Attacked by Ooze!

Our listener letheasce followed through on a horrifically amazing dining scenario! The explanation:

Hi Chad and Chris,

I am the microbiologist who promised to have the podcast to be eaten in effigy by tiny amoebas. I did it! Here are the photos. 

Some background to explain what is happening in the photos: 

The “ooze” that I work with is the soil-dwelling slime mold Dictyostelium discoideum (Dicty to its friends). Dicty spends part of its lifecycle as a unicellular amoeba that preys on bacteria. When the amoebas reach high densities and there are not enough bacteria to eat, individual amoebas send chemical signals to one another and then come together to form a multicellular slug that travels towards light. The slug then stands up and transforms into a stalk that supports a mass of spores. The spores disperse and then hatch into more amoebas. It’s pretty cool! 

For the podcast to be eaten in effigy, I decided to use two bacteria to represent the podcast. I genetically engineered Klebsiella pneumoniae, a good food bacterium that we often feed to Dicty in the lab (cheaper than hogs or relatives!), to produce a green fluorescent protein (GFP). I also chose to include a strain of Paraburkholderia agricolaris that was genetically modified to produce a red fluorescent protein (RFP). Unlike Klebsiella, Paraburkholderia infects amoebas and isn’t consumed as food. One of the unique characteristics of Paraburkholderia is that it can alter the behavior of the infected amoebas, causing the amoebas to carry bacteria like Klebsiella that would otherwise be digested. Carried bacteria can be used to seed populations of prey bacteria at new sites. As a result, this behavior is sometimes called “farming” or, my favorite, “packing a lunch”. 

For this... project? fan art? ?? ... I mixed Dicty spores with the two bacteria. I used this mixture to paint "HP Podcraft" on a petri plate (which was kind of challenging, since the bacteria and spores can't actually be seen at this point). After one day, the GFP labeled bacteria had grown enough to clearly form letters. By the following day, the amoebas had hatched and started to eat the bacteria, resulting in clear spaces in some of the letters. By day 4, many of the amoebas aggregated to form slugs and started traveling towards the edges of the plate, which made the letters look fuzzy where moving slugs smeared the bacteria. Slugs infected by Paraburkholderia agricolaris leave a trail of bacteria behind them as they move and, by days 5-8, bacteria in the slug trails had grown enough to make the trails visible. The RFP labeled Paraburkholderia bacteria (which looks orange in the photos) took over most of the areas where the amoebas had eaten away the GFP labeled bacteria. There are also many Dicty fruiting bodies, which stand up from the plate. I probably could have gotten the amoebas to eat more of the letters if I hadn't included the Paraburkholderia, but then I wouldn't have gotten all those cool slug trails! 

I hope you have enjoyed being eaten in effigy by tiny amoebas. Thank you for the many years of wonderful podcasts! Please know that your work has contributed to the happiness and sanity of at least one amoeba-studying scientist. 

Best,

letheasce

NSF postdoctoral fellow, Washington University in St. Louis