Anaerobic expression of thegyrAgene demonstrated by β-galactosidase activity ingyrA::Mu-lacfusion derivatives ofEscherichia coli

Abstract

E. coli C600Δlac was infected with a Mu‐lac defective phage. Lysogens resistant to ampicillin (25 μg/ml) and nalidixic acid (20 μg/ml) were unable to grow anaerobically and insensitive to nalidixic acid (150 μg/ml), indicating formation of gyrA::Mu‐lac fusions. Mapping of the Mu‐lac by P1 phage cotransduction with two different gyrA linked Tn10 transposon loci suggests that the insertion is located in the gyrA gene. These fusion derivatives form small uncolored colonies on lactose MacConkey agar plates aerobically. When these plates are placed in an anaerobic jar for about 4 h, the colonies turn red indicating that the inserted lac gene is expressed only under anaerobic environment. Thus the gyrA promoter is activated under the anaerobic environment and loss of gyrA activity prevents anaerobic cell growth.

Discoordinate gene expression of gyrA and gyrB in response to DNA gyrase inhibition in Escherichia coli

“…With the concentrations mentioned above the best inductions of DNA gyrase were obtained. The minimal inhibitor concentrations in vitro for DNA gyrase purified from strain KAlO or IGBZll (NEUMANN et al, unpublished results) were almost indistinguishable from those of the literature (DRLICA 1984, DRLICA and FRANC0 1988, ZIMMER et al 1990.…”

“…Whereas the quinolones inhibit both the supercoiling and the relaxing activities of DNAgyrase by blocking the action of the GyrAprotein, the coumarins only inhibit its supercoiling activity by blocking the ATPase reaction of the GyrB protein, so that further relaxation of DNA can occur. This may be possible, because DNA gyrase is able to relax supercoiled DNA in the absence of ATP (DRLICA and FRANCO 1988, ZIMMER et al 1990, REECE and MAXWELL 1991, MAXWELL 1993. Another possibility might be that the gyrB promoter in the chromosome is more sensitive than the gyrA promoter to transcription-driven supercoiling alterations as described by the twin-supercoiled-domain model ( LIU and WANG 1987, Wu et al 1988.…”

“…genetic stability than the plasmid constructs. Furthermore, we tested the functionally of the reporter system by examination of DNA gyrase gene expression under anaerobic conditions, because of the fact that anaerobiosis induces gyrase ( YAMAMOTO and DROFFNER 1988). For this purpose the strains IGAZ4 and IGBZll were plated on MCCONKEY lactose agar plates and incubated at 37 "C for 48 hours in an evacuated anaerobic chamber.…”

“…Furthermore, little is known about the mechanisms that operate in environment-mediated alterations of DNA supercoiling and gyrase gene expression (DRLICA 1992). Nevertheless, an induction of gyrA gene expression has been reported to occur by anaerobiosis (YAMAMOTO and DROFFNER 1988) and in connection to the cold shock response 4a J.…”