Degradation of lignified secondary cell walls of lucerne (Medicago sativa L.) by rumen fungi growing in methanogenic co-culture

Abstract

Aims: To compare the abilities of the monocentric rumen fungi Neocallimastix frontalis, Piromyces communis and Caecomyces communis, growing in coculture with Methanobrevibacter smithii, to colonize and degrade lignified secondary cell walls of lucerne (alfalfa) hay. Methods and Results: The cell walls of xylem cylinders isolated from stems of lucerne contained mostly xylans, cellulose and lignin together with a small proportion of pectic polysaccharides. All of these major components were removed during incubation with the three fungi, and differing cell wall polysaccharides were degraded to different extents. The greatest dry weight loss was found with N. frontalis and least with C. communis, and scanning electron microscopy revealed that these extensively colonized different cell types. C. communis specifically colonized secondary xylem fibres and showed much less degradation than N. frontalis and P. communis. Conclusions: Neocallimastix frontalis and P. communis were efficient degraders of the cell walls of lucerne xylem cylinders. Degradation occurred of pectic polysaccharides, xylan and cellulose. Loss of lignin from the xylem cylinders probably resulted from the cleavage of xylan releasing xylan–lignin complexes. Significance and Impact of the Study: Unlike rumen bacteria, the rumen fungi N. frontalis, P. communis and C. communis are able to degrade lignified secondary walls in lucerne stems. These fungi could improve forage utilization by ruminants and may have potential in the degradation of lignocellulosic biomass in the production of biofuels.

Live yeasts enhance fibre degradation in the cow rumen through an increase in plant substrate colonization by fibrolytic bacteria and fungi

“…We found that fungi were mostly abundant on forage samples (WS, AH), in agreement with other authors who reported high abundances in sheep fed high forage-based diets (Fonty and Grenet 1994;Denman and McSweeney 2006). Rumen fungi colonize preferentially lignocellulosic tissues, and break down polysaccharide-lignin linkages thanks both to the secretion of active esterases, but also to physical disruption of fibre because of the extension of a complex rhizoidal network (Fonty et al 1999;Bootten et al 2011).…”

Application of Transcriptomics to Compare the Carbohydrate Active Enzymes That Are Expressed by Diverse Genera of Anaerobic Fungi to Degrade Plant Cell Wall Carbohydrates

“…Differences in the relative proportions of CAZyme transcripts predicted to be involved in cellulose, hemicellulose, and pectin saccharification could help decrease direct competition for finite resources in the rumen and facilitate the co-existence of multiple genera of anaerobic fungi in the gut. A study by Bootten et al ( 2011 ) found that different genera of anaerobic fungi were able to colonize and degrade lignified secondary plant cell walls with differing efficiency and specificity. N. frontalis and P. communis were highly efficient at degrading all plant cell wall structures whereas Caecomyces communis preferentially degraded xylem tissues and was much less efficient than the other two genera studied (Bootten et al, 2011 ).…”

Simultaneous Amplicon Sequencing to Explore Co-Occurrence Patterns of Bacterial, Archaeal and Eukaryotic Microorganisms in Rumen Microbial Communities

“…Protozoa and fungi, although far less abundant than the bacteria and archaea in terms of cell numbers, can make up approximately half of the total rumen microbial biomass [15]. Until recently, species identification and physiological characteristics of fungal and ciliate communities colonising the gastrointestinal tracts of herbivores have typically been assessed by using microscopy [16],[17] and cultivation-based techniques [18],[19]. Liggenstoffer et al .…”