Biofuels are an attractive means to prevent a further increase of carbon dioxide emissions. Currently, gasoline is blended with ethanol at various percentages. However, butanol has several advantages over ethanol, such as higher energy content, lower water absorption, better blending ability, and use in conventional combustion engines without modification. Like ethanol, it can be produced fermentatively or petrochemically. Current crude oil prices render the biotechnological process economic again. The best-studied bacterium to perform a butanol fermentation is Clostridium acetobutylicum. Its genome has been sequenced, and the regulation of solvent formation is under intensive investigation. This opens the possibility to engineer recombinant strains with superior biobutanol-producing ability.

Biobutanol: An attractive biofuel

The solvent-forming clostridia have attracted interest because of their ability to convert a range of carbohydrates to end-products such as acetone, butanol and ethanol. Polymeric substrates such as cellulose, hemicellulose and starch are degraded by extracellular enzymes. The majority of cellulolytic clostridia, typified by Clostridium thermocellum, produce a multi-enzyme cellulase complex in which the organization of components is critical for activity against the crystalline substrate. A variety of enzymes involved in degradation of hemicellulose and starch have been identified in different strains. The products of degradation, and other soluble substrates, are accumulated via membrane-bound transport systems which are generally poorly characterized. It is clear, however, that the phosphoenolpyruvate-dependent phosphotransferase system (PTS) plays a major role in solute uptake in several species. Accumulated substrates are converted by intracellular enzymes to end-products characteristic of the organism, with production of ATP to support growth. The metabolic pathways have been described, but understanding of mechanisms of regulation of metabolism is incomplete. Synthesis of extracellular enzymes and membrane-bound transport systems is commonly subject to catabolite repression in the presence of a readily metabolized source of carbon and energy. While many genes encoding cellulases, xylanases and amylases have been cloned and sequenced, little is known of control of their expression. Although the mechanism of catabolite repression in clostridia is not understood, some recent findings implicate a role for the PTS as in other low G-C Gram-positive bacteria. Emphasis has been placed on describing the mechanisms underlying the switch of C. acetobutylicum fermentations from acidogenic to solventogenic metabolism at the end of the growth phase. Factors involved include a lowered pH and accumulation of undissociated butyric acid, intracellular concentration of ATP and reduced pyridine nucleotides, nutrient limitation, and the interplay between pathways of carbon and electron flow. Genes encoding enzymes of solvent pathways have been cloned and sequenced, and their expression correlated with the pattern of end-product formation in fermentations. There is evidence that the initiation of solvent formation may be subject to control mechanisms similar to other stationary-phase phenomena, including sporulation. The application of recently developed techniques for genetic manipulation of the bacterium is improving understanding of the regulatory circuits, but a complete molecular description of the control of solvent formation remains elusive. Experimental manipulation of the pathways of electron flow in other species has been shown to influence the range and yield of fermentation end-products. Acid-forming clostridia can, under appropriate conditions, be induced to form atypical solvents as products. While the mechanisms of regulation of gene expression are not at all understood, the capacity to adapt in this way further illustrates the metabolic flexibility of clostridial strains.

Physiology of Carbohydrate to Solvent Conversion by Clostridia

Two endoxylanases produced by C. acetobutylicum ATCC 824 were purified to homogeneity by column chromatography. Xylanase A, which has a molecular weight of 65,000, hydrolyzed larchwood xylan randomly, yielding xylohexaose, xylopentaose, xylotetraose, xylotriose, and xylobiose as end products. Xylanase B, which has a molecular weight of 29,000, also hydrolyzed xylan randomly, giving xylotriose and xylobiose as end products. Xylanase A hydrolyzed carboxymethyl cellulose with a higher specific activity than xylan. It also exhibited high activity on acid-swollen cellulose. Xylanase B showed practically no activity against either cellulose or carboxymethyl cellulose but was able to hydrolyze lichenan with a specific activity similar to that for xylan. Both xylanases had no aryl-β-xylosidase activity. The smallest oligosaccharides degraded by xylanases A and B were xylohexaose and xylotetraose, respectively. The two xylanases demonstrated similar Km and Vmax values but had different pH optima and isoelectric points. Ouchterlony immunodiffusion tests showed that xylanases A and B lacked antigenic similarity.

Purification and Characterization of Two Endoxylanases from Clostridium acetobutylicum ATCC 824

An α-L-arabinofuranosidase (EC 3.2.1.55) has been purified from the extracellular culture fluid of Clostridium acetobutylicum ATCC 824 and characterized. The enzyme was a single polypeptide with a molecular weight of 94 000, an isoelectric point of 8.15, and a pH optimum between pH 5.0 and 5.5. The Km and Vmax values for p-nitrophenyl-α-L-arabinofuranoside were 4.0 mM and 36.4 μmol∙min−1·mg protein−1, respectively. The enzyme had practically no activity against other p-nitrophenylglycosides with the exception of p-nitrophenyl-α-D-glucoside which it hydrolysed at 9% of the rate exhibited on p-nitrophenyl-α-L-arabinofuranoside. It degraded arabinan in an exo-manner, but exhibited no activity on carboxymethylcellulose, arabinogalactan, arabinoxylan, or oat spelt xylan. However, when it was incubated with the purified xylanase B, also obtained from C. acetobutylicum, it acted cooperatively to increase the rate of hydrolysis of oat spelt xylan. Arabinose was detected as one of the hydrolysis products.

Purification and characterization of an α-L-arabinofuranosidase from Clostridium acetobutylicum ATCC 824

Organic Acid and Solvent Production

Fermentation of xylan by Clostridium acetobutylicum

Popular Tasks used by Researchers

How can I help with your research?

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

We encountered an error while loading the panel. Please try refreshing the page.

Something went wrong

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

Anyone with the link can view this chat. You can switch it back to private anytime.

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

S.A. Lemmel

Author Tools

Chat about Author

Papers

Fermentation of xylan by Clostridium acetobutylicum