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Microbiology Society logo - Volume 149, Issue 6, 2003

Volume 149, Issue 6

Volume 149, Issue 6, 2003

  • Physiology

      • Changes in GE2270 antibiotic production in through modulation of methylation metabolism

        https://doi.org/10.1099/mic.0.26157-0

        Thiazolylpeptide GE2270 is a potent antibiotic inhibiting protein synthesis in Gram-positive bacteria. It is produced as a complex of 10 related metabolites, differing mainly in the degree of methylation, by fermentation of the rare actinomycete ATCC 53773. Addition of vitamin B12 to the fermentation medium doubled total complex production and markedly changed the relative production of the various GE2270 metabolites, enhancing the biosynthesis of the more methylated component A. Among methylation inhibitors, the addition of sinefungin increased the amount of factor D2, which differs from component A in the lack of a methyl group. Since sinefungin is an -adenosyl--methionine methyltransferase-specific inhibitor, these results indicate that the methylation step converting D2 into A involves an -adenosyl--methionine methyltransferase. Simultaneous supplementation of vitamin B12 and sinefungin led to a twofold increase in D2 concentration, showing that vitamin B12, in addition to having an effect on the late methylation step, exerts a stimulating action on antibiotic backbone synthesis. This is possibly due to its role in an unusual pathway of serine synthesis peculiar to metabolism. Finally, fermentation medium modifications were shown to be useful for the production of industrially valuable levels of components A or D2 in the GE2270 complex as starting points for the production of new interesting semi-synthetic antibiotics.

    • Characterization of the expression and activity of the periplasmic nitrate reductase of in chemostat cultures

      https://doi.org/10.1099/mic.0.26277-0

      The periplasmic nitrate reductase (Nap) from has a role in cellular redox balancing. Previously, transcription from the promoter in was shown to be responsive to the oxidation state of the carbon substrate. During batch culture, expression was higher during growth on reduced substrates such as butyrate compared to more oxidized substrates such as succinate. In the present study the effect of growth rate on expression in succinate-, acetate- and butyrate-limited chemostat cultures was investigated. In all three cases transcription from the promoter and Nap enzyme activity showed a strong correlation. At the fastest growth rates tested for the three substrates expression and Nap activity were highest when growth occurred on the most reduced substrate (butyrate > acetate > succinate). However, in all three cases a bell-shaped pattern of expression was observed as a function of growth rate, with the highest levels of expression and Nap activity being observed at intermediate growth rates. This effect was most pronounced on succinate, where an approximately fivefold variation was observed, and at intermediate dilution rates expression and Nap activity were comparable on all three carbon substrates. Analysis of mRNA prepared from the succinate-grown cultures revealed that different transcription initiation start sites for the operon were utilized as the growth rate changed. This study establishes a new regulatory feature of expression in that occurs at the level of transcription in response to growth rate in carbon-limited cultures.

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