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Fungi isolated from Miscanthus and sugarcane: biomass conversion, fungal enzymes, and hydrolysis of plant cell wall polymers.

Shrestha P, Ibáñez AB, Bauer S, Glassman SI, Szaro TM, Bruns TD, Taylor JW - Biotechnol Biofuels (2015)

Bottom Line: To make a meaningful reduction in fossil fuel use, bioethanol must be produced from the entire plant rather than only its starch or sugars.Previously, we have reported on the isolation of 106 fungi from decaying leaves of Miscanthus and sugarcane (Appl Environ Microbiol 77:5490-504, 2011).We extend our analysis to assess not only their ability over an 8-week period to bioconvert Miscanthus cell walls but also their ability to secrete total protein, to secrete enzymes with the activities of xylanases, exocellulases, endocellulases, and beta-glucosidases, and to remove specific parts of Miscanthus cell walls, that is, glucan, xylan, arabinan, and lignin.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102 USA.

ABSTRACT

Background: Biofuel use is one of many means of addressing global change caused by anthropogenic release of fossil fuel carbon dioxide into Earth's atmosphere. To make a meaningful reduction in fossil fuel use, bioethanol must be produced from the entire plant rather than only its starch or sugars. Enzymes produced by fungi constitute a significant percentage of the cost of bioethanol production from non-starch (i.e., lignocellulosic) components of energy crops and agricultural residues. We, and others, have reasoned that fungi that naturally deconstruct plant walls may provide the best enzymes for bioconversion of energy crops.

Results: Previously, we have reported on the isolation of 106 fungi from decaying leaves of Miscanthus and sugarcane (Appl Environ Microbiol 77:5490-504, 2011). Here, we thoroughly analyze 30 of these fungi including those most often found on decaying leaves and stems of these plants, as well as four fungi chosen because they are well-studied for their plant cell wall deconstructing enzymes, for wood decay, or for genetic regulation of plant cell wall deconstruction. We extend our analysis to assess not only their ability over an 8-week period to bioconvert Miscanthus cell walls but also their ability to secrete total protein, to secrete enzymes with the activities of xylanases, exocellulases, endocellulases, and beta-glucosidases, and to remove specific parts of Miscanthus cell walls, that is, glucan, xylan, arabinan, and lignin.

Conclusion: This study of fungi that bioconvert energy crops is significant because 30 fungi were studied, because the fungi were isolated from decaying energy grasses, because enzyme activity and removal of plant cell wall components were recorded in addition to biomass conversion, and because the study period was 2 months. Each of these factors make our study the most thorough to date, and we discovered fungi that are significantly superior on all counts to the most widely used, industrial bioconversion fungus, Trichoderma reesei. Many of the best fungi that we found are in taxonomic groups that have not been exploited for industrial bioconversion and the cultures are available from the Centraalbureau voor Schimmelcultures in Utrecht, Netherlands, for all to use.

No MeSH data available.


Related in: MedlinePlus

Heat map(green = low, yellow = intermediate, red = high)of assessment of extracellular protein secreted by the fungi during 8 weeks of solid substrate cultures onMiscanthus. GenBank accession numbers are given for fungi isolated by us from Miscanthus or sugarcane. Protein concentrations were determined using the Bradford method with bovine serum albumin as the standard.
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Fig3: Heat map(green = low, yellow = intermediate, red = high)of assessment of extracellular protein secreted by the fungi during 8 weeks of solid substrate cultures onMiscanthus. GenBank accession numbers are given for fungi isolated by us from Miscanthus or sugarcane. Protein concentrations were determined using the Bradford method with bovine serum albumin as the standard.

Mentions: Endocellulase activity showed a different pattern than exocellulase activity in that it did not peak early and then decline. Instead, most fungi with strong endocellulase activity displayed high activities at weeks 2 through 8 with the highest activities coming at weeks 4 and 8. Fungal species that had better exocellulase activities typically also had higher endocellulase activities, with the notable exception of Sporothrix aff. lignivora, which showed the highest levels of endocellulase activity seen for any of the fungi, 384 μM glucose/min/mg protein at week 8; interestingly, S. aff. lignivora lacked exocellulase and xylanase activities. Both of these anomalies are likely a consequence of the low amount of protein secreted by this animal-associated fungus (Figure 3). E. aff. nigrum again showed consistently strong activity for weeks 2, 4, and 8, and two other Dothideomycetes also achieved high levels of activity, A. aff. tenuissima and Dothideomycete sp. For Sordariomycetes, in addition to the aforementioned S. aff. lignivora, A. aff. phaeospermum, C. aff. gramineum, and H. aff. koningii all showed high levels of endocellulase activity over extended periods, although H. aff. koningii was unusual in having the strongest activity at week 1, 234 μM glucose/min/mg protein. Moderate to low levels of endocellulase activity were manifested by cultures of positive control species: P. chrysosporium, P. placenta, N. crassa, and T. reesei QM9414, along with Chloridium sp1 and most species of Hypocreaceae, home to Trichoderma, Gibberella, and Fusarium spp., but not the aforementioned and very active, H. aff. koningii.


Fungi isolated from Miscanthus and sugarcane: biomass conversion, fungal enzymes, and hydrolysis of plant cell wall polymers.

Shrestha P, Ibáñez AB, Bauer S, Glassman SI, Szaro TM, Bruns TD, Taylor JW - Biotechnol Biofuels (2015)

Heat map(green = low, yellow = intermediate, red = high)of assessment of extracellular protein secreted by the fungi during 8 weeks of solid substrate cultures onMiscanthus. GenBank accession numbers are given for fungi isolated by us from Miscanthus or sugarcane. Protein concentrations were determined using the Bradford method with bovine serum albumin as the standard.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4362644&req=5

Fig3: Heat map(green = low, yellow = intermediate, red = high)of assessment of extracellular protein secreted by the fungi during 8 weeks of solid substrate cultures onMiscanthus. GenBank accession numbers are given for fungi isolated by us from Miscanthus or sugarcane. Protein concentrations were determined using the Bradford method with bovine serum albumin as the standard.
Mentions: Endocellulase activity showed a different pattern than exocellulase activity in that it did not peak early and then decline. Instead, most fungi with strong endocellulase activity displayed high activities at weeks 2 through 8 with the highest activities coming at weeks 4 and 8. Fungal species that had better exocellulase activities typically also had higher endocellulase activities, with the notable exception of Sporothrix aff. lignivora, which showed the highest levels of endocellulase activity seen for any of the fungi, 384 μM glucose/min/mg protein at week 8; interestingly, S. aff. lignivora lacked exocellulase and xylanase activities. Both of these anomalies are likely a consequence of the low amount of protein secreted by this animal-associated fungus (Figure 3). E. aff. nigrum again showed consistently strong activity for weeks 2, 4, and 8, and two other Dothideomycetes also achieved high levels of activity, A. aff. tenuissima and Dothideomycete sp. For Sordariomycetes, in addition to the aforementioned S. aff. lignivora, A. aff. phaeospermum, C. aff. gramineum, and H. aff. koningii all showed high levels of endocellulase activity over extended periods, although H. aff. koningii was unusual in having the strongest activity at week 1, 234 μM glucose/min/mg protein. Moderate to low levels of endocellulase activity were manifested by cultures of positive control species: P. chrysosporium, P. placenta, N. crassa, and T. reesei QM9414, along with Chloridium sp1 and most species of Hypocreaceae, home to Trichoderma, Gibberella, and Fusarium spp., but not the aforementioned and very active, H. aff. koningii.

Bottom Line: To make a meaningful reduction in fossil fuel use, bioethanol must be produced from the entire plant rather than only its starch or sugars.Previously, we have reported on the isolation of 106 fungi from decaying leaves of Miscanthus and sugarcane (Appl Environ Microbiol 77:5490-504, 2011).We extend our analysis to assess not only their ability over an 8-week period to bioconvert Miscanthus cell walls but also their ability to secrete total protein, to secrete enzymes with the activities of xylanases, exocellulases, endocellulases, and beta-glucosidases, and to remove specific parts of Miscanthus cell walls, that is, glucan, xylan, arabinan, and lignin.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102 USA.

ABSTRACT

Background: Biofuel use is one of many means of addressing global change caused by anthropogenic release of fossil fuel carbon dioxide into Earth's atmosphere. To make a meaningful reduction in fossil fuel use, bioethanol must be produced from the entire plant rather than only its starch or sugars. Enzymes produced by fungi constitute a significant percentage of the cost of bioethanol production from non-starch (i.e., lignocellulosic) components of energy crops and agricultural residues. We, and others, have reasoned that fungi that naturally deconstruct plant walls may provide the best enzymes for bioconversion of energy crops.

Results: Previously, we have reported on the isolation of 106 fungi from decaying leaves of Miscanthus and sugarcane (Appl Environ Microbiol 77:5490-504, 2011). Here, we thoroughly analyze 30 of these fungi including those most often found on decaying leaves and stems of these plants, as well as four fungi chosen because they are well-studied for their plant cell wall deconstructing enzymes, for wood decay, or for genetic regulation of plant cell wall deconstruction. We extend our analysis to assess not only their ability over an 8-week period to bioconvert Miscanthus cell walls but also their ability to secrete total protein, to secrete enzymes with the activities of xylanases, exocellulases, endocellulases, and beta-glucosidases, and to remove specific parts of Miscanthus cell walls, that is, glucan, xylan, arabinan, and lignin.

Conclusion: This study of fungi that bioconvert energy crops is significant because 30 fungi were studied, because the fungi were isolated from decaying energy grasses, because enzyme activity and removal of plant cell wall components were recorded in addition to biomass conversion, and because the study period was 2 months. Each of these factors make our study the most thorough to date, and we discovered fungi that are significantly superior on all counts to the most widely used, industrial bioconversion fungus, Trichoderma reesei. Many of the best fungi that we found are in taxonomic groups that have not been exploited for industrial bioconversion and the cultures are available from the Centraalbureau voor Schimmelcultures in Utrecht, Netherlands, for all to use.

No MeSH data available.


Related in: MedlinePlus