Thermotolerant and mesophylic fungi from sugarcane bagasse and their prospection for biomass-degrading enzyme production

Abstract

Nineteen fungi and seven yeast strains were isolated from sugarcane bagasse piles from an alcohol plant located at Brazilian Cerrado and identified up to species level on the basis of the gene sequencing of 5.8S-ITS and 26S ribosomal DNA regions. Four species were identified: Kluyveromyces marxianus, Aspergillus niger, Aspergillus sydowii and Aspergillus fumigatus, and the isolates were screened for the production of key enzymes in the saccharification of lignocellulosic material. Among them, three strains were selected as good producers of hemicellulolitic enzymes: A. niger (SBCM3), A. sydowii (SBCM7) and A. fumigatus (SBC4). The best β-xylosidase producer was A. niger SBCM3 strain. This crude enzyme presented optimal activity at pH 3.5 and 55 °C (141 U/g). For β-glucosidase and xylanase the best producer was A. fumigatus SBC4 strain, whose enzymes presented maximum activity at 60 °C and pH 3.5 (54 U/g) and 4.0 (573 U/g), respectively. All these crude enzymes presented stability around pH 3.0–8.0 and up to 60 °C, which can be very useful in industrial processes that work at high temperatures and low pHs. These enzymes also exhibited moderate tolerance to ethanol and the sugars glucose and xylose. These similar characteristics among these fungal crude enzymes suggest that they can be used synergistically in cocktails in future studies of biomass conversion with potential application in several biotechnological sectors.

Synergistic action of an Aspergillus (hemi-)cellulolytic consortium on sugarcane bagasse saccharification

“…These fungal strains were obtained from the Microorganisms Collection of Laboratory of Environmental Microbiology, Federal University of Uberlândia (LAMIC-UFU), Brazil. They were previously isolated from SCB piles and identified at the specie level by sequencing the ribosomal DNA (Santos et al, 2015).…”

“…One unit of enzyme activity (U) was defined as the amount of enzyme required to release one μmol of p-nitrophenol per minute in the assay conditions. A standard curve of p-nitrophenol was built for quantification (Santos et al, 2015). All experiments were performed in triplicate.…”

“…The SSF plays a prominent role in the use of agroindustrial residues, since it allows the growth of microorganisms in these alternative substrates of lower cost, making possible the production of several microbial enzymes with an elevated yield and a lower cost in comparison to the most used culture media (Pereira et al, 2015;Rodrigues et al, 2017;Singhania et al, 2010). Aspergillus strains have been described in previous studies as good producers of extracellular enzymes, especially xylanases by SSF (Gomes et al, 2016;Santos et al, 2015). Moretti et al (2012) reported a maximum activity of xylanase by Aspergillus fumigatus M.7.1 strain of 1040.0 U g −1 in 144 h of fermentation, using SCB and WB as substrates.…”

“…On the other hand, the use of enzymes in the hydrolysis step has an elevated cost when it comes to the use of commercial cocktails. In order to solve this challenge, it is important to search for efficient and economically viable enzyme-producing microorganisms (Moretti et al, 2012;Santos et al, 2015). The hydrolytic enzymes are mainly produced by filamentous fungi and several studies have been performed to select strains with a high rate of enzyme production, especially hemicellulases and cellulases (Boonyuen et al, 2014;Santos et al, 2015).…”

“…In order to solve this challenge, it is important to search for efficient and economically viable enzyme-producing microorganisms (Moretti et al, 2012;Santos et al, 2015). The hydrolytic enzymes are mainly produced by filamentous fungi and several studies have been performed to select strains with a high rate of enzyme production, especially hemicellulases and cellulases (Boonyuen et al, 2014;Santos et al, 2015). Among the cellulases, β-glucosidases or cellobiases (EC 3.2.1.21) have the function of ending the hydrolysis of cellulose, releasing glucose from cellobioses and cellooligosaccharides previously generated by the action of other enzymes of the cellulolytic complex, which are fundamental for the success of the saccharification process (Murphy et al, 2013;Watanabe and Tokuda, 2010).…”