Biochemical and genetic characterization of dehydrobiotin resistant mutants of Escherichia coli

Biotin Synthesis in Ralstonia eutropha H16 Utilizes Pimeloyl Coenzyme A and Can Be Regulated by the Amount of Acceptor Protein

The biotin metabolism of the Gram-negative facultative chemolithoautotrophic bacterium Ralstonia eutropha (syn. Cupriavidus necator), which is used for biopolymer production in industry, was investigated. A biotin auxotroph mutant lacking bioF was generated, and biotin depletion in the cells and the minimal biotin demand of a biotin-auxotrophic R. eutropha strain were determined. Three consecutive cultivations in biotin-free medium were necessary to prevent growth of the auxotrophic mutant, and 40 ng/ml biotin was sufficient to promote cell growth. Nevertheless, 200 ng/ml biotin was necessary to ensure growth comparable to that of the wild type, which is similar to the demand of biotin-auxotrophic mutants among other prokaryotic and eukaryotic microbes. A phenotypic complementation of the R. eutropha ΔbioF mutant was only achieved by homologous expression of bioF of R. eutropha or heterologous expression of bioF of Bacillus subtilis but not by bioF of Escherichia coli Together with the results from bioinformatic analysis of BioFs, this leads to the assumption that the intermediate of biotin synthesis in R. eutropha is pimeloyl-CoA instead of pimeloyl-acyl carrier protein (ACP) like in the Gram-positive B. subtilis Internal biotin content was enhanced by homologous expression of accB, whereas homologous expression of accB and accC2 in combination led to decreased biotin concentrations in the cells. Although a DNA-binding domain of the regulator protein BirA is missing, biotin synthesis seemed to be influenced by the amount of acceptor protein present.IMPORTANCERalstonia eutropha is applied in industry for the production of biopolymers and serves as a research platform for the production of diverse fine chemicals. Due to its ability to grow on hydrogen and carbon dioxide as the sole carbon and energy source, R. eutropha is often utilized for metabolic engineering to convert inexpensive resources into value-added products. The understanding of the metabolic pathways in this bacterium is mandatory for further bioengineering of the strain and for the development of new strategies for biotechnological production.

Cloning and characterization of biotin biosynthetic genes of Kurthia sp

The biotin biosynthesis genes of Kurthia sp., which is an aerobic gram-positive bacterium, were cloned from Kurthia sp. 538-KA26 and characterized. Eleven biotin biosynthetic genes have been identified in Kurthia sp. Kurthia sp. has two genes coding for KAPA synthase, bioF and bioFII, and also has two genes coding for BioH protein, bioH and bioHII. In addition, three genes, orf1, orf2, and orf3, whose functions are unknown, were found in the biotin gene clusters of Kurthia sp. The bioA, bioD, and orf1 genes are arranged in a gene cluster in the order orf1bioDA, and the bioB, bioF, and orf2 genes are arranged in a gene cluster in the order orf2bioFB. These gene clusters proceed to both directions; the face to face promoters and two 40-bp of palindrome sequences exist upstream of the orf1 and orf2 genes. The bioC, bioFII, and bioHII genes are arranged in a gene cluster in the order bioFIIHIIC; a 40-bp of palindrome sequence exists upstream of the bioFII gene. The bioH and orf3 genes are arranged in a gene cluster in the order bioHorf3; a palindrome sequence was not found upstream of the bioH gene. These palindrome sequences are extremely similar to each other, suggesting that the orf1bioDA, orf2bioFB, and bioFIIHIIC gene clusters are regulated by biotin. Kurthia sp. does not have the bioW gene coding pimeloyl-CoA synthase, suggesting that pimeloyl-CoA may be produced by a different pathway than that of gram-positive bacterium B. subtilis or B. sphaericus, further suggesting a modified fatty acid synthesis pathway via acetyl-CoA instead as E. coli has.

Linkage map of Escherichia coli K-12, edition 10: the traditional map

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

Cloning and characterization of the Bacillus subtilis birA gene encoding a repressor of the biotin operon

The Bacillus subtilis birA gene, which regulates biotin biosynthesis, has been cloned and characterized. The birA gene maps at 202 degrees on the B. subtilis chromosome and encodes a 36,200-Da protein that is 27% identical to Escherichia coli BirA protein. Three independent mutations in birA that lead to deregulation of biotin synthesis alter single amino acids in the amino-terminal end of the protein. The amino-terminal region that is affected by these three birA mutations shows sequence similarity to the helix-turn-helix DNA binding motif previously identified in E. coli BirA protein. B. subtilis BirA protein also possesses biotin-protein ligase activity, as judged by its ability to complement a conditional lethal birA mutant of E. coli.

Isolation of Bacillus sphaericus biotin synthesis control mutants: evidence for transcriptional regulation of bio genes

The genes involved in biotin synthesis have recently been isolated from Bacillus sphaericus [Gloeckler et al., Gene 87 (1990) 63-70]. Sequence analysis revealed that they are organized into two gene clusters, designated bioXWF and bioDAYB. The 5'-noncoding region of the bioD locus fused to the xylE reporter gene was inserted into the Gram-positive pUB110 replicon and the resulting plasmid was introduced into B. sphaericus IFO3525. Transformants expressed the xylE gene only if the biotin concentration in the growth medium remained below 50 ng/ml. After mutagenesis, colonies were screened for their ability to express the chromogenic marker in the presence of an excess of biotin. Most of these mutants escaped biotin repression of xylE gene expression. Classical genetic analysis showed they formed two main categories: chromosomal mutations, pleiotropically acting in trans on both bioXWF and bioDAYB 5'-noncoding regions, in which a 15-bp region common to both promoters represented a hot-spot for the second class of plasmid-associated mutations. These results, completed by the identification of transcription start points for the bioD and bioX genes, strongly suggest that this 15-bp sequence overlaps the site of a biotin-mediated negative regulation circuit controlling the transcription of the bio genes.

Nucleotide sequence of the birA gene encoding the biotin operon repressor and biotin holoenzyme synthetase functions of Escherichia coli

A 2.2-kb region of DNA containing the birA gene of Escherichia coli has been sequenced. The birA gene sequence predicts a 35.3-kDal [321 amino acids (aa)] bifunctional protein containing biotin-operon-repressor and biotin-holoenzyme-synthetase activities. Mutations, generated by random insertion of XhoI linkers, defined the extent of the gene. Mutations affecting one or more of five discernable properties of birA [Barker, D. and Campbell, A., J. Bacteriol., 143 (1980) 789-800] were mapped. Three mutations that result in temperature-sensitive (ts) growth, birA85, birA215, and birA879 mapped in the N-terminal two-thirds of the protein. The birA352 mutation, which partially complements birA215 and birA879, maps in the N-terminal third of the protein. Finally, birA361 maps closest to the amino terminus.