Interconversion and uptake of nucleotides, nucleosides, and purine bases by the marine bacterium MB22

Abstract

Whole cells and isolated membranes of the marine bacterium MB22 converted nucleotides present in the external medium rapidly into nucleosides and then into bases. Nucleosides and purine bases formed were taken up by distinct transport systems. We found a high-affinity common transport system for adenine, guanine, and hypoxanthine, with a Km of 40 nM. This system was inhibited noncompetitively by purine nucleosides. In addition, two transport systems for nucleosides were present: one for guanosine with a Km of 0.8 ,uM and another one for inosine and adenosine with a Km of 1.4 ,uM. The nucleoside transport systems exhibited both mixed and noncompetitive inhibition by different nucleosides other than those translocated; purine and pyrimidine bases had no effect. The transport of nucleosides and purine bases was inhibited by dinitrophenol or azide, thus suggesting that transport is energy dependent. Inside the cell all of the substrates were converted mainly into guanosine, xanthine, and uric acid, but also anabolic products, such as nucleotides and nucleic acids, could be found. MATERIALS AND METHODS Organism. The marine bacterium MB22 was a kind gift from A. J. De Siervo, University of Maine at Orono. Some of the microbiological characteristics of MB22 were published recently (17). Chemicals. 8-14C-labeled adenine, guanine, hypoxanthine, adenosine, guanosine, AMP, and GMP were obtained from the "Commissariat a l'energie atomique" (Gif-sur-Yvette, France), and 'IC-labeled ino-471

Nucleoside uptake in Vibrio cholerae and its role in the transition fitness from host to environment

“…Expression of VC2352 in a ΔΔΔ mutant not only restored growth back to WT levels, but also resulted in elevated [8‐ 14 C]adenosine accumulation beyond the WT. The determined V max and apparent K m values for [8‐ 14 C]adenosine of the three transporters are close to kinetic constants reported for E. coli K12 or the marine bacterium MB22 (Mygind and Munch, ; Foret and Ahlers, ). Binding protein dependent transport systems, such as maltose or hexose‐6‐phosphate uptake systems, are characterized as high affinity sugar transporters, showing K m values, e.g.…”

“…Data represent median values of at least four independent measurements. Growth parameters analyzed can be found in Table S1. and Ahlers, 1982). Binding protein dependent transport systems, such as maltose or hexose-6-phosphate uptake systems, are characterized as high affinity sugar transporters, showing K m values, e.g.…”