Inhibitor-associated transposition events in Corynebacterium glutamicum

Abstract

In up to 100% of all bacteria grown in the presence of initially inhibitory concentrations of five diverse inhibitors, an extra copy of the resident insertion element IS 31831 was found in specific chromosomal regions, the sites of which apparently depended on the inhibitor used. Thus, in nine out of nine independently isolated cyanide-associated transpositions, the acquired copy was located within an ORF encoding a protein related to the hypothetical but conserved protein YeiH of Escherichia coli. A putative Sox box upstream of the yeiH gene implicates superoxide as a potential regulator of the gene, a possibility further supported by the finding that superoxide dismutase (SodA) is overexpressed in cells cultured in cyanide-containing medium. Neither the cyanide-associated nor any of the other transposition mutations appeared to confer any discernible phenotypic advantage upon cells grown in the presence or absence of the inhibitors, as revealed most stringently by mixed-cell experiments. An alternative, albeit heterodox, explanation for the emergence of the mutants postulates a very high rate of transpositional activity in the presence of inhibitors. The initial emergence of the mutants was found to depend crucially upon the cell density. Thus, when growth medium was supplemented with 50 mM fluoropyruvate and inoculated to a density of 2 x 10(7) cfu/ml, single colonies with heterogeneous restriction fragment length polymorphisms (RFLPs) were routinely isolated at a frequency of 6 to 16% after 1-2 days of incubation. After 3 days, 10-36% of the colonies showed RFLPs, but the type was now dominated by the fluoropyruvate-specific RFLP, which, at higher resolution, invariably proved to be heterogeneous. This heterogeneity proved that these specific mutants were of multiple origin, indicating that clonal enrichment was irrelevant to their emergence. It is suggested that the presence of the inhibitor induces the development of hyper-transpositional activity, which is regulated by a soluble bacterial product.

Transcriptome Profiling Reveals Interplay of Multifaceted Stress Response in Escherichia coli on Exposure to Glutathione and Ciprofloxacin

“…Being a prominent cellular antioxidant, GSH has a significant influence on the cellular redox state, thereby upregulating the expression of redox function genes such as yeiH and azoR in E. coli as observed using microarray and RT-qPCR methods. Among the genes mentioned above, yeiH has been previously reported to harbor an upstream sox box, showing its potential regulation by the soxRS system ( 14 ), whereas azoR was implicated in thiol-specific stress in a previous study ( 15 ). Genes coding for the Fe citrate transporter ( fecA ) ( 16 ) and for the Fe-S center subunit of fumerate reductase ( frdB ) ( 17 ) are downregulated by GSH, plausibly to avoid the cellular injury that occurs via Fenton reaction-induced ·OH due to elevated cellular Fe ++ levels.…”

A Hypervariable 130-Kilobase Genomic Region of Magnetospirillum gryphiswaldense Comprises a Magnetosome Island Which Undergoes Frequent Rearrangements during Stationary Growth

“…In Mycobacterium smegmatis transposition was stimulated by exposure to microaerobic conditions or a subsequent oxygen shock (16). Induction of hypertranspositional activity by the presence of diverse inhibitors, including cyanide and hydrogen peroxide, was observed in Corynebacterium glutamicum (15). Hydrogen peroxide is known to be a potent inducer of the SOS response which enhances recombinational activity.…”

New Multiple-Deletion Method for the Corynebacterium glutamicum Genome, Using a Mutant lox Sequence

“…However, despite its industrial usefulness, similarly useful techniques have yet to be developed for C. glutamicum. In our laboratory, comprehensive studies on C. glutamicum, including isolation and characterization of new transposable elements and development of Cre/ loxP-mediated genome deletion systems, are being undertaken (7,16,32,33,35,38). The utilization of such techniques could greatly contribute to creation of a C. glutamicum-based MGF.…”