Beyond Model Organisms The New Biomanufacturing

[THEO] Okay, picture the microbe you learned in grad school. E. coli, maybe baker's yeast. Well-behaved, grows fast, takes up DNA when you ask nicely. Now imagine everything you want to actually build — a bug that eats plastic, survives Mars, desalinates seawater — lives in some organism that does none of that.

[DR. MARA] Right. The workhorses we've optimized for decades are optimized for the lab, not for the job. And the organisms that already do the interesting chemistry — they're what we call non-model. Intractable, in the polite phrasing.

[THEO] Which is such a great, loaded word. Intractable. Like the microbe is being stubborn on purpose.

[DR. MARA] In a sense it is. When you try to move DNA into these organisms, they defend themselves. Restriction-modification systems chop up foreign DNA — that was my whole doctoral world, the bacterial immune arms race. Then even if the DNA survives, it may not replicate, the promoters may not fire, the codons may be wrong. Every barrier that E. coli lacks, a wild organism can have all at once.

[THEO] So the theme today — we're calling it Creatures Worth Meeting — is really about the tools that let us meet them. How do you shake hands with a bacterium that keeps trying to shred your plasmid.

[DR. MARA] And why bother. That's the stakes question. These organisms do things thermodynamically or metabolically that our lab strains simply can't. Cyanobacteria fix carbon from sunlight. Actinobacteria make a staggering fraction of our antibiotics. Extremophiles hold their proteins folded at temperatures or salinities that would cook or crystallize anything else.

[THEO] Let me define a couple of terms for anyone visiting from a different field. A chassis — that's the host organism you engineer, the frame you bolt your genetic circuit onto. And a cell factory is just that chassis put to work making something — a fuel, a drug, a material.

[DR. MARA] And the reason you can't just pick your favorite chassis: the good chemistry and the good genetics rarely live in the same bug. So the arc of this whole area is closing that gap. Building the genetic toolkit out to where the interesting biology already is.

[THEO] So where does the story start?

[DR. MARA] For our purposes, 2020. Fatma and colleagues wrote a review that essentially took inventory. Bacteria, actinobacteria, cyanobacteria, yeasts, fungi — and made the case that with organism-specific genetic tools, especially CRISPR, any of these could become a cell factory.

[THEO] The key word being organism-specific. There's no universal kit.

[DR. MARA] That's the thesis and, honestly, the frustration embedded in it. The review's argument is that intractability is not a wall, it's a to-do list. You characterize the restriction systems, you find promoters that fire, you get a replicating plasmid, you adapt CRISPR for editing. Do the homework per organism.

[THEO] Which sounds exhausting when you say it out loud. Every new bug, start from zero.

[DR. MARA] And that friction is exactly what the next turning point attacks. 2024, de Vries and colleagues — a cloning method. This is where it gets satisfying for anyone who's ever assembled DNA.

[THEO] Okay so — modular cloning, MoClo. The idea is you have standardized DNA parts, promoters, genes, terminators, and you snap them together like a defined set of bricks. Golden Gate assembly uses a type of enzyme that cuts next to its recognition site, so you can design little sticky overhangs and stitch parts in one pot.

[DR. MARA] The catch historically: those overhangs leave scars. Little junk sequences at the seams. And the acceptor plasmid — the backbone your assembly lands in — has to be built for your specific organism ahead of time.

[THEO] So you're stuck waiting on a backbone for whatever weird organism you're targeting.

[DR. MARA] What de Vries did is use SapI, an enzyme that generates three-nucleotide overhangs. Three nucleotides — that's a codon. So you can make your seams land on codon boundaries and get scar-free transcription units. And the clever half, what they call Out-Cloning: you generate the organism-specific acceptor plasmid on demand, from modular parts, rather than having it in hand first.

[THEO] So that's the toolkit becoming portable. 2020 said do the homework per organism; this says here's a faster pencil.

[DR. MARA] Well put. Now the same year, the story branches from tools into targets. Two papers, two very different creatures. First, Roghair Stroud and colleagues in Pseudomonas alloputida KT2440 — a soil bacterium that lives in the rhizosphere, the root zone.

[THEO] And they brought CRISPRi. Which — let me — CRISPRi is CRISPR with the scissors filed off. You use a dead Cas9, dCas9, that still binds where you point it but doesn't cut. It just sits on a gene and blocks transcription. A programmable off-switch instead of an edit.

[DR. MARA] Precisely. They put dCas9 under an inducible promoter, the XylS/Pm system, and integrated it into the chromosome using mini-Tn7 — a transposon tool that drops your cargo at a defined single site. Then delivered the guide RNAs on pSEVA broad-host-range plasmids.

[THEO] And the headline is they did this in the rhizosphere. In situ. Not in a flask.

[DR. MARA] That's the first, to their claim — gene repression by an engineered strain living in the root environment. And they used it to disable pyoverdine.

[THEO] Pyoverdine — the siderophore. The little iron-grabbing molecule bacteria secrete to hoard iron away from competitors.

[DR. MARA] So by switching it off on demand, they could tune the organism's ability to compete for iron in a real microbial community. That's control of an ecological interaction, not just a metabolic pathway. It connects straight back to Fatma — this is the CRISPR toolkit arriving in an organism that actually matters where it lives.

[THEO] And the other branch that year goes cold. Deming's piece on Colwellia.

[DR. MARA] A News and Views, more of a survey than a result, but it earns its place. Colwellia are psychrophiles — cold-lovers — living in sea ice, and the evidence Deming gathers is that they exceed the temperature and metabolic limits we'd predicted for life in the cold.

[THEO] Which is a reminder that before you engineer a creature, you have to be humble about what it can already do. The wild organism keeps outrunning our models.

[DR. MARA] And that humility feeds the most mechanistic entry — the polyextremophile framework, also 2024. It argues that extreme conditions come down to four proximal stresses: reactive oxygen, covalent damage to molecules, protein unfolding, and membrane fluidity going wrong.

[THEO] So instead of treating "hot" and "salty" and "radioactive" as separate problems, you ask what damage they actually cause at the molecular level — and some combinations reinforce each other, some fight.

[DR. MARA] Which lets you predict, rationally, which multi-stress chassis is even buildable. For space in-situ resource use, for industrial fermentation that runs hot and acidic. That's a design principle, not trial and error.

[THEO] And then someone just goes and evolves one. The Synechocystis paper.

[DR. MARA] Adaptive laboratory evolution — ALE. You don't design the mutations; you apply selective pressure over many generations and let the population find its own solution. They pushed Synechocystis, a model cyanobacterium, up to six and a half percent salt.

[THEO] And found the mechanism after the fact — a membrane protein, slr1753, that parks sodium on the cell surface. And they got desalination out of it, and saline soil that suddenly grew plants again. Germination up 184 percent.

[DR. MARA] So there's the through-line. From "make the tools per organism," to portable cloning, to CRISPRi controlling a bug in soil, to a framework for stress, to evolution finding what design hasn't yet. The gap between good chemistry and good genetics keeps narrowing.

[THEO] Creatures worth meeting — and finally worth building. That's our arc. After the break, the mailbag.