Fungal extracellular enzyme activity

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Extracellular

biopolymers
.

Plant residues, animals and microorganisms enter the dead

proteases)[4] and break them down into soluble sugars that are subsequently transported into cells to support heterotrophic metabolism.[1]

Biopolymers are structurally complex and require the combined actions of a community of diverse microorganisms and their secreted exoenzymes to depolymerize the polysaccharides into easily assimilable

heterotrophic soil microorganisms is essential for nutrient turnover and energy transfer in terrestrial ecosystems.[5] Exoenzymes also aid digestion in the guts of ruminants,[6] termites,[7] humans and herbivores. By hydrolyzing plant cell wall polymers, microbes release energy that has the potential to be used by humans as biofuel.[8] Other human uses include waste water treatment,[9] composting[10] and bioethanol production.[11]

Factors influencing extracellular enzyme activity

Extracellular enzyme production supplements the direct uptake of nutrients by microorganisms and is linked to nutrient availability and environmental conditions. The varied chemical structure of

upregulated when the substrate is abundant.[13]
This sensitivity to the presence of varying concentrations of substrate allows fungi to respond dynamically to the changing availability of specific resources. Benefits of exoenzyme production can also be lost after secretion because the enzymes are liable to denature, degrade or diffuse away from the producer cell.

Enzyme production and secretion is an energy intensive process

genes for extracellular enzymes and is adapted to degrade specific substrates.[12] In addition, the expression of genes that encode for enzymes is typically regulated by the availability of a given substrate. For example, presence of a low-molecular weight soluble substrate such as glucose will inhibit enzyme production by repressing the transcription of associated cellulose-degrading enzymes.[17]

Environmental conditions such as

soil profile.[23] Introduction of moisture exposes soil organic matter to enzyme catalysis[24] and also increases loss of soluble monomers via diffusion. Additionally, osmotic shock resulting from water potential changes can impact enzyme activities as microbes redirect energy from enzyme production to synthesizing osmolytes
to maintain cellular structures.

Extracellular enzyme activity in fungi during plant decomposition

Plant cell showing primary and secondary wall by CarolineDahl

Most of the extracellular enzymes involved in polymer degradation in leaf litter and soil have been ascribed to fungi.[25][26][27] By adapting their metabolism to the availability of varying amounts of carbon and nitrogen in the environment, fungi produce a mixture of oxidative and hydrolytic enzymes to efficiently break down lignocelluloses like wood. During plant litter degradation, cellulose and other labile substrates are degraded first[28] followed by lignin depolymerization with increased oxidative enzyme activity and shifts in microbial community composition.

In plant cell walls, cellulose and hemicellulose is embedded in a pectin scaffold

peroxidases and laccases. Many fungi have multiple genes encoding lignin-degrading exoenzymes.[31]

Most efficient wood degraders are

endoglucanases, cellobiohydrolase and β-glucosidase.[33] Production of endoglucanases is widely distributed among fungi and cellobiohydrolases have been isolated in multiple white-rot fungi and in plant pathogens.[33] β-glucosidases are secreted by many wood-rotting fungi, both white and brown rot fungi, mycorrhizal fungi[34] and in plant pathogens. In addition to cellulose, β-glucosidases can cleave xylose, mannose and galactose.[35]

In white-rot fungi such as

humic substances.[39]

Brown-rot basidiomycetes are most commonly found in coniferous forests, and are so named because they degrade wood to leave a brown residue that crumbles easily. Preferentially attacking hemicellulose in wood, followed by cellulose, these fungi leave lignin largely untouched.[40] The decayed wood of soft-rot Ascomycetes is brown and soft. One soft-rot Ascomycete, Trichoderma reesei, is used extensively in industrial applications as a source for cellulases and hemicellulases.[41] Laccase activity has been documented in T. reesei, in some species in the Aspergillus genus[42] and in freshwater ascomycetes.[43]

Measuring fungal extracellular enzyme activity in soil, plant litter, and other environmental samples

Electronic PH meter
Electronic PH meter

Methods for estimating soil enzyme activities involve sample harvesting prior to analysis, mixing of samples with buffers and the use of substrate. Results can be influenced by: sample transport from field-site, storage methods, pH conditions for assay, substrate concentrations, temperature at which the assay is run, sample mixing and preparation.[44]

For hydrolytic enzymes, colorimetric assays are required that use a

fluorometric assays that use a 4-methylumbelliferone (MUF)-linked substrate.[46]

Oxidative enzymes such as phenol oxidase and peroxidase mediate lignin degradation and humification.[47] Phenol oxidase activity is quantified by oxidation of L-3, 4-dihydoxyphenylalanine (L-DOPA), pyrogallol (1, 2, 3-trihydroxybenzene), or ABTS (2, 2’-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid). Peroxidase activity is measured by running the phenol oxidase assay concurrently with another assay with L-DOPA and hydrogen peroxide (H2O2) added to every sample.[48] The difference in measurements between the two assays is indicative of peroxidase activity. Enzyme assays typically apply proxies that reveal exo-acting activities of enzymes. Exo-acting enzymes hydrolyze substrates from the terminal position. While activity of endo-acting enzymes which break down polymers midchain need to be represented by other substrate proxies. New enzyme assays aim to capture the diversity of enzymes and assess the potential activity of them in a more clear way.[49][50][51]

With newer technologies available, molecular methods to quantify abundance of enzyme-coding genes are used to link enzymes with their producers in soil environments.

proteomic methods can reveal the presence of enzymes in the environment and link to the organisms producing them.[55]

Process Enzyme Substrate
Cellulose-degradation Cellobiohydrolase

β-glucosidase

pNP, MUF[33][56]
Hemicellulose-degradation β-glucosidases

Esterases

pNP, MUF[57][58]
Polysaccharide-degradation α-glucosidases

N-acetylglucosaminidase

pNP, MUF[59]
Lignin-degradation Mn-peroxidase

Laccase (polyphenol oxidase)

Peroxidase

Pyrogallol, L-DOPA, ABTS[38]

L-DOPA, ABTS[39]

Applications of fungal extracellular enzymes

Application Enzymes & their uses
Paper production Cellulases – improve paper quality and smooth fibers[60]

Laccases – soften paper and improving bleaching[61]

Biofuel generation Cellulases – for production of renewable liquid fuels[62]
Dairy industry Lactase – part of β-glucosidase family of enzymes and can break down lactose to glucose and galactose

Pectinases – in the manufacture of yogurt

Brewing industry
Black Sheep Brewery Tour
Black Sheep Brewery Tour
 Beer production and malting[63]
Fruit and jam manufacturing

Jelly Jars - Tanglewood Gardens - Nova Scotia, Canada

Pectinases, cellulases – to clarify fruit juices and form jams
Bioremediation Laccases – as biotransformers to remove nonionic
surfactants[64][65]
Waste water treatment Peroxidases - removal of pollutants by precipitation[66][67]
Sludge treatment Lipases - used in degradation of particulate organic matter[68]
Phytopathogen management Hydrolytic enzymes produced by fungi, e.g. Fusarium graminearum, pathogen on cereal grains resulting in economic losses in agriculture [69]
Resource management

Water retention

Soil aggregates and water infiltration influence enzyme activity[70][71]
Soil fertility and plant production Use of enzyme activity as indicator of soil quality[71][72]
Composting

Drums with septic tank sludge with different amounts of urea added (6881892839)

Impacts of composting municipal solid waste on soil microbial activity[10]
Soil organic matter stability Impact of temperature and soil respiration on enzymatic activity and its effect on soil fertility[73]
Climate change indicators

Impact on soil processes

Potential increase in enzymatic activity leading to elevated CO2 emissions[74]
Quantifying
global warming
outcomes		 Predictions based on soil organic matter decomposition[75] and strategies for mitigation[76]
Impact of elevated CO2 on enzyme activity & decomposition Understanding the implication of microbial responses and its impact on terrestrial ecosystem functioning[77]

See also

References

  1. ^
    S2CID 20188510
    .
  2. ^
    ISSN 0038-0717
    .
  3. S2CID 4384243
    .
  4. ISBN 978-1-55581-379-6
    .
  5. PMID 20189677
    .
  6. PMID 14638418
    .
  7. S2CID 4420494
    .
  8. S2CID 9213544
    .
  9. PMID 16213577
    .
  10. ^
    ISSN 0038-0717
    .
  11. PMID 18275861
    .
  12. ^
    ISSN 0038-0717
    .
  13. PMID 12473107
    .
  14. ISSN 0038-0717
    .
  15. ISSN 1613-3382
    .
  16. PMID 21776033
    .
  17. PMID 15182839
    .
  18. S2CID 97965526
    .
  19. ISSN 0038-0717
    .
  20. ISSN 0038-0717
    .
  21. S2CID 10919578
    .
  22. S2CID 2862965
    .
  23. S2CID 97005809
    .
  24. S2CID 2815843
    .
  25. PMID 16102603
    .
  26. ISSN 1543-592X
    .
  27. doi:10.17221/134/2009-PSE
    .
  28. ISSN 0378-1127
    .
  29. PMID 11423142
    .
  30. PMID 19497379
    .
  31. S2CID 23324645
    .
  32. PMID 16200498
    .
  33. ^
    PMID 18371173
    .
  34. S2CID 84906200
    .
  35. PMID 17159214
    .
  36. PMID 7887613
    .
  37. S2CID 23523898
    .
  38. ^
    ISSN 0141-0229
    .
  39. ^
    PMID 16472305
    .
  40. S2CID 96847091
    .
  41. S2CID 4830678
    .
  42. PMID 23270588
    .
  43. PMID 15632424
    .
  44. ISSN 0038-0717
    .
  45. ISSN 0046-5070
    .
  46. ISSN 0038-0717
    .
  47. ISSN 0038-0717
    .
  48. ISSN 0038-0717
    .
  49. S2CID 83660222
    .
  50. PMID 21329211
    .
  51. ISSN 0948-3055
    .
  52. S2CID 39272773
    .
  53. S2CID 15755901
    .
  54. S2CID 26713396
    .
  55. ISSN 0038-0717
    .
  56. PMID 12209002
    .
  57. PMID 15652973
    .
  58. ISSN 0022-5142
    .
  59. ISSN 1749-4613
    .
  60. S2CID 24813930
    .
  61. ISSN 0141-0229
    .
  62. PMID 19502046
    .
  63. ISBN 9781444309935. {{cite book}}: |journal= ignored (help
    )
  64. PMID 19429559
    .
  65. S2CID 96397441
    .
  66. ISSN 0926-3373
    .
  67. S2CID 1662318
    .
  68. PMID 12502058
    .
  69. S2CID 45168988
    .
  70. ISSN 0167-8809
    .
  71. ^
    ISSN 0306-9192
    .
  72. ISSN 0038-0717
    .
  73. ISSN 0280-6509
    .
  74. S2CID 86293310
    .
  75. S2CID 86672269
    .
  76. S2CID 153406514
    .
  77. ISSN 1754-5048
    .

Further reading

External links
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