How does life begin and evolve? Does life exist elsewhere in the universe? What is the future of life on Earth and beyond?
These questions have lingered for many years, and we still do not fully know the answers to them. NASA, however, in its efforts to sustain life here on our home planet and chart a course for humans to explore the Moon, Mars, and beyond, is going to new depths to better address them – deep beneath the ocean surface.
In the floors of our oceans are holes that spew hot, gaseous, mineral-rich liquids from the deep, subsurface magma below. Scientists from NASA’s Advanced Life Support Group at Ames Research Center are hoping that these holes, called hydrothermal vents, may not only help them unlock the secrets of the deep, but help them learn if exotic life forms exist on other planetary bodies, including Mars and Jupiter’s moon Europa.
Because hydrothermal vents are thousands of meters underwater, they are not exposed to sunlight. Without sunlight, there may be abiotic life forms – life forms that exist devoid of photosynthetic input or decomposition of organic materials – in or near these vents. NASA scientists hypothesize that the deep subsurface of Earth could be home to organisms that exist solely on chemical energy that is generated from the off-gassing magma below the ocean floor. They further hope that this extreme underground environment could provide insight into whether similar life forms exist elsewhere in the universe, in environments that are far removed from the Sun and therefore also require other sources of energy. For example, scientists have targeted Europa because of its thick
ice crusts and the mounting evidence that points to there being an ice-covered ocean that could potentially harbor similar hydrothermal vents.
To test their hypothesis, the Advanced Life Support Group scientists have built a life-detection instrument called Medusa to collect, store, and analyze sample organisms from erupting hydrothermal vents. For the sample analyses, Medusa is equipped with a spectral-analysis chemical sensor that uses a process called flow cytometry to examine the natural glow of light, or fluorescence, emitted from any of the samples collected as ocean water flows through the instrument. When the scientists retrieve the samples, they inject a dye into them that interacts with the fluorescence and emits colors to reveal their chemical composition.
Medusa has already been deployed several times to study hydrothermal vents, and scientists will continue to send the instrument to the bottom of the ocean in an effort to validate their theory. NASA also plans to test the instrument in other extreme environments of Earth in its continuing quest to seek unknown life forms. Meanwhile, scientists are working to apply the spectral-analysis capabilities of Medusa’s chemical sensor to other areas of research, especially in studying the effects of gravity and cosmic radiation on human cells to possibly create an enhanced system for monitoring the biological effects of space travel on astronauts.
To develop the advanced flow cytometry process that is at the crux of Medusa and may one day be part of an advanced astronaut health-monitoring system, NASA sought the help of private industry. The Agency issued a solicitation through the Small Business Innovation Research (SBIR) program at Ames to find a partner for the project. Specifically, NASA needed a partner that could produce a high-speed flow cytometry process to continuously monitor cells for anomalies and bacteria growth. The system would ideally be able to image cells with high-fluorescence sensitivity and would be tolerant of wide variations in sample concentration and other characteristics by having a wide depth of field, allowing cells to be kept in focus regardless of where they happened to be in the flow stream.
Flow cytometry is a powerful technique, but it has several limitations that hinder its use for NASA projects. Most commercial flow cytometers cannot image cells like a microscope. Instead, they measure only the total amount of fluorescence emitted by each cell. Because they do not have the ability to determine where in the cell the signal is coming from, their applications in cell biology are mainly limited to measuring the total quantities of specific molecules in or on the cell. A few flow cytometry systems can produce images of cells in flow using transmitted light, but these systems lack the sensitivity necessary to image faint fluorescence.
Flow cytometers also generally require that cells flow through the center of a tightly focused laser beam, which can make them vulnerable to misalignment. Designs that are less sensitive to misalignment tend to sacrifice fluorescence sensitivity.
Many flow cytometry systems are also just too big and impractical for NASA’s purposes, especially since they incorporate pressurized fluid vessels that employ gravity and high pressure to drive the sample through the system.
Amnis Corporation, a Seattle-based biotechnology company, developed a technology called ImageStream for producing sensitive fluorescence images of cells in flow, and happened to be seeking ways to get whole cells into focus in order to increase the usefulness of its systems for research applications. The company had several ideas for how to achieve an extended depth of field, all of which required a level of funding that was just not in its budget. When Amnis heard about the SBIR solicitation, however, the realization came that it could be the perfect opportunity to reap the funding necessary to develop extended depth-of-field technology. The company responded to the SBIR solicitation and proposed to evaluate several methods of extending the depth of field for its ImageStream system, pick the best method, and implement it as an upgrade to its commercial products. This would allow users to view whole cells at the same time, rather than just one section of each cell.