Title: Evaluating models of cellulose degradation by Fibrobacter succinogenes S85

Abstract

Fibrobacter succinogenes S85 is an anaerobic non-cellulosome utilizing cellulolytic bacterium originally isolated from the cow rumen microbial community. Efforts to elucidate its cellulolytic machinery have resulted in the proposal of numerous models which involve a combination of cell-surface attachment via a combination of cellulose-binding fibro-slime proteins and pili, the production of cellulolytic vesicles, and the entry of cellulose fibers into the periplasmic space. Here, we used a combination of RNA-sequencing, proteomics, and transmission electron microscopy (TEM) to further elucidate the cellulolytic mechanism of F. succinogenes. Our RNA-sequence analysis shows that genes encoding Type II and III secretion systems, fibro-slime proteins, and pili are differentially expressed on cellulose, relative to glucose. A subcellular fractionation of cells grown on cellulose revealed that carbohydrate active enzymes associated with cellulose deconstruction and fibro-slime proteins were greater in the extracellular media, as compared to the periplasm and outer membrane fractions. TEMs of samples harvested at mid-exponential and stationary phases of growth on cellulose and glucose showed the presence of grooves in the cellulose between the bacterial cells and substrate, suggesting enzymes work extracellularly for cellulose degradation. Membrane vesicles were only observed in stationary phase cultures grown on cellulose. Furthermore, these results provide evidence that F.more » succinogenes attaches to cellulose fibers using fibro-slime and pili, produces cellulases, such as endoglucanases, that are secreted extracellularly using type II and III secretion systems, and degrades the cellulose into cellodextrins that are then imported back into the periplasm for further digestion by β-glucanases and other cellulases.« less

Authors:

Burnet, Meagan C. ^[1]; Dohnalkova, Alice C. ^[1]; Neumann, Anthony P. ^[2]; Lipton, Mary S. ^[1]; Smith, Richard D. ^[1]; Suen, Garret ^[2]; Callister, Stephen J. ^[1]

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+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Univ. of Wisconsin-Madison, Madison, WI (United States)

Publication Date:

Wed Dec 02 00:00:00 EST 2015

Research Org.:

Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1241081

Report Number(s):

PNNL-SA-111279
Journal ID: ISSN 1932-6203; 34708; 47418; 48680; KP1601010

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

PLoS ONE

Additional Journal Information:

Journal Volume: 10; Journal Issue: 12; Journal ID: ISSN 1932-6203

Publisher:

Public Library of Science

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; Environmental Molecular Sciences Laboratory; cellulose; outer membrane proteins; glucose; vesicles; periplasm; carbohydrates; cellulases; cell binding