The Dragon capsule’s release from the space station in March was delayed by a day due to rough seas in the area planned for the splashdown, otherwise the release and splashdown went exactly as planned. If you are curious about seeing how Dragon leaves the ISS, here is a time-lapse video showing the process. It is pretty amazing when you remember this is all going on at 5 miles per second, 250 miles above our heads.
Following splashdown in the Pacific, the Dragon capsule was loaded onto a ship and transported to California. While en route, Dragon’s cargo was unloaded from the capsule and our samples along with other payload items were placed into a large container. This container was first removed from the docked ship, then the empty Dragon capsule was covered with a tarp and lifted off the boat. The exterior surface of the capsule looks pretty beat-up from the heat of re-entry, however the payload that is visible in the video looks pristine. The Dragon worked flawlessly for the return trip!
After being unloaded from SpaceX’s Dragon capsule, our space-grown fixed seedlings were returned frozen to Kennedy Space Center. I met with NASA specialists at the SSPF (Space Station Processing Facility) to remove our experiment from the space hardware. Our BRICs – the aluminum shoebox-sized containers holding our samples in their PDFUs (Petri Dish Fixation Units) had been placed in the fridge for a day in order to defrost so that the containers could be easily disassembled. The NASA team and myself gathered in the lab first thing in the morning to see how our seedlings fared while they were in space. This was the moment we’ve been waiting for! NASA hardware experts Susan and Michelle worked together to carefully take apart the BRIC container and then to open the PDFUs containing our samples. NASA quality control expert Jennifer observed the process, clipboard and camera in hand to document each step.
As the first PDFU was opened, we all leaned into the sterile hood to see the result: Success! Initial observation of our wild-type Arabidopsis plants was superb: Inside the petri dish sitting in fixative were dozens of seedlings, just as we hoped they would be. The next petri dish was identical. Fantastic! However, upon opening the third PDFU, things became more complicated. This was a PDFU with some of our mutant seedlings in it. These plants had also grown well, however, there were a couple of contaminating microbial colonies about the diameter of a pea that were growing with the seedlings, definitely not what we wanted to see.
We unpacked the rest of the space flight PDFUs and then moved on to the Earth-grown control petri plates. These samples are every bit as important as the space grown ones because it is vital to compare parallel samples grown on Earth. Given the contamination in the space-grown mutant we expected the same for the Earth-grown controls because we used the same batch of seeds and sample preparation protocols. However, all the Earth-grown petri plates (wild type and mutant) were pristine and filled with dozens of seedlings. Germination was excellent, the seedlings were well preserved, and there was plenty of plant material for analysis of gene expression.
Of course we are now working hard to define exactly how that contamination crept in to a few of our flight samples. Brian Hudelson, Director of the University of Wisconsin Plant Disease Diagnostics Clinic, very kindly identified it for us and no, nothing exotic or exciting, just regular old Penicillium, probably the most common contaminant found in experiments performed anywhere on Earth. We are now chasing down leads on how a few fungal spores may have slipped in as we assembled some of our sample dishes. Solving these kinds of technical problems is just part and parcel of doing business in space and is how we get better and better at designing for our next flight experiment – and yes, the Gilroy lab is going back to the ISS for another experiment! More about this in a future post.
Fortunately, all of our wild type samples (both space grown and Earth grown controls) were perfect. These are the critical samples for our analysis of gene expression and thus we will be able to answer most of the questions we set out to address with this experiment. Won-Gyu has already measured the seedlings, separated root and shoot, and isolated high-quality RNA from both samples grown in microgravity and grown on the Earth. The next step will be to quantify the changes in the expression of specific genes, in particular we are interested in what changes there might be in the expression of genes known to be regulated by low oxygen. Then using RNAseq, we will look at the shifts in the expression of all genes in the Arabidopsis genome. This technique will allow us to see what patterns of changes occur in all expressed genes and enable the discovery of other key genes that plants rely on as they adapt to growth in microgravity.