Evolution of coenzyme B12 synthesis among enteric bacteria: evidence for loss and reacquisition of a multigene complex

Article Abstract:

Various enteric bacteria were studied to identify differences in cobalamin synthetic ability and cobalamin-dependent metabolism. Majority of the bacteria studied synthesized cobalamin during both aerobic and anaerobic conditions and fermented glycerol in a cobalamin-dependent manner. However, several groups such as Escherichia coli and Salmonella typhimurium were unable to synthesize cobalamin in both conditions. The results suggest that these bacteria had a common ancestor which lost the ability to synthesize cobalamin. In addition, it suggests that Salmonella spp. reacquired the ability through an exogenous source since it is the only bacteria capable of synthesizing cobalamin under anaerobic conditions.

Physiological aspects, Bacteria, Biosynthesis, Coenzymes, Vitamin B12

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Recombination between chromosomal IS200 elements supports frequent duplication formation in Salmonella typhimurium

Article Abstract:

The contribution of insertion sequence 200 (IS200) elements to formation of tandem duplications in Salmonella typhimurium was investigated. S. typhimurium LT2 strains were transduced by phage P22 with a series of transducing lysates. Spontaneous duplications were isolated and detected by genetic mapping of the duplication endpoints. Restriction fragment analysis near the IS200 positions revealed that recombination between IS200 elements accounted for majority of the duplications, particularly of the his operon. It is suggested that IS200 promotes genome rearrangements and increases frequency of homologous recombination between chromosomal IS200 elements.

Genetic aspects, Genetic recombination, Salmonella typhimurium, Insertion elements, DNA, DNA insertion elements

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Lethal transposition of Mud phages in rec- strains of Salmonella typhimurium

Article Abstract:

The frequency of lysogeny by Mud prophages has been noted to be reduced in rec strains of Salmonella thypimurium. When lysogen formation had been reduced by a host of rec mutation, the surviving lysogens have the propensity of having a deletion next to the insertion site which may be due to a failure of conservative Mu transposition. The transposition causes breaks in the host chromosome with Mu prophage at both ends and are considered lethal unless repaired. Repair is done by Rec functions working on the Mu sequences or by secondary transposition events.

Analysis, Translocation (Genetics), Lethal mutation

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