When Marlys Houck looks up from her basement laboratory next to a 1,800-acre wildlife park in San Diego, California, she sees a man in a uniform holding a blue insulated lunch bag filled with small pieces of eyes, trachea, feet and feathers.
“Oh,” he says softly. “Here are today’s examples.”
It is stated that the bag in question contained small pieces of soft tissue collected from animals that died of natural causes at the zoo. Modern-day examples include a leaf frog and a starling.
The man holding the bag is James Boggeln, a volunteer at the zoo, and he gives the bag to Houck, the curator of this laboratory known as the “Frozen Zoo”. He and his team will begin the process of turning these tissue fragments into a research and conservation bank for the future. They will place the tissue in vials where enzymes will digest them, then lab members will slowly incubate them for a month; They will grow large numbers of cells that can be frozen and eventually revived for future use.
The nearly 50-year-old Frozen Zoo houses the world’s oldest, largest and most diverse repository of living cell cultures; More than 11,000 specimens representing 1,300 different species and subspecies, including three extinct species and those very close to extinction.
Today, the Frozen Zoo is run by an all-female team of four who keep watch over a vast collection of hand-marked bottles with labels such as “giraffe,” “rhinoceros” and “armadillo,” all stored in huge circular tanks filled with water. liquid nitrogen. In a world suffering from climate and biodiversity crises, putting species on ice offers a way to be hopeful about the future.
The work done here has always been meaningful, but the accelerating extinction crisis has put increasing pressure on Houck and his team. It’s a race against time to get the samples into the Frozen Zoo before they disappear from the world outside the laboratory. The women who do these jobs see it as their duty to keep the future in place.
The work can be demanding; For example, samples from birds, mammals, amphibians, and fish all require different processes. But when the stakes are this high, Houck describes it with a kind of reverence.
He feels the pressure of the role; While his predecessor was in office, a mechanical failure had led to the loss of 300 samples, a year’s worth of work. That’s why his mind is focused on safely storing the frozen samples at the zoo, Houck says: “But then it’s combined with excitement and joy, because it’s an honor to be able to do that.”
‘Collect things for reasons you don’t yet understand’
The zoo was founded in 1972 by a German American pathologist named Kurt Benirschke; Kurt Benirschke began collecting animal skin samples in his laboratory at the University of California, San Diego, and a few years later moved it to the San Diego Zoo. There was no technology at the time to use it beyond basic chromosome research, but Benirschke often quoted American historian Daniel Boorstin: “You have to collect things for reasons you don’t yet understand.”
That quote still hangs on a poster in Frozen Zoo, where Houck pulls human-sized bottles that resemble giant silver thermoses from liquid nitrogen tanks. The tanks are pressurized at -320F; This temperature stops the cells from moving or changing, keeping them alive but suspending animation. After this temperature, cells can revive and continue living as if decades or even centuries had passed.
No two species are exactly the same, and some groups are more difficult to protect than others. Frozen Zoo started with mammals, then expanded to cryobanking birds, reptiles and amphibians. Houck says the success rate in mammals is close to 99%. “In amphibians, it’s been closer to 1% for a few years, and now I think we’re at 20 to 25%. The birds are quite high up.”
The racks in the nitrogen tanks each hold 100 vials, and each vial contains 1 to 3 million living cells. These cells—from a more endangered creature, such as a giraffe, a lemur, or a vaquita—hold potential solutions to a range of current and future problems.
Eventually the cells could be used to bring back completely extinct species; But this is not the main purpose. Instead, the material is often used to save existing struggling species. In 2020, Frozen Zoo used cryopreserved DNA to clone a black-footed ferret, the first endangered species cloned in the United States. Last year, frozen cells cryopreserved 42 years ago were used to clone two of Przewalski’s critically endangered wild horses, restoring valuable genetic diversity to the living population that would make it more resilient to new diseases or environmental threats. One of the foals was named Wolf, in memory of the Zoo’s founder.
The work by San Diego’s Frozen Zoo is part of a global movement to cryobank everything from animals to seeds. Today there are about a dozen wildlife-based cryobanks around the world, mostly located in North America and Europe.
We are losing species faster than science can keep up. The least we can do is try to bank this material
Sue Walker, Nature’s Safety
Sue Walker, chief scientific officer at Chester Zoo and co-founder and vice president of Nature’s Safe, a UK nonprofit cryobank that collects living cells, sperm and eggs, says the work done in San Diego is particularly groundbreaking. Within a few decades, it may be possible to transform these cells into pluripotent stem cells that can be reprogrammed to produce sperm and eggs, she says.
In an ideal world, species would be protected in the wild; but in reality this is not the case. “We are losing species faster than science can keep up,” he says. “So the least we can do is try to accumulate this material.”
Since it is difficult to obtain permission to bring tissue from animals in other countries, the hope is to increase cryobanking capacity locally elsewhere, particularly near conservation centers in Africa, South America and Southeast Asia. However, this means developing the capacity to process and maintain the cell population in a uniform manner. Walker says it’s expensive and complicated, but it’s also necessary.
“I think we need to put everything on the line to save some of these endangered species,” he says. “It’s about banking hope.”
Time machines to the past and future
Working on cell cultures can be like starting a time machine. Houck was once studying rhino chromosomes and opened a vial with his predecessor Arlene Kumamoto’s handwriting on it. Kumamoto had placed the cells in a deep freeze the month Houck graduated from high school. “I just thought, oh my God… he was freezing the cells I was now using for my work. “If he hadn’t done that, I wouldn’t be doing what I’m doing right now,” says Houck. “What are we doing today that will be used in the future?”
Julie Fronczek, who has worked at the zoo for 24 years, looks into her microscope to offer a theory as to why a group of women are leading this study at the Frozen Zoo. “We nourish the cells. They are living creatures and need to be fed and cared for, then you have to know what they want and when they want it,” she says. “Kind of like babies.”
The team adds about 250 to 350 species to the zoo each year. Houck says the leaf frog arriving today is a top priority. Is it a starling coming? Less critical. Such decisions weigh heavily on him. Since every new animal that arrives needs to be cultured and preserved, and takes up space in giant containers, one has to consider how many of those species are already represented and how many possibilities there are to get more of them. “I’d like to never have to turn anything down. “It would be better if we could accept every sample that comes in because they are all important.”
The collection includes three extinct species: the po’ouli, or Hawaiian honeycreeper, the Rabbs tree frog, and the Saudi gazelle. They hold their collective breath as they watch more species in their collection go extinct. “Next will probably be the white rhino and the vaquita,” says Houck.
The room where the tanks are located is full, but since the tanks are not yet at capacity, the team continues to work on culturing and preserving cells that could be a matter of life or death for endangered animals in the future.
In the future, the laboratory needs to update its methods; These handwritten bottles will eventually turn into scannable barcodes. At the same time, new scientists need to come and carefully observe the zoo growing on the ice.
“I think we’re all very protective of the frozen zoo and its legacy and Dr Benirschke’s legacy,” says Houck. “And hopefully we can raise a generation that will carry this forward.”