The mutant they focused on produces enough GTA that culture supernatants transfers any one chromosomal marker to about 0.0001 to 0.001 of the cells in a recipient culture. As each particle contains about 0.001 of the donor chromosome, and recombination of such short fragments is relatively inefficient, this means that the supernatant probably contains about as many particles as there are cells in the recipient culture. That was probably about 10^9 per ml.
The mutant grew poorly, and the authors interpreted this as a consequence of increased cell lysis associated with the increased GTA production. They maintained the strain by growing it in medium they had found to inhibit GTA production (PYE medium), and transfered it to a GTA-inducing medium (RCV) when they wanted GTA. After this transfer they observed that after several cell divisions about 10-20% of the cells died at the same time that high levels of GTA became detectable in the medium.
This is a very provocative result (too bad they don't show any data), because it implies that GTA production is very deleterious . I'd never heard of either medium; I wanted to find out what's in them but one of the disadvantages of reading old papers is that they and their references are often not available online. But simply Googling "PYE RCV" led me to the recipes - apparently they're quite widely used. PYE is just 0.3% peptone and 0.3% yeast extract, which makes it a slightly more dilute version of our old favourite rich medium LB. RCV is a defined medium used for R. capsulatus photosynthetic growth; it contains 0.4% malic acid as the only carbon source, 0.1% ammonium sulfate, thiamine, and other salts specified in papers that Springer will show me for $32.
So cells make lots of GTA in rich medium but not in the very poor medium used for photosynthetic growth. Hmmm...
But searching for the paper with the recipes for these media led me to an even older paper that I need to first read. This is Marrs 1974, PNAS 71:971-973, and PNAS is on line all the way back to the beginning. So I'll take a break to read this paper, and post on it before continuing.