O2-Sensing and O2-dependent gene regulation in facultatively anaerobic bacteria
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© Springer-Verlag 1995
MINI-REVIEW
G. Unden · S. Becker · J. Bongaerts · G. Holighaus · J. Schirawski · S. Six
O2-Sensing and O2-dependent gene regulation in facultatively anaerobic bacteria
Received: 10 April 1995 / Accepted: 28 May 1995
Abstract Availability of O2 is one of the most important regulatory signals in facultatively anaerobic bacteria. Various two- or one-component sensor/regulator systems control the expression of aerobic and anaerobic metabolism in response to O2. Most of the sensor proteins contain heme or Fe as cofactors that interact with O2 either by binding or by a redox reaction. The ArcA/ArcB regulator of aerobic metabolism in Escherichia coli may use a different sensory mechanism. In two-component regulators, the sensor is located in the cytoplasmic membrane, whereas one-component regulators are located in the cytoplasm. Under most conditions, O2 can readily reach the cytoplasm and could provide the signal in the cytoplasm. The transcriptional regulator FNR of E. coli controls the expression of many genes required for anaerobic metabolism in response to O2. Functional homologs of FNR are present in facultatively anaerobic Proteobacteria and presumably also in gram-positive bacteria. The target genes of FNR are mostly under multiple regulation by FNR and other regulators that respond to O2, nitrate, or glucose. FNR represents a ‘one-component’ sensor/regulator and contains Fe for signal perception. In response to O2 availability, FNR is converted reversibly from the aerobic (inactive) state to the anaerobic (active) state. Experiments suggest that the Fe cofactor is bound by four essential cysteine residues. The O2-triggered transformation between active and inactive FNR presumably is due to a redox reaction at the Fe cofactor, but other modes of interaction cannot be excluded. O2 seems to affect the site-specific DNA binding of FNR at target genes or the formation of an active transcriptional complex with RNA polymerase. Key words FNR · Anaerobic gene regulation · Oxygen · Facultative anaerobic metabolism · Anaerobic respiration
G. Unden (Y) · S. Becker · J. Bongaerts · G. Holighaus · J. Schirawski · S. Six Institut für Mikrobiologie und Weinforschung, Universität Mainz, Becherweg 15, D-55099 Mainz, Germany Tel. +49–6131–393550; Fax +49–6131–392695 e-mail [email protected]
Biological role of facultative anaerobic metabolism Facultatively anaerobic metabolism is wide-spread among bacteria and archaea, including purple phototrophic (proteo-) and gram-positive bacteria and halophilic or thermophilic archaea (see review by Unden et al. 1994). Catabolism and anabolism are affected by the switch from aerobic to anaerobic growth (Unden et al. 1994). In catabolism, aerobic respiration is replaced by anaerobic respiration, phototrophic growth, or fermentation. Changed expression of enzymes necessitates adaptation of the synthesis of coenzymes and cofactors, such as quinones, hemes, or molybdenum cofactor (Unden 1988; Rivers et al. 1993; Darie and Gunsalus 1994; Unden et al. 1994). Bi
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