f Powerful methods to establish chromosomal markers in Lactococcus lactis: an analysis of pyrimidine salvage pathway mutants obtained by positive selections
- Authors: Jan Martinussen, Karin Hammer
- Author for correspondence: Jan Martinussen. Tel: +45 45 25 24 98. Fax: +45 45 88 26 60.
- First Published Online: 01 August 1995, Microbiology 141: 1883-1890, doi: 10.1099/13500872-141-8-1883
- Subject: Biochemistry
- Issue Published:
Using different 5-fluoropyrimidine analogues, positive selection procedures for obtaining mutants blocked in pyrimidine and purine salvage genes of Lactococcus lactis were established. Strains lacking the following enzyme activities due to mutations in the corresponding genes were isolated: uracil phosphoribosyltransferase (upp), uridine/cytidine kinase (udk), pyrimidine nucleoside phosphorylase (pdp), cytidine/deoxycytidine deaminase (cdd), thymidine kinase (tdk) and purine nucleoside phosphorylase (pup). Based on an analysis of the mutants obtained, the pathways by which L. lactis metabolizes uracil and the different pyrimidine nucleosides were verified. The substrate specificities of the different enzymes were determined. It was demonstrated that a single pyrimidine nucleoside phosphorylase accounts for the phosphorolytical cleavage of uridine, deoxyuridine and thymidine, and a single purine nucleoside phosphorylase has activity towards both the ribonucleoside and deoxyribonucleoside derivatives of adenine, guanine and hypoxanthine. No phosphorylase activity towards xanthosine appeared to be present. The selection procedures developed during this work may be employed in establishing markers on the chromosome of many related lactic acid bacteria.
- Keyword(s): pyrimidine salvage pathway mutants, Lactococcus lactis, nucleotide metabolism, chromosomal markers, positive selections
© Society for General Microbiology 1995 | Published by the Microbiology Society
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