Not your typical science blog, but an 'open science' research blog. Watch me fumbling my way towards understanding how and why bacteria take up DNA, and getting distracted by other cool questions.
Negative results (no transformants)
There's no evidence of transformation of either strain by any of the markers. As expected, the C600 strain produced Lac+ revertants (frequency 10^5 - 10^6) and Leu+ revertants (frequency 10^6 - 10^7). I know these are revertants because the control cells (no DNA or no sxy insert or no inducer) produced just as many Lac+ and Leu+ colonies as the cells given DNA, sxy and inducer. The thr-1 mutation didn't revert detectably (frequency <10^8) style="font-style: italic;">lacZ gene.
I know the plates used for the selection were OK because the donor strain (w3110) grows fine on all of them but the recipients don't. This also confirms that the donor strain carries the expected wildtype alleles of lac, leu and thr.
So what next? First the RA and I need to discuss her latest results checking out the crp::kan marker she's been using for her (apparently successful) transformations. Then I'll probably do another set of transformations and controls, this time with that marker.
Waiting for the colonies to grow
Experiment plans
The first step is to inoculate strain W3110 into, say, 10 ml of LB broth and grow it overnight, and then tomorrow morning do a DNA prep. This will be the donor DNA for my transformations.
I'll be transforming two strains, C600 and BW25113. C600 is a work-horse strain from my grad-school days; genetically it is lacY (it can't take up lactose), thi (it needs the vitamin thiamine in its medium), and thr leu (needs the amino acids threonine and leucine in its medium). Its full genotype is F- tonA21 thi-1 thr-1 leuB6 lacY1 glnV44 rfbC1 fhuA1 λ-. F- and λ- means it differs from the ancestral K-12 strain in lacking the conjugative plasmid F and the lambda prophage. The tonA21 mutation removes a protein used as a receptor by phage T1, the glnV44 mutation (also called supE44) changes a glutamine tRNA gene so it inserts its glutamines at what would be UAG stop codons, rfbC catalyzes a step in synthesis of the outer-membrane sugar rhamnose, and fhuA helps cells take up ferrichrome (an iron-scavenging siderophore). I've listed all these because I want to make sure I've thought about all the factors that might confound my experiments - I see none here.
The other strain, BW25113, comes from Barry Wanner by way of the fantastic Keio group in Japan who have generated many of the E. coli clones and cassette mutants we've used. Its full genotype is F- ∆(araD-araB)567, ∆lacZ4787(::rrnB-3), lambda-, rph-1, ∆(rhaD-rhaB)568, hsdR514. So it has deletions of the araBAD operon (can't use arabinose) and the rhaBAD operon (can't take up rhamnose). rph-1 helps processing of tRNAs, and hsdR is a restriction nuclease that cuts DNA lacking a specific methylation.
What controls will I want to do? No DNA, to confirm that I'm seeing transformants and not new mutants. Cells without the inducing sxy gene (with a no-insert version of the plasmid). Cells with the sxy plasmid but without IPTG induction.
What will I select for? In BW25113 I can only select for Lac+, so I'll need minimal plates with lactose as well as minimal plates with glucose. BW25113 doesn't need any supplements. In C600 I can select for Lac+ by providing lactose as the only sugar, but the plates need to be supplemented with thiamine, threonine and leucine. I can also select for Thr+ and for Leu+ by not adding these amino acids to the medium.
So I'll need stocks of glucose and lactose (20%, I think - it's been a very long time since I did simple genetics in E. coli) and of threonine and leucine (10 mg/ml is standard for amino acids, I think). Thiamine I might as well put into all the agar. And minimal salts, and autoclaved agar.
Because I'll be growing up cells with both the inducing plasmid and a no-insert plasmid, I can also follow their growth in enough detail to see whether the insert slows growth.
No real results yet
Today's experiment
Results of UV-sensitivity tests
This suggests that our DH5alpha strains are not really RecA-. That would be consistent with the RA's results in her transformation assays, but it seems unlikely that both our stocks are not what they're supposed to be.
Another weird result is that when DH5alpha is carrying a low-copy sxy expression plasmid it becomes as UV-sensitive as NM554. But the UV-sensitivity of the Rec+ strain BW25113 isn't altered by the same plasmid. (sxy expression in these cells wasn't induced with IPTG, but that may not matter because DH5alpha is deleted for lacZYA and maybe also lacI.)
I guess I should check other components of the genotype of our DH5 alpha strains before I start emailing the RecA experts for advice. It's supposed to be F-, φ80dlacZΔM15, Δ(lacZYA-argF) U169, deoR, recA1, endA1, hsdR17(rk-, mk+), phoA, supE44, λ-, thi-1, gyrA96, relA1. Easy to check for Lac- (the RA just made some MacConkey plates), but many E. coli strains are Lac- so that's not very diagnostic. Hmmm....
What I love about doing E. coli genetics
Photo documentation
This is an iphone snap of my test plate after overnight incubation. The first and third streaks are a recA+ control strain and the second and fourth are of a known recA- strain. Because I was working at an odd angle, the green lines I drew to guide the exposures aren't lined up with the actual exposures. The recA+ cells grew fine after 5 seconds of UV, and gave a few colonies even after 1 minute (probably cells that were shielded in some way from the UV). The recA- cells grew fine when they were not exposed to any UV, but didn't grow at all even after only 5 seconds UV.
So today I've streaked all the cells I want to test, each on at least 2 different plates. I also reduced the UV dose. Yesterday I used a high dose range (5, 15, 30 and 60 seconds) to make sure I had a dose that would kill the recA- cells; today I used 2, 5 10 and 15 seconds.
Doing an experiment at last!
What's done, what's not
- Analysis of the true consensus and variation in uptake sequence motifs in all the bacterial genomes that have uptake sequences (= the family Pasteurellaceae (USS) and the genus Neisseria (DUS)).
- Analysis of variation in DUS and USS motifs across different location categories (orientation wrt replication, in coding sequences, in non-coding sequences, in terminator positions).
- Analysis of covariation between the different positions of the DUS and USS uptake sequence motifs (e.g. does having a particular base at one position correlate with having a particular base at another position).
- Additional experimental data on how variation in uptake sequence affects uptake by H. influenzae. (This will just be a paragraph as it only modestly enriches a previously published dataset.)
- Development of a computer-simulation model of uptake sequence evolution, and use of it to investigate the roles of key factors in maintaining uptake sequences in the non-coding parts of genomes.
The Perl-model manuscript (and the data) still need lots of work
- Analysis of the true consensus and variation in uptake sequence motifs in all the bacterial genomes that have uptake sequences (= the family Pasteurellaceae (USS) and the genus Neisseria (DUS)).
- Analysis of variation in DUS and USS motifs across different location categories (in coding sequences, in non-coding sequences, in terminator positions).
- Analysis of covariation between the different positions of the DUS and USS uptake sequence motifs (e.g. does having a particular base at one position correlate with having a particular base at another position).
- Additional experimental data on how variation in uptake sequence affects uptake by H. influenzae. (This will just be a paragraph as it only modestly enriches a previously published dataset.)
- Development of a computer-simulation model of uptake sequence evolution, and use of it to investigate the roles of key factors in maintaining uptake sequences in the non-coding parts of genomes.
Excavated documents
I now remember that the stuff in the pile on the floor was there for a reason. It's all sources of important ideas that I keep forgetting about - either papers I've read that tell me things I really want to remember, or notes from previous research that should someday be followed up on. Filing them would have almost the same effect as just throwing them out. This way I periodically go through the pile hoping to tidy it away but instead discovering that I need to keep these things where I'll see them now and then.
So what did I find? (Maybe if I blog about them I can decide how to use some of them?) Starting from the top of the research notes pile:
- The table of contents of part of a former tech's lab notebook, indexing the DNA uptake experiments she had done.
- A table listing the H. influenzae strains in a 'tiling-path' collection that a colleague had given us, with a map of the large-insert plasmid they're in. These are cloned in E. coli, and I think I was planning to use them to test whether H. influenzae competence genes work in E. coli (maybe make E. coli competent). I should mention these to the RA when we sit down on Tuesday to discuss the E. coli transformation experiments.
- The abstract of a paper reporting that RadC (competence-induced in S. pneumoniae, H. influenzae and E. coli) does not contribute to transformation or DNA repair in S. pneumoniae. This belongs in the pile of articles, next to one showing that RadC contributes to replication-fork stabilization (highly relevant to our ideas about what else the 'competence' regulons control).
- A very old (c. 1992?) folder containing restriction maps of some plasmids we made with the H. influenzae cya gene. I think these could be filed away.
- A table summarizing 'Next-Generation Sequencing Informatics', printed four months ago and probably already out of date. But highly relevant to the new post-doc's research and our planned NIH proposal.
- A list of the research questions we hoped to answer by microarray analysis of H. influenzae gene expression (also c. 1992). We've certainly answered most of these, but perhaps not all. Certainly I can't remember the answers to some.
- An unpublished summary of research some colleagues did into the distribution of transformability in H. influenzae strains. I think it was presented as a poster about 4 years ago. They sent us the strains, and a former post-doc included some of them in her more detailed analysis of the distrobtuion of competence and transformability (now in press in Evolution).
- Notes from my analysis of PTS genes in Pasteurellaceae, particularly the glucose and fructose transporters. Of interest because the PTS regulates cAMP which regulates competence, and the H. influenzae PTS has only the fructose transporter.
- The reviewers' comments on a manuscript that the former post-doc is revising.
- A page of notes from last summer (or the summer before last) when I was planning to test conditions that might induce E. coli sxy by assaying for expression of two lacZ fusions (to comA and ppdA). I did this and saw no induction.
One manuscript accepted, another resubmitted
NIH programs
CMYK - the saga continues
Tne Sxy in E. coli manuscript
Instead I found lots of problems, so she and I have spent much of the last 10 days revising and re-polishing the sentences, and changing parts of the text, and completely replacing the Discussion, and making the figures clearer. Finally we have a version to send to the former post-doc for final approval. We think it's now quite good, and we certainly don't want to d any more writing, so he's been strictly warned that he's not allowed to make any substantive changes to the text, except maybe to the Discussion, which still needs a final paragraph.
Here's hoping we can submit this one on Monday.
CMYK!
Unfortunately the journal wants the files in CMYK format, but we made the figures with PowerPoint, which doesn't do CMYK. I spent much of yesterday evening looking for a way to convert them that didn't involve PhotoShop. I don't want to buy PhotoShop because it's far too sophisticated and complex for our needs, and it's very expensive.
So first I Googled the problem, but didn't find any easy free solutions. Then I tried my test version of the program Acorn, which costs less than 10% of what Photoshop costs but claims to do most of the same things, only easier. But Acorn can't convert files to CMYK. Then I Googled some more, and found that Macs come with a utility application called ColorSync that claims to do this. So I spent quite a while figuring out how, and doing it, only to discover that the CMYK files became their negatives every time they were saved. Everything goes black except the text, which goes white. The colours don't exactly go black, but they become very dark.
So then I emailed the former post-doc who had mastered these file conversions, and he said he'd had the same problem with ColorSync, but had done CMYK conversions using an old copy of Photoshop on one of our computers. I found our old copy of Photoshop Elements on that computer (it came free with a scanner), but it refused to open. The RA said she has Photoshop (no, wait, it's on the home computer), and that it's also on another old computer. That was again Photoshop Elements, and it did open. But when I tried to use it on my files, there was no CMYK option, and further Googling revealed that Photoshop Elements doesn't support CMYK at all.
I'd really like to get this done today, because the journal wants the resubmission by today so they can include it in their inaugural issue. So I think I'll ask around to see if someone else has a copy of Photoshop I can use for a little while.