Engineering Unnatural Organisms

[SOFIA] Okay, so here's a question that sounds dumb until you actually try to do it: how do you get a piece of DNA into a cell that doesn't want it? And I mean a cell that really, really doesn't want it.

[DANIEL] Which is most cells, honestly. The ones we work with in labs — E. coli, yeast — those are the weird easy exceptions. They're the lab rats.

[SOFIA] Right, and that's the whole thing I want to trace today. Because the dream in our field — the whole reason you'd care — is that there's this enormous universe of organisms out there doing chemistry we desperately want. Bacteria that eat cellulose. Cyanobacteria that fix carbon straight from sunlight. Fungi that secrete enzymes by the gram.

[DANIEL] And you can't engineer a single one of them if you can't get your DNA across the membrane and have it stick.

[SOFIA] That's the bottleneck. Step zero. So before we even talk about CRISPR, before promoters, before any of the fun circuit stuff — you've got to solve delivery. Let me set some terms, because this trips people up even at the PhD level if it's not your subfield.

[DANIEL] Please, because people say "transfection" and I twitch.

[SOFIA] Yes — so for bacteria and archaea, getting DNA in is called transformation. "Transfection" is a eukaryotic word, reserve it for mammalian cells. In the microbial world you've basically got three doors. Natural transformation, where the cell itself has machinery to suck up DNA from its environment. Conjugation, where another cell physically hands DNA over through a bridge. And electroporation — you hit the cells with an electric field and briefly punch holes in the membrane so DNA slips in.

[DANIEL] And then even if it gets in, the cell can chew it up. Restriction-modification systems — the bacterium's immune memory, basically. It methylates its own DNA and shreds anything that doesn't match the pattern.

[SOFIA] Which is why some organisms are called "recalcitrant." Not because the DNA can't physically enter — because every layer, the wall, the membrane, the enzymes, is fighting you. So the arc I want to walk through is: how did people chip away at delivery across really stubborn organisms, over about twenty-five years?

[DANIEL] Where do you want to start?

[SOFIA] 1994. A filamentous fungus, Aspergillus niger. And the pain here is the cell wall — fungi have this thick chitin-glucan wall. The standard move for decades was protoplasting: you enzymatically strip the whole wall off, leaving a naked, fragile protoplast, then coax DNA in.

[DANIEL] Which is miserable. It's slow, it's finicky, your yields are all over the place.

[SOFIA] So this paper asks: what if we skip it? They took germinating conidia — basically fungal spores that have just started to wake up and grow — intact, wall and all, and just electroporated them. And it worked. About a hundred colonies per microgram of plasmid.

[DANIEL] Hm. A hundred per microgram is not a big number. Let's be honest about that. If you handed me that efficiency in E. coli I'd throw the prep out.

[SOFIA] Totally fair. But the point isn't the magnitude, it's that it worked at all without protoplasting. And they found if you add a little lytic enzyme — just soften the wall, don't remove it — you double it.

[DANIEL] Okay, that I like. That's the useful insight. It's telling you the wall is a real barrier but you don't have to fully demolish it. You can partially weaken it and let the field do the rest. Mechanistically that's a nice middle ground.

[SOFIA] That's the first turning point for me — the idea that the sample prep is the lever, not some fancy new machine. And that theme comes roaring back in 2005. Choi and colleagues, Pseudomonas aeruginosa.

[DANIEL] This one I actually find impressive.

[SOFIA] Okay this is the good stuff — they develop a ten-minute electrocompetent prep. Just quick spins in a microcentrifuge to wash the cells, and they get a ten-thousand-fold improvement in transformation efficiency.

[DANIEL] Four orders of magnitude. From a prep change. And the consequence is what matters: it let them put DNA onto the chromosome directly, by electroporation, instead of relying on conjugation or transduction — using a virus to ferry it in.

[SOFIA] Which were the old workarounds, right? If you couldn't transform cleanly, you'd borrow a phage or do a mating.

[DANIEL] And those are slower and they constrain what you can move. So replacing them with a ten-minute spin — that's the kind of result that quietly changes how a whole community does its daily work. It held up. People adopted it.

[SOFIA] So by the mid-2000s you've got these two case studies screaming the same lesson: prep and partial barrier-softening beat brute force. And then 2009 — Aune and Aachmann sit down and survey the whole zoo of artificial transformation methods in recalcitrant bacteria.

[DANIEL] And the honest conclusion is kind of deflating but important: no method wins. There's no universal protocol.

[SOFIA] Right — you have to match the mechanism to the specific organism's barrier. If restriction-modification is your problem, you solve that. If it's the wall, you solve that. The A. niger and Pseudomonas stories are just two points on a landscape where every organism needs its own answer.

[DANIEL] Which is intellectually unsatisfying and completely true. I appreciate a review that doesn't oversell.

[SOFIA] Now here's where the arc gets weird and I love it. 2012 — mitochondria.

[DANIEL] The organelle. Why are we in the organelle?

[SOFIA] Because it's maybe the hardest delivery target there is, and it turns out the cell already solved it. This paper shows isolated mitochondria — plant and mammalian — actively import double-stranded DNA through a channel called VDAC, the voltage-dependent anion channel on the outer membrane.

[DANIEL] So not punching holes. A native transport protein doing the work.

[SOFIA] And the plant and mammalian cases differ. Plant mitochondrial import also needs ANT — another transporter — and terminal inverted repeats on the DNA, little sequence flags. Mammalian import doesn't need those.

[DANIEL] So same broad trick, different molecular requirements. That rhymes with the 2009 message — conserved problem, organism-specific solution.

[SOFIA] Exactly the through-line. And it reframes delivery completely: instead of forcing DNA in from outside, can we recruit the machinery that's already there? Which brings us to the natural transformation review in 2014 — about eighty bacterial species that take up DNA on their own, sharing conserved uptake proteins but totally divergent rules for when they switch it on.

[DANIEL] And the field's best guess for why they do it is genetic diversity and repairing their own chromosomes — not eating the DNA for food, which was an older hypothesis.

[SOFIA] So the engineering fantasy becomes: find the natural uptake machinery, trigger it on purpose. And that lands us at 2018, the non-model prokaryote toolbox review out of NREL and CU Boulder. Phototrophs, autotrophs, cellulose degraders — organisms with real bioeconomy value, still basically locked.

[DANIEL] And the complaint there is that the design rules are scattered. Everyone's solving it one organism at a time, nobody's synthesized it into something you can hand a newcomer.

[SOFIA] Which is the whole arc in one sentence. Twenty-four years of brilliant one-off tricks, and the frontier now is turning them into general principles — treating the chassis itself as a design variable instead of a given.

[DANIEL] That's the honest state of it. We're good at bespoke. We're not yet good at systematic.

[SOFIA] And that's a great place to leave it. Delivery is still step zero — but we finally know what shape the problem is. More after the break.