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A mitochondrial-like aconitase in the bacterium Bacteroides fragilis: implications for the evolution of the mitochondrial Krebs cycle.

ABSTRACT: Aconitase and isocitrate dehydrogenase (IDH) enzyme activities were detected in anaerobically prepared cell extracts of the obligate anaerobe Bacteroides fragilis. The aconitase gene was located upstream of the genes encoding the other two components of the oxidative branch of the Krebs cycle, IDH and citrate synthase. Mutational analysis indicates that these genes are cotranscribed. A nonpolar in-frame deletion of the acnA gene that encodes the aconitase prevented growth in glucose minimal medium unless heme or succinate was added to the medium. These results imply that B. fragilis has two pathways for alpha-ketoglutarate biosynthesis-one from isocitrate and the other from succinate. Homology searches indicated that the B. fragilis aconitase is most closely related to aconitases of two other Cytophaga-Flavobacterium-Bacteroides (CFB) group bacteria, Cytophaga hutchinsonii and Fibrobacter succinogenes. Phylogenetic analysis indicates that the CFB group aconitases are most closely related to mitochondrial aconitases. In addition, the IDH of C. hutchinsonii was found to be most closely related to the mitochondrial/cytosolic IDH-2 group of eukaryotic organisms. These data suggest a common origin for these Krebs cycle enzymes in mitochondria and CFB group bacteria.

SUBMITTER: Baughn AD

PROVIDER: S-EPMC123704 | biostudies-literature | 2002 Apr

REPOSITORIES: biostudies-literature

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A mitochondrial-like aconitase in the bacterium Bacteroides fragilis: implications for the evolution of the mitochondrial Krebs cycle.

Baughn Anthony D AD Malamy Michael H MH

Proceedings of the National Academy of Sciences of the United States of America 20020305 7

Aconitase and isocitrate dehydrogenase (IDH) enzyme activities were detected in anaerobically prepared cell extracts of the obligate anaerobe Bacteroides fragilis. The aconitase gene was located upstream of the genes encoding the other two components of the oxidative branch of the Krebs cycle, IDH and citrate synthase. Mutational analysis indicates that these genes are cotranscribed. A nonpolar in-frame deletion of the acnA gene that encodes the aconitase prevented growth in glucose minimal medi ...[more]

PMID: 11880608

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Project description:Enterotoxigenic Bacteroides fragilis (ETBF) strains, which produce a 20-kDa zinc metalloprotease toxin (BFT), have been associated with diarrheal disease in animals and young children. Studying a collection of ETBF and nontoxigenic B. fragilis (NTBF) strains, we found that bft and a second metalloprotease gene (mpII) are contained in an approximately 6-kb pathogenicity island (termed B. fragilis pathogenicity island or BfPAI) which is present exclusively in all 113 ETBF strains tested (pattern I). Of 191 NTBF strains, 100 (52%) lack both the BfPAI and at least a 12-kb region flanking BfPAI (pattern II), and 82 of 191 NTBF strains (43%) lack the BfPAI but contain the flanking region (pattern III). The nucleotide sequence flanking the left end of the BfPAI revealed a region with the same organization as the mobilization region of the 5-nitroimidazole resistance plasmid pIP417 and the clindamycin resistance plasmid pBFTM10, that is, two mobilization genes (bfmA and bfmB) organized in one operon and a putative origin of transfer (oriT) located in a small, compact region. The region flanking the right end of the BfPAI contains a gene (bfmC) whose predicted protein shares significant identity to the TraD mobilization proteins encoded by plasmids F and R100 from Escherichia coli. Nucleotide sequence analysis of one NTBF pattern III strain (strain I-1345) revealed that bfmB and bfmC are adjacent to each other and separated by a 16-bp GC-rich sequence. Comparison of this sequence with the appropriate sequence of ETBF strain 86-5443-2-2 showed that in this ETBF strain the 16-bp sequence is replaced by the BfPAI. This result defined the BfPAI as being 6,036 bp in length and its precise integration site as being between the bfmB and bfmC stop codons. The G+C content of the BfPAI (35%) and the flanking DNA (47 to 50%) differ greatly from that reported for the B. fragilis chromosome (42%), suggesting that the BfPAI and its flanking region are two distinct genetic elements originating from very different organisms. ETBF strains may have evolved by horizontal transfer of these two genetic elements into a pattern II NTBF strain.

Dataset Information

A mitochondrial-like aconitase in the bacterium Bacteroides fragilis: implications for the evolution of the mitochondrial Krebs cycle.

Publications

A mitochondrial-like aconitase in the bacterium Bacteroides fragilis: implications for the evolution of the mitochondrial Krebs cycle.

Similar Datasets

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