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Isolation and Partial Characterization of DNA in Capsular Preparations of Rhizobium trifolii
Author(s) -
WULLSTEIN L. H.,
BRUENING M. L.,
WULLSTEIN B. M.,
SHERWOOD M.
Publication year - 1975
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1975.tb03881.x
Subject(s) - dna , intracellular , biology , thymidine , biochemistry , rhizobium , dna synthesis , bacteria , polysaccharide , nucleic acid , microbiology and biotechnology , genetics , gene
The capsular polysaccharides from thymidine‐(methyl‐ 3 H) labeled cultures of Rhizobium trifolii ; strain 162S7 (Nitragin Co.) were centrifuged from bacterial cells and collected by ethanol precipitation. Following the addition of unlabeled carrier nucleic acids, labeled DNA, termed cap‐DNA, was isolated from the capsular polysaccharides. Cap‐DNA absorbed maximally at H‐260 nm and was DNase sensitive. Approximately 11 μg of 3 H‐cap‐DNA were consistently isolated per liter of 48 h cultures. Cap‐DNA production was generally synchronized with the synthesis of the capsular polysaccharide and bacterial growth, attaining maximum recoverable amounts in 48 h cultures. By five days of culture growth, significant decreases in the amount of recoverable cap‐DNA were noted. The presence of label in the cap‐DNA demonstrated that the cap‐DNA originated via de novo synthesis by the Rhizobium cells rather than from an anomalous source. The cap‐DNA and intracellular Rhizobium DNA had similar buoyant densities of p = 1.719, indicating that cap‐DNA arose specifically from the intracellular DNA. In 48‐h cultures the specific activity of the cap‐DNA was about one‐third that of the intracellular DNA. This implies intracellular DNA was released during early growth with a relatively low specific activity which diluted the isotopic label of DNA released later. The evidence suggests lysogeny was the principal release mechanism.