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Spo0A directly controls the switch from acid to solvent production in solvent-forming clostridia (2000)

Ravagnani, Adriana ; Jennert, Katrin C. B. ; Steiner, Elisabeth ; [et al.]

Oxford, UK : Blackwell Science Ltd

Molecular microbiology 37 (2000), S. 0

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ISSN: 1365-2958

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: The spo0A genes of Clostridium beijerinckii NCIMB 8052 and Clostridium cellulolyticum ATCC 35319 were isolated and characterized. The C-terminal DNA-binding domains of the predicted products of spo0A from these two organisms, as well as 16 other taxonomically diverse species of Bacillus and Clostridium, show extensive amino acid sequence conservation (56% identity, 65% similarity over 104 residues). A 12-amino-acid motif (SRVERAIRHAIE) that forms the putative DNA recognition helix is particularly highly conserved, suggesting a common DNA target. Insertional inactivation of spo0A in C. beijerinckii blocked the formation of solvents (as well as spores and granulose). Sequences resembling Spo0A-binding motifs (TGNCGAA) are found in the promoter regions of several of the genes whose expression is modulated at the onset of solventogenesis in Clostridium acetobutylicum and C. beijerinckii. These include the upregulated adc gene, encoding acetoacetate decarboxylase (EC 4.1.1.4), and the downregulated ptb gene, encoding phosphotransbutyrylase (EC 2.3.1.c). In vitro gel retardation experiments using C. acetobutylicum adc and C. beijerinckii ptb promoter fragments and recombinant Bacillus subtilis and C. beijerinckii Spo0A suggested that adc and ptb are directly controlled by Spo0A. The binding affinity was reduced when the 0A boxes were destroyed, and enhanced when they were modified to conform precisely to the consensus sequence. In vivo analysis of wild-type and mutagenized promoters transcriptionally fused to the gusA reporter gene in C. beijerinckii validated this hypothesis. Post-exponential phase expression from the mutagenized adc promoter was substantially reduced, whereas expression from the mutagenized ptb promoter was not shut down at the end of exponential growth.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2958.2000.02071.x

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Selection in chemostat culture of a mutant strain of Clostridium tyrobutyricum improved in its reduction of ketones (1991)

Tidswell, Edward C. ; Thompson, Angus N. ; Gareth Morris, J.

Springer

Applied microbiology and biotechnology 35 (1991), S. 317-322

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ISSN: 1432-0614

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology

Notes: Summary Growth of Clostridium tyrobutyricum on mannitol was possible only when an ancillary oxidant was additionally supplied. Hexacyanoferrate(III) in the presence of methylviologen could fulfil this role, which is normally better accomplished by acetate (and some other organic electron acceptors including acetoin, crotonate and 3-hydroxybutyrate). Several ketones, including pentan-2-one, although slowly reducible by the organism were unable to support its batch culture growth on mannitol. However, when a chemostat culture supplied with excess mannitol but limiting acetate was supplemented with pentan-2-one, a spontaneous mutant strain was selected that was much improved in its specific rate of reduction of this and other ketones, and which was capable of batch growth on mannitol plus pentan-2-one. This procedure may more generally be employed to select strains of anaerobic bacteria improved in their bioreductive abilities.