Field of Science

Ancient mutants

While searching the -80 °C freezer for a missing chemical I discovered a box of H. influenzae competence mutants from 1970.  Well, I didn't freeze them in 1970, but they were originally isolated in 1970 (Castor, Postel and Goodgal, 1970 Nature 227: 515-517).  The paper gives specific information about only a few of the mutants they isolated, but the strain names go up to com-110 and a later paper refers to 70 independent isolates with abnormally low transformation frequencies.

Unfortunately, none of the strains I found (com-14, -15, -22, -23, -34, -37, -45, -47, -51 and -89) were mentioned in the 1970 paper.  If this had been a new paper, the data for all the mutants wold have been in a supplementary (online-only) table), but not 40 years ago.  So I tracked down later papers from the same group, hoping to find more information about the mutants.  I did find follow-up papers, but not much about the particular mutants I have.  One mutant (com-47) was included in a set whose DNA uptake and recombination were investigated in more detail; it takes up some DNA but not as much as wildtype.  None of these mutants were included in a group whose sensitivity to DNA damage was studied.

One of the mutants, com-51, did get a paper all to itself (Concino and Goodgal 1982  J. Bacteriol. 152:441-450).  The paper reports that the mutant cells produced normal or near-normal amounts of membrane-associated DNA-binding material when competence was induced, but this material did not remain on the cell surface.  Instead it was released into the culture medium as membrane vesicles.  The data doesn't look particularly compelling - for example, the culture medium from these cells is reported to bind H. influenzae DNA (721 cpm of 3H-DNA) but not E. coli DNA (0 cpm), but 721 cpm is only 50% above the H. influenzae DNA background (1431 cpm).  But the mutant might be useful for our work on uptake proteins and uptake specificity, even though we don't know anything about the responsible mutation (or mutations - the cells were heavily mutagenized).

In a 1981 paper the authors also characterized this mutant's phenotype and examined the cell-surface proteins it produced when competent.  Its DNA uptake was 3% of wildtype, and transformation was undetectable (<5x10^7).  The gel  analysis of iodinated surface proteins doesn't show any significant differences between wildtype and com-51.

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