Clostridium acetobutylicum

From MicrobeWiki, the student-edited microbiology resource

A Microbial Biorealm page on the genus Clostridium acetobutylicum

Image of Clostridium acetobutylicum courtesy of NCBI.

Classification

Higher order taxa

Bacteria (Domain); Firmicutes (Phylum); Clostridia (Class); Clostridiales (Order); Clostridiaceae (Family); Clostridium (Genus)

Species

Clostridium acetobutylicum

Clostridium acetobutylicum ATCC 824 is considered the type strain.

NCBI: Taxonomy

Description and significance

Clostridium acetobutylicum is a Gram positive bacillus. C. acetobutylicum is a soil dwelling and mesophilic with optimal temperatures of 10-65C.It is anaerobic and saccharolytic capable of producing a number of different commercially useful products; most notably acetone, ethanol and butanol.

It was first isolated between 1912 and 1914. Chaim Weizmann cultured the bacteria to be used to produce acetone, ethanol and butanol (ABE method) which was used to produce TNT and gunpowder in the first World War. Following WWI, the ABE process was widely used until the 1950's when petrochemical processes were more cost-effective due to the cost and availability of petroleum fuel sources.

The recent fossil fuel crisis has spurred more research into C. acetobutylicum and the utilization of the ABE process.



Describe the appearance, habitat, etc. of the organism, and why it is important enough to have its genome sequenced. Describe how and where it was isolated. Include a picture or two (with sources) if you can find them.

Genome structure

The genome of Clostridium acetobutylicum ATCC 824 has been sequenced. This is the model strain for solvent-producing bacteria. It consists of one circular chromosome with 3,940,880 bp. The chromosome contains 11 operons coding for ribosomes, each of which is near the oriC and oriented in the direction of the leading strand of the replication fork. This is a characteristic commonly observed known as gene dosage, in which highly transcribed genes are placed near the oriC. There is little strand bias with approximately 51.5% of genes being transcribed from forward strand and 49.5% from the complementary strand.

In addition, the genome consists of one megaplasmid involved with solvent production and aptly named pSOL1. pSOL1 contains 192,000 bp and codes for 178 polypeptides. Examination of the plasmid indicates no obvious bias in the coding strand. pSOL1 contains four genes which are vital for alcohol and acetone production and the loss of this plasmid contributes to degeneration of the strain after many vegetative transfers or being maintained in a continuous culture. Further, mutants lacking these genes and unable to produce solvent resume acetone and alcohol production upon complementation of the genes via plasmids.

Examination of other strains of the organism such as ATCC 4259 have demonstrated that solvent producing genes again exist on the plasmid, named pWEIZ. Degeneration of the strain due to serial culturing is likely due to loss of this plasmid. Interestingly, these degenerate strains also do not sporulate spurring the idea that genes involved in sporulation also exist on the plasmid.


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Cell structure and metabolism

Overview of metabolism courtesy of Jörk Nölling.

The pathways which produce solvents are those most notable in C. acetobutylicum. Acetone, acetate, butanol, butyrate, and ethanol are all made from acetyl-CoA.

Mutants which do not produce acetone or alcohol, such as mutant M5 of strain C. acetobutylicum ATCC 824 have been shown to lack of three enzymes in vitro: butyraldehyde dehydrogenase (BYDH), acetoacetate decarboxylase(AADC), and acetoacetyl-coenzyme A:acetate/butyrate:coenzyme A-transferase (CoAT). These enzymes are coded for on the plasmid within the sol operon by the following genes: AADC (adc), CoAT (ctfA, ctfB) and BYDH (aad).

In addition, C. acetobutylicum codes for many proteins that aid in the breakdown of xylan, levan, pectin, starch, and other polysaccharides. Interestingly, while the presence of genes which commonly code for cellusomes, protein complexes which breakdown crystalline cellulose, has been detected, the organism is unable to grow solely on cellulose substrates.

Nitrogen fixation operon is conserved see article 1.

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Ecology

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Pathology

C. acetobutylicum is completely benign, however, many other species in the Clostridium genus are known pathogens, including: Clostridium difficile, Clostridium botulinum, Clostridium tetani, and Clostridium perfringen.


How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

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References

Taxonomy:NCBI

Nolling J et al., "Genome sequence and comparative analysis of the solvent-producing bacterium Clostridium acetobutylicum.", J Bacteriol, 2001 Aug;183(16):4823-38

Keis, S., Shaheen, R., and Jones, D.T. "Emended descriptions of Clostridium acetobutylicum and Clostridium beijerinckii, and descriptions of Clostridium saccharoperbutylacetonicum sp. nov. and Clostridium saccharobutylicum sp. nov." Int. J. Syst. Evol. Microbiol. (2001) 51:2095-2103.


Edited by Mark Hower, student of Rachel Larsen and Kit Pogliano