Effects of Novobiocin and Coumermycin on the Biosy...
Since the transcription of various photosynthetic genes including the genes involved in Bchl biosynthesis and the genes for LH proteins is inhibited by novobiocin and coumermycin，the biosynthesis of Bchl and LH complexes must also be inhibited by the drugs，but over a longer time scale.We have examined Bchl content in the presence of the gyrase inhibitors and have shown that the accumulation of Bchl in photoheterotrophically grown cells is strongly inhibited by novobiocin and coumermycin（data not shown）.The Bchl accumulation is inhibited by novobiocin and coumermycin at concentrations as low as 5 μg/ml.Photosynthetic growth was gradually inhibited as the concentration of the inhibitors was increased from 5 μg/ml to 100 μg/ml，although viability of the cells was not affected up to 150 μg/ml（see also Ref.［21］）.The time course of the inhibition of Bchl accumulation indicates that a significant inhibition is observable 30 min after addition of the drugs.
The inhibition of Bchl biosynthesis by the drugs has also been observed in the cells shifted from aerobic to anaerobic photosynthetic conditions.Such a shift is described in the former section.We could detect no growth in our cultures based on optical density measurements at 680 nm during the first 3 h of the induction period with or without the drugs.The Bchl is absent under aerobic conditions.However，the synthesis of Bchl is initiated by the shift to anaerobic conditions in the absence of the drugs and fails to initiate when novobiocin or coumermycin is present.The Bchl content in the control cells was estimated as 1.0 μg/mg of protein after a 3-h induction，whereas Bchl in either novo-biocinor coumermycin-treated cells was not detectable.
The spectra of pigment extracts and chromatophores（data not shown）have also demonstrated that the accumulation of LH-Ⅰ，-Ⅱcomplexes as well as Bchl is markedly inhibited by novobiocin and coumermycin.(https://www.daowen.com)
To further verify the involvement of DNA supercoiling in Bchl accumulation，we have tested two additional inhibitors of gyrase：nalidixic acid（50 μg/ml）and oxolinic acid（50 μg/ml）.A similar inhibition of Bchl accumulation by these drugs was observed（not shown）.
