Role of DNA Superhelicity in Regulation of Bacteroid-Associated Functions of Bradyrhizobium sp. Strain 32H1
AUTOR(ES)
Gober, James W.
RESUMO
Bradyrhizobium sp. strain 32H1 cells express a number of bacteroid-associated functions and repress some functions related to the free-living state when grown ex planta under conditions of low (0.2%) oxygen tension and relatively high levels (>8 mM) of medium K+. Expression of the bacteroid-associated phenotype was blocked by the DNA gyrase inhibitor novobiocin. Because the degree of negative supercoiling of DNA is the result of the activities of both DNA gyrase and topoisomerase I, we measured these enzymes in cells grown under nitrogen-fixing (low O2, high K+) and non-nitrogen-fixing conditions (low O2, low [50 μM] K+ or high O2, high K+). Lower topoisomerase I activities were seen in extracts from nitrogen-fixing cells than in those from non-nitrogen-fixing cells. In contrast, DNA gyrase levels were lower in high-O2-grown cells than under the other conditions tested. These differences are consistent with an increase in DNA superhelicity associated with growth under low-O2, high-K+ conditions. A spontaneous mutant resistant to the DNA gyrase inhibitor ciprofloxacin was found to be constitutive with respect to the K+ requirement, because it expressed the bacteroid-associated phenotype when grown under low-O2, low-K+ conditions. The mutant cells gave rise to effective nodules on Macroptilium atropurpureum and possessed the low topoisomerase I activities and high DNA gyrase levels of low-O2-, high-K+-grown wild-type cells. Our data suggest that changes in DNA supercoiling resulting from low O2 tension and a high K+ concentration exert a major influence on the expression of the bacteroid-associated phenotype.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=202881Documentos Relacionados
- K+ regulates bacteroid-associated functions of Bradyrhizobium
- H+/ATP stoichiometry of cowpea Rhizobium sp. strain 32H1 cells grown under nitrogen-fixing and nitrogen-nonfixing conditions.
- Effects of K+ on the proton motive force of Bradyrhizobium sp. strain 32H1.
- Cell surface carbohydrates of microaerobic, nitrogenase-active, continuous cultures of Bradyrhizobium sp. strain 32H1.
- Methylammonium uptake by Rhizobium sp. strain 32H1.