Fermentation of cellulose and production of cellulolytic and xylanolytic enzymes by anaerobic fungi from ruminant and non-ruminant herbivores

Abstract

Four anaerobic fungi were grown on filter paper cellulose and monitored over a 7-8 days period for substrate utilisation, fermentation products, and secretion of cellulolytic and xylanolytic enzymes. Two of the fungi (N1 and N2) were Neocallimastix species isolated from a ruminant (sheep) and the other two fungi were Piromyces species (E2 and R1) isolated from an Indian Elephant and an Indian Rhinoceros, respectively. The tested anaerobic fungi degraded the filter paper cellulose almost completely and estimated cellulose digestion rates were 0.25, 0.13, 0.21 and 0.18 g.l-1.h-1 for strains E2, N1, N2, R1, respectively. All strains secreted cellulolytic and xylanolytic enzymes, including endoglucanase, exoglucanase, beta-glucosidase and xylanase. Strain E2 secreted the highest levels of enzymes in a relatively short time. The product formation on avicel by enzymes secreted by the four fungi was studied. Both in the presence and absence of glucurono-1,5-delta-lactone, a specific inhibitor of beta-glucosidase, mainly glucose was formed but no cellobiose. Therefore the exoglucanase secreted by the four fungi is probably a glucohydrolase.

Fungi open new possibilities for anaerobic fermentation of organic residues

“…Compared to the mesophilic process, thermophilic dry fermentation proved to lead to higher methane yields and VS degradation when applied to cow dung [49] and to fibre-rich green yard waste (M Zak, personal communication). In fact, cellulase and xylanase activities in anaerobic fungal cultures had their optima at 50°C [12], which supports the importance of fungi in the anaerobic degradation of material rich in lignocelluloses.…”

“…More specific estimates on their role in the biogas reactor (BP1) were not possible however. Although the applied detection methods in the current study could not provide any information regarding fungal enzymatic activity, there is increasing evidence supporting the importance of facultative anaerobic fungi in producing enzymes for degradation of fibre-rich substrates [9,12,34]. Enzyme essays showed especially high cellulase, carboxymethylcellulase, xylanase and avicelase activities [9,10].…”

“…Teunissen et al [12] reported the highest production of acetate and formate, together with hydrogen, by the investigated strains of Neocallimastix and Piromyces. Furthermore, anaerobic fungi are building syntrophic interactions with archaea where the latter utilizes the fungiproduced hydrogen for methanogenesis [10], thus keeping the hydrogen partial pressure low -a prerequisite for a stable biogas process.…”

“…Fungi from anaerobic environments (e.g. Piromyces, Neocallimastix [12], Orpinomyces, Anaeromyces [10]) are possessing fibrolytic activity and are able to enhance the digestibility of fibrous feeds as was documented for cattle [34], as well as wild-living herbivores like buffalo [35] and elephants [9]. Celluloses and hemicelluloses are forming plant cell walls, and their penetration and disintegration are the limiting steps in the anaerobic digestion of fibrous material, especially if they are embedded within the lignocellulose complex [36].…”

“…The presence of episymbiotic methanogens in ruminal ciliated protozoa was already proven in the early 1980s [11]. Ten years later, Teunissen et al [12] found that the most abundant fermentation products of fungi in the anaerobic process are acetate, formate and hydrogen. Furthermore, anaerobic fungi are known to form co-cultures with ruminal methanogenic archaea which utilize the fungal hydrogen production [13].…”