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

• Published in: Journal of applied microbiology Vol. 111; no. 5; pp. 1086 - 1096
• Main Authors: Bootten, T.J, Joblin, K.N, McArdle, B.H, Harris, P.J
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-11-2011; Blackwell
• Subjects: alfalfa; Animals; biofuels; Biological and medical sciences; Caecomyces; Cattle; Cell Wall - metabolism; Cell Wall - microbiology; cell walls; cellulose; Cellulose - metabolism; coculture; Coculture Techniques; degradation; forage; Fundamental and applied biological sciences. Psychology; fungi; Goats; hay; lignified cell wall; lignin; Lignin - metabolism; lignocellulose; Medicago sativa; Medicago sativa - metabolism; Medicago sativa - microbiology; Methane - metabolism; Methanobrevibacter - growth & development; Methanobrevibacter smithii; methanogens; Microbiology; Microscopy, Electron, Scanning; Neocallimastigales - growth & development; Neocallimastigales - isolation & purification; Neocallimastigales - metabolism; Neocallimastix; Neocallimastix frontalis; Pectins - metabolism; Piromyces; Rumen - microbiology; rumen bacteria; rumen fungi; ruminants; scanning electron microscopy; secondary xylem; Sheep; stems; weight loss; xylan; Xylans - metabolism; Xylem - metabolism; Xylem - microbiology; Xylem - ultrastructure; Applied microbiology; Medicago sativa; Rumen; Piromyces; lignified cell wall; rumen fungi; Cell wall; Neocallimastigomycota; Degradation; Fungi; Leguminosae; Dicotyledones; Angiospermae; Methanogenesis; Spermatophyta; Caecomyces; Lucerne; Culture; Neocallimastix
• ISSN: 1364-5072; 1365-2672
• DOI: 10.1111/j.1365-2672.2011.05127.x

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.