The Yeast of Malice and Wickedness

(originally written the day after Christmas)

My grad student Bible study group's doing St. Paul's first letter to the early church in Corinth, usually called 1 Corinthians for brevity's sake. Paul being Jewish uses the metaphor of leavened bread as "contaminated" and flatbread as "holy".

Your boasting is not good. Don't you know that a little yeast works through the whole batch of dough? Get rid of the old yeast that you may be a new batch without yeast—as you really are. For Christ, our Passover lamb, has been sacrificed. Therefore let us keep the Festival, not with the old yeast, the yeast of malice and wickedness, but with bread without yeast, the bread of sincerity and truth.

(reference: 1 Corinthians 5:6-8)

One of the new girls, a first-year student who's doing a rotation in a Saccharomyces lab, starts laughing. "I should label one of my freezer boxes 'The Yeast of Malice and Wickedness'," she says.

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I'm having my own encounter with the Yeast of Malice and Wickedness today. In the morning I pull a flask that I'd seeded with quail fibroblast cells on Christmas eve, wash the layer of cells growing on the plastic with saline, then add some fresh M199 medium. I take another flask that I infected some days ago with my virus, scrape out the cells with a plastic squeegee, burst them to bits with an ultrasonic probe, and pipette a small portion into the new flask. I've done this five times over the past couple of months. Each new flask is infected with virus grown in the last one - this is called "passaging". What I'm trying to do is to get this virus to adapt to growing in cultured cells instead of the chicken embryos it prefers. Whole eggs are messy, fiddly, and largely unusable for genetic engineering purposes. It's a large DNA virus, so they don't evolve quite as fast as some others like the RNA-based ones, but I'm hopeful.

A few hours later, I come in to look at my cells and go OMGWTFBBQ as I realize that the myriad floating bubbles in my flask aren't just fragments of dead cells from the inoculum. For one, they're too small; for another, strangely opaque; also, joined together in short chains of twos and threes. My first thought is bacteria, but they're too small. I groan inwardly, contemplating the necessity of throwing this one away.

"Diana, can you look at this for me?" I ask, baffled.
"This is yeast," she says. "What medium did you use?" We pull the M199 bottle back out of the fridge. The medium is clear, unclouded by growing cells, but I groan again as I recall that I'd dropped the bottle momentarily that morning, letting the medium slosh up into the neck and cap. The cap of any bottle is always to be presumed contaminated, especially since these medium bottles are plastic which can't be flamed (passed through the flame of a Bunsen burner) like a glass flask.

"Maybe you can wash the cells and put fresh medium with antibiotic-antimycotic," she suggests. I do so feeling vaguely guilty. Cross fingers...

Next day the quail cells look okay, with no sign of the proliferating yeasts. But now I have malice against the stuff.