ◽  
Culture Collection ◽  
Taxonomic Composition ◽  
Metagenomic Analysis ◽  
Primary Producers ◽  
Functional Variation ◽  
Core Microbiome

The energy derived from aquatic primary production is fundamental to driving Earth’s life support systems – but they don’t achieve all this by themselves. Heterotrophic bacteria found in the photic zones of aquatic environments have a fundamental role in this too. Our group’s interest is in understanding how heterotrophs help autotrophs: who in these communities are important, and how and why they are important. Answering this is important in both natural and manmade environments so we can model these environments, and as appropriate, manipulate them, such as applying designer microbiomes to aid industrialisation of algal cultivation. Metagenomic analysis of 31 marine and freshwater cyanobacterial cultures from the Culture Collection of Algae & Protozoa resulted in assembly of >400 bacterial metagenomes (MAGs) with ca. 14 unique MAGs per culture. Community composition was clearly partitioned by salinity as a driver but collectively niche accounted for most community taxonomic variation. No universal core microbiome was identified, but taxonomic composition of marine cultures bore notable similarities to marine eukaryotic algal communities and to a natural cyanobacterial mat community found next to a northern Chilean geyser. Stable taxonomic associations imply that these taxa may have functional importance to their algal host. Functional analysis of the MAGs is underway and we will test whether the relative taxonomic variability contrasts with low functional variation between communities. If true, this implies that primary producers drive community assembly in a functionally predictable way, and that function, not taxonomy, is the more important parameter to understand.

On the mechanical and morphological properties of highly performant composite laminates based on epoxy resin and oxidized ultrahigh-molecular-weight polyethylene fibers

2020 ◽  
Vol 32 (9) ◽  
pp. 992-1000 ◽  
Author(s):  
Raouf Belgacemi ◽  
Mehdi Derradji ◽  
Abdelrazak Mouloud ◽  
Djalal Trache ◽  
Abdeldjalil Zegaoui ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Epoxy Resin ◽  
Composite Laminates ◽  
High Performance ◽  
Ultrahigh Molecular Weight Polyethylene ◽  
Cost Effective ◽  
Polymeric Matrix ◽  
Morphological Properties ◽  
Ultrahigh Molecular Weight ◽  
Uhmwpe Fibers

In this study, new high-performance composite laminates were prepared from epoxy resin and surface modified ultrahigh-molecular-weight polyethylene (UHMWPE) fibers. The UHMWPE fibers underwent two types of chemical modifications, namely through chromic acid and potassium permanganate oxidations. The adopted chemical procedure aimed the grafting of polar groups on the outer surface of fibers for an improved chemical and physical compatibility with the polymeric matrix. The efficiency of the grafting methodology was confirmed by vibrational, thermal, and morphological analyses, and the grafting mechanism was thoroughly discussed. Furthermore, composite laminates were prepared to study the effects of chemical treatments on the mechanical and morphological properties of the resulting composites. The grafting techniques allowed consequent improvements in the tensile and bending properties, up to 34% and 23% for the tensile and flexural strengths, respectively. The study of the fractured surfaces confirmed the exceptional compatibility between the fillers and the polymeric matrix and further corroborated the mechanical findings. Finally, the adopted modification techniques can be regarded as cost-effective and highly suitable for the manufacturing of structural composites for advanced applications.

Yolk proteins in salmon (Salmo salar) oocytes, eyed eggs, and alevins differing in viability

1990 ◽  
Vol 68 (5) ◽  
pp. 895-900 ◽  
Author(s):  
Thomas Olin ◽  
Alexandra von der Decken
Keyword(s):  
Molecular Weight ◽  
Salmo Salar ◽  
Gel Electrophoresis ◽  
Developmental Stages ◽  
Polyacrylamide Gel Electrophoresis ◽  
Specific Antigen ◽  
Protein Composition ◽  
Polyacrylamide Gel ◽  
Parental Origin ◽  
Yolk Proteins

The developmental stages of oocytes, eyed eggs, and alevins from salmon (Salmo salar) were compared for their yolk protein composition. In oocytes, SDS–polyacrylamide gel electrophoresis showed high amounts of a protein with the molecular weight (Mr) of 94 000. In eyed eggs, the 94 000 protein decreased and was undetectable in the alevins. Furthermore, in eyed eggs the proteins of 67 000, 30 000, and 27 000 increased, while in the alevins the concentration of the 67 000 protein decreased and that of the 39 000 increased. Vitellogenin-specific antigen sites analyzed by immunoblotting were most pronounced with the proteins of 94 000, 67 000, 39 000, 30 000, 23 000, and 19 000. Separation of the yolk proteins by HPLC gave four peaks at 280 nm for all three developmental stages. Each peak consisted of several proteins as analyzed by SDS–polyacrylamide gel electrophoresis. The 7-day-old alevins sampled from groups of different parental origin showed differences in the amount of the 67 000 and 23 000 proteins. Expectancy of survival within the group in connection with a slow disappearance of the 67 000 and 23 000 proteins was statistically significant. A fast disappearance may be used as an indication of, but not as the reason for, a high mortality within one group of alevins.

Sign in / Sign up

Export Citation Format

Share Document