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Title: The diversity and specificity of the extracellular proteome in the cellulolytic bacterium Caldicellulosiruptor bescii is driven by the nature of the cellulosic growth substrate

Background: Caldicellulosiruptor bescii is a thermophilic cellulolytic bacterium that efficiently deconstructs lignocellulosic biomass into sugars, which subsequently can be fermented into alcohols, such as ethanol, and other products. Deconstruction of complex substrates by C. bescii involves a myriad of highly abundant, substrate-specific extracellular solute binding proteins (ESBPs) and carbohydrate-active enzymes (CAZymes) containing carbohydrate-binding modules (CBMs). Mass spectrometry-based proteomics was employed to investigate how these substrate recognition proteins and enzymes vary as a function of lignocellulosic substrates.Results:Proteomic analysis revealed several key extracellular proteins that respond specifically to either C5 or C6 mono- and polysaccharides. These include proteins of unknown functions (PUFs), ESBPs, and CAZymes. ESBPs that were previously shown to interact more efficiently with hemicellulose and pectin were detected in high abundance during growth on complex C5 substrates, such as switchgrass and xylan. Some proteins, such as Athe_0614 and Athe_2368, whose functions are not well defined were predicted to be involved in xylan utilization and ABC transport and were significantly more abundant in complex and C5 substrates, respectively. The proteins encoded by the entire glucan degradation locus (GDL; Athe_1857, 1859, 1860, 1865, 1867, and 1866) were highly abundant under all growth conditions, particularly when C. bescii was grown on cellobiose, switchgrass,more » or xylan. In contrast, the glycoside hydrolases Athe_0609 (Pullulanase) and 0610, which both possess CBM20 and a starch binding domain, appear preferential to C5/complex substrate deconstruction. Some PUFs, such as Athe_2463 and 2464, were detected as highly abundant when grown on C5 substrates (xylan and xylose), also suggesting C5-substrate specificity. In conclusion, this study reveals the protein membership of the C. bescii secretome and demonstrates its plasticity based on the complexity (mono-/disaccharides vs. polysaccharides) and type of carbon (C5 vs. C6) available to the microorganism. The presence or increased abundance of extracellular proteins as a response to specific substrates helps to further elucidate C. bescii’s utilization and conversion of lignocellulosic biomass to biofuel and other valuable products. This includes improved characterization of extracellular proteins that lack discrete functional roles and are poorly/not annotated.« less
Authors:
 [1] ; ORCiD logo [2] ;  [3] ; ORCiD logo [4] ;  [5] ;  [6] ;  [7] ; ORCiD logo [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC); Univ. of Tennessee, Knoxville, TN (United States). Dept. of Genome Science and Technology
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC)
  3. Univ. of Georgia, Athens, GA (United States). Dept. of Biochemistry and Molecular Biology; Johann Wolfgang Goethe Univ., Frankfurt Am Main (Germany). Inst. of Molecular Biosciences, Dept. of Molecular Microbiology and Bioenergetics
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC); Univ. of Arkansas for Medical Sciences, Little Rock, AR (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC); Univ. of Georgia, Athens, GA (United States). Dept. of Biochemistry and Molecular Biology
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC); North Carolina State Univ., Raleigh, NC (United States). Dept. of Chemical and Biomolecular Engineering
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC); Univ. of Georgia, Athens, GA (United States). Dept. of Biochemistry and Molecular Biology
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Biotechnology for Biofuels
Additional Journal Information:
Journal Volume: 11; Journal Issue: 1; Journal ID: ISSN 1754-6834
Publisher:
BioMed Central
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES
OSTI Identifier:
1435256