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Isolation and characterization of transposon Tn5 mutants of Rhodobacter sphaeroides deficient in both nitrate and chlorate reduction. (1994)

Moreno-Vivián, C. ; Roldán, M.D. ; Reyes, F. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

FEMS microbiology letters 115 (1994), S. 0

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ISSN: 1574-6968

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Abstract The wild-type strain Rhodobacter sphaeroides DSM 158 is a nitrate-reducing bacterium with a periplasmic nitrate reductase. Addition of chlorate to the culture medium causes a stimulation of the phototrophic growth, indicating that this strain is able to use chlorate as an ancillary oxidant. Several mutant strains of R. sphaeroides deficient in nitrate reductase activity were obtained by transposon Tn5 mutagenesis. Mutant strain NR45 exhibited high constitutive nitrate and chlorate reductase activities and phototrophic growth was also increased by the presence of chlorate. In contrast, the stimulation of growth by chlorate was not observed in mutant strains NR8 and NR13, in which transposon Tn5 insertion causes the simultaneous loss of both nitrate and chlorate reductase activities. Tn5 insertion probably does not affect molybdenum metabolism since NR8 and NR13 mutants exhibit both xanthine dehydrogenase and nitrogenase activities. These results that a single enzyme could reduce both nitrate and chlorate in R. sphaeroides DSM 158.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1574-6968.1994.tb06651.x

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Molecular and Regulatory Properties of the Nitrate Reducing Systems of Rhodobacter (1996)

Castillo, F. ; Dobao, M.M. ; Reyes, F. ; [et al.]

Springer

Current microbiology 33 (1996), S. 341-346

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ISSN: 1432-0991

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Abstract. Phototrophic bacteria of the genus Rhodobacter possess several forms of nitrate reductase including assimilatory and dissimilatory enzymes. Assimilatory nitrate reductase from Rhodobacter capsulatus E1F1 is cytoplasmic, it uses NADH as the physiological electron donor and reduced viologens as artificial electron donors, and it is coupled to an ammonium-producing nitrite reductase. Nitrate reductase induction requires a high C/N balance and the presence of nitrate, nitrite, or nitroarenes. A periplasmic 47-kDa protein facilitates nitrate uptake, thus increasing nitrate reductase activity. Two types of dissimilatory nitrate reductases have been found in strains from Rhodobacter sphaeroides. One of them is coupled to a complete denitrifying pathway, and the other is a periplasmic protein whose physiological role seems to be the dissipation of excess reducing power, thus improving photoanaerobic growth. Periplasmic nitrate reductase does not use NADH as the physiological electron donor and is a 100-kDa heterodimeric hemoprotein that receives electrons through an electron transport chain spanning the plasma membrane. This nitrate reductase is regulated neither by the intracellular C/N balance nor by O2 pressure. The enzyme also exhibits chlorate reductase activity, and both reaction products, nitrite and chlorite, are released almost stoichiometrically into the medium; this accounts for the high resistance to chlorate or nitrite exhibited by this bacterium. Nitrate reductases from both strains seem to be coded by genes located on megaplasmids.