Lucy M. McCully Espinosa, PhD

This project has been a blast! What’s up with these strange phages? What does all of this mean for plasmid conjugation? And what other overlooked treasures await to be found in this world of mobile genetics elements? Thank you for reading, and stay tuned for our next adventures.

Finally, we revisited the phages that depend on the F plasmid. We found members of all the known groups, and even a completely new, tailed(!) plasmid-dependent phage! @microMcCully here, introducing the wonderful FtMidnight, showing there’s even more diversity to be found! 13/

If they are so abundant, why haven’t we heard about them from metagenomic studies? Well, we think they’re just not getting through. They seem hard to recover even from samples where we know they are present at high abundance. 12/

These phages have zero accessory genome, and exactly the same gene content, but they can differ by a large number of SNPs. These ones, for example, only differ by ~500 SNPs, but they can have strikingly different host preferences! Look: 11/

There were so many, that we were worried about finding names for all of them, so we decided to go for “PRD” + a color name. We have some wonderful ones like PRDchartreuse, PRDaquamarine, and my favorite: PRDcerulean 😊. 10/

All the phages we were finding belong to the Tectiviridae family, and are closely related to PRD1. Not only were we finding them in large amounts but also, in more diversity than all the previously isolated phages of this group. 9/

Why? Well, because they had A LOT of plasmid-dependent phages. Like, in wastewater(!) there are almost as many plasmid-dependent phages as E. coli phages, and way more than S. enterica or P. putida phages (the hosts we were using in our assay.) 8/

So we started screening as many samples as we could, looking for phages that depend on IncP conjugative plasmids (like RP4). This is @implosian and me, showing off our samples. Our favorite samples: compost and wastewater. 7/

This sounds almost too easy to be true, but it works! Since the determinant of phage susceptibility can be horizontally transferred 🤯, many of these phages have a broad host range. If we add fluorescence to it, it’s even easier to see, and we get Phage DisCo! 🪩 6/

The species-specific phages will make plaques in only one of the two hosts, while the plasmid-dependent phages would be able to kill both because both strains are carrying the correct plasmid-encoded receptor. 5/

They are definitely an exotic bunch, and the thing is, we only know a few of them. We wanted to find more! So this was the plan: Let’s grow two different bacterial species in the same soft-agar lawn, both carrying the same plasmid. 4/