Field of Science

Sorry for the paucity of posts

The research side of my brain has been devoured by the looming need to teach introductory biology to 450 freshmen (two sections of 225). Last year at this time I was focusing on grant proposal writing, and so I let my teaching coast on the course preparation I'd done the year before (the first year I taught this course). This year I'm trying to make up for last year's neglect, and my brain is struggling to come up with concept maps and personal response system questions and stimulating homework assignments and lecture content that better matches our new learning objectives and classroom activities suitable for large lectures and ...

But I did spend much of the last couple of days working with one of the post-docs on her manuscript about the competence phenotypes of diverse H. influenzae strains. One of the issues that came up about the Discussion is why our standard lab strain is one of the most competent, rather than being more typical of average strains.

Our initial thought was that perhaps, over more than 50 years of lab culture, descendants of the original isolate had been gradually selected for higher and higher competence in lab transformation experiments. That is, each time a transformation was done, variants that had taken up or recombined more DNA would be enriched in the plate of transformed colonies. But such transformants do not replace the original lab stock, but become new lab strains with new names and new places in the freezer. The original strain has (I think) always been maintained as a frozen stock, with individuals occasionally replacing their depleted vials with a new culture grown from descendants of a previous one. Depending on the culture history int eh intervals between thawing the parental stock and freezing a new one, these cells are likely to have been variably but unintentionally selected for improved growth in broth or on agar, of for longer survival after growth had stopped. We have no particular evidence that the ability to take up DNA would have played a significant role in this selection.

But there are other explanations for why the Rd strain is so competent. First, it was not a completely random isolate. The original H. influenzae transformation paper (Leidy and Alexander 1952?) reports testing strains of different serotypes, with Rd being the most competent. Second, if this most-competent isolate had transformed poorly, H. influenzae might not have become the first model organism for studies of competence in gram-negative bacteria.

We'll need to concisely explain this thinking in or Discussion, as a reviewer is likely to raise the issue.

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