Endophytic Fungi as Pretreatment to Enhance Enzymatic Hydrolysis of Olive Tree Pruning

Abstract

Olive tree pruning, as one of the most abundant lignocellulosic residues in Mediterranean countries, has been evaluated as a source of sugars for fuel and chemicals production. A mild acid pretreatment has been combined with a fungal pretreatment using either two endophytes (Ulocladium sp. and Hormonema sp.) or a saprophyte (Trametes sp. I-62). The use of endophytes is based on the important role that some of them play during the initial stages of wood decomposition. Without acid treatment, fungal pretreatment with Ulocladium sp. provided a nonsignificant enhancement of 4.6% in glucose digestibility, compared to control. When a mild acid hydrolysis was carried out after fungal pretreatments, significant increases in glucose digestibility from 4.9% to 12.0% (compared to control without fungi) were observed for all fungal pretreatments, with maximum values yielded by Hormonema sp. However, despite the observed digestibility boost, the total sugar yields (taking into account solid yield) were not significantly increased by the pretreatments. Nevertheless, based on these preliminary improvements in digestibility, this work proves the potential of endophytic fungi to boost the production of sugar from olive tree pruning, which would add an extra value to the bioeconomy of olive crops.

Fungal Hydrolysis of Food Waste: Review of Used Substrates, Conditions, and Microorganisms

“…Further research is needed to identify more strategies, with different substrates and optimizing cultivation conditions. This would help to valorize different types of food waste and make fungal hydrolysis more efficient in a scale up process [38]. For example, one of the research directions can be fungal strain optimization and creation of mutants with enhanced enzyme-producing capabilities, which would in turn increase the efficiency of substrate hydrolyzation.…”

“…When using fungi for substrate degradation, it can be referred as fungal hydrolysis. For some food wastes that are complex in their structure, this first stage has a great importance to enhance the enzymatic depolymerization of biomass into sugars that can be later fermented into high value products [38]. For fungal hydrolysis the most important parameters are temperature, medium pH level and inoculum size [39].…”

Enzymatic Hydrolysis of Two-way Pretreated Sawdust of <i>Eucalyptus globulus</i> and <i>Cupressus lusitanica</i>

“…The next highest lignin loss (14.51%) was obtained during pretreatment of the sawdust by NaOH-P. squarrosa 003-2G for 60 days. Unlike the endophytic fungi where degradation of lignin components within 28 days, the saprophytes take longer time in degradation of the lignin content on E. globulus (Martín-Sampedro et al, 2017). Relatively low lignin loss of 11.73% was seen during C. lusitanica pretreatment with NaOH-P. squarrosa 003-2G (Figure 2) which is lower than the loss of E. globulus.…”

“…Combination of wood rot fungal pretreatment with other pretreatment methods has been reported to increase enzymatic hydrolysis yield (Alexandropoulou et al, 2017;Martín-Sampedro et al, 2017). A mild alkali pretreatment of corn stalks with I. lacteus for 15 days significantly facilitated lignin degradation by wood rot fungi (Yu et al, 2009).…”

Nanomechanics of Lignin–Cellulase Interactions in Aqueous Solutions

“…In the past decades, some indirect methods (such as zeta potential measurement and simulated enzyme adsorption ,− ) have been developed to explore the lignin–cellulase interaction mechanism. It is speculated that the nonproductive adsorption of lignin to cellulase is mainly ascribed to a combined effect of multiple forces including hydrophobic, electrostatic, and hydrogen-bonding interactions. − Specifically, the hydrophobic groups of lignin and hydrophobic amino acid residues of cellulase might form the hydrophobic interaction, which has been considered as the main driving interaction for the nonproductive adsorption of lignin to cellulase. , The negatively charged groups (carboxyl and phenolic hydroxyl groups) of lignin and the positively charged groups (numerous amine groups) of cellulase could induce electrostatic interactions .…”