Mysteries of infection charted in spacebound worm

Mysteries of infection charted in spacebound worm

January 15, 2015

January 15, 2015

On Saturday, Jan. 10, 2015, SpaceX’s Falcon 9 rocket and Dragon spacecraft streaked skyward from Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida. Lacking human crewmembers, the vessel nevertheless carries very special living cargo—the tiny nematode worm, C. elegans and the foodborne pathogen Salmonella. 

In a first-of-its-kind experiment, the soil-dwelling creature will be used to examine the process of bacterial infection by Salmonella, in a reduced gravity environment. The study will be conducted in real-time aboard the International Space Station, which Dragon reached Monday morning. 

Cheryl Nickerson, Ph.D., a microbiologist at Arizona State University’s Biodesign Institute, and professor in the School of Life Sciences, designed the pathbreaking experiments. 

“Micro-5 is one of the most complex and challenging biological experiments ever performed during spaceflight,” Nickerson says. “It will be the first experiment to profile the entire infection process of a living organism in real-time in microgravity to measure disease-causing potential (virulence); the first to examine the host-pathogen interaction at the cellular, molecular, and immune response levels in a whole animal; and the first to evaluate the use of a nutritional countermeasure to protect against infection.” 

Nickerson emphasizes the enthusiasm and perseverance of her research team as central to the mission: “This study has been five years in the making and would not have been possible without the dedication and hard work of my lab members Jennifer Barrila (a co-investigator on the project), Rebecca Forsyth, Richard Davis and graduate student Jiseon Yang. Both Jennifer and Rebecca led the effort in experimental optimization and implementation.”

The project is known as NASA Micro-5, but has been appropriately dubbed PHOENIX, (Pathogen-HOst ENteric Interactions EXperiment), by the Nickerson team members. 

Under microgravity aboard the ISS, the tiny C. elegans worm will undergo infection by Salmonella, with state-of-the-art tools beaming live images and data of the entire process to Nickerson’s ground-based crew. Other portions of the experiment will be preserved for subsequent molecular genetic and microscopic analysis upon landing.

The findings are of profound consequence for astronauts on space missions, who may fall victim to such intensified invaders. As Nickerson notes, the combination of heightened bacterial virulence and suppressed immune response in crewmembers (induced by the rigors of spaceflight), is a dangerous one. 

Removing the variable of gravity in order to uncover the subtle interplay of host and pathogen will help advance strategies to protect crewmembers in flight. It will also benefit scientists and clinicians developing improved therapeutics to combat Salmonella and other infectious agents on earth by unveiling novel mechanisms that are important for the infection process. 

The Micro-5 mission builds on extensive prior research by Nickerson’s team, which demonstrated that infectious pathogens of human importance, like Salmonella, modify their molecular, genetic and pathogenic behavior under microgravity, accentuating their virulence. 

 

An aggressive intruder

The rod-shaped Salmonella bacterium is the leading source of foodborne illness-causing hospitalization and death in the United States. (According to the Center for Disease Control, Salmonella is responsible for close to 20,000 hospitalizations and nearly 400 fatalities annually in the United States alone.) 

In earlier experiments, Salmonella cultured under low gravity conditions in space were returned to earth, where they were used in animal infection studies where they exhibited a unique increase in virulence and novel changes in gene expression. (In a follow-up spaceflight study to determine how well the animal infection studies mimicked what might happen in humans, the team infected human intestinal cells with Salmonella during spaceflight.)

In a significant advance, the Micro-5 project tracks the entire infection process for the first time in a living organism in the microgravity environment, yielding more precise and accurate results, far removed from the effects of earth’s gravity.

Nickerson and her colleagues have learned that the amplified virulence elicited by low gravity stimulates profound alterations in Salmonella gene expression. Curiously, however, the pattern of regulated genes observed under spaceflight conditions is distinct from that observed when virulence genes are activated in Salmonella grown on earth. 

Nickerson’s team also identified a master control switch in charge of modifying Salmonella genes under spaceflight conditions—a protein dubbed Hfq. This regulatory protein is observed in a broad range of life forms, including the model organism C. elegans, used in the present study. Her team discovered that other microbes also use Hfq to regulate their spaceflight responses – making this protein the first spaceflight-induced regulator that acts across bacterial species. This suggests that bacterial cells are evolutionarily hardwired to respond to microgravity in unique ways. 

Finally, the team’s previous spaceflight research offered tantalizing hints as to how Salmonella’s spaceflight-induced virulence might be outwitted. Such virulence appears to be regulated in part by ion/salt concentrations present in the bacterium’s growth environment. The group was able to turn off the spaceflight-induced increase in virulence by modulating the ion concentration in which the bacteria were grown. Results indicate that one salt in particular—phosphate—potentially holds the key to counteracting Salmonella lethality. 

Micro-5 will explore phosphate as a nutritional countermeasure to shut down Salmonella’s invasive, disease-causing potential, thereby protecting C. elegans. Success of this approach could have implications for better shielding crewmembers from infection as well as developing innovative strategies for combating Salmonella infections on earth. Hence, the current mission draws together the various threads of the host-infection process elucidated in Nickerson’s earlier research.

 

The worm that keeps on giving

The nematode worm C. elegans, first observed around 1900, is a translucent creature measuring just 1 mm in length. It typically lives in temperate soil environments. The nematode has been among the most important model organisms used in wide-ranging biological and biomedical research. Because it has an intestinal tract remarkably similar to humans, and an innate immune system, it is ideal for studying the process of infection by microbial invaders like Salmonella. 

C. elegans was the first multicellular organism to have its entire genome sequenced. Remarkably, the worms share roughly half of their genes with humans, making them an attractive human surrogate for many types of research. The hearty organism can actually be frozen and thawed for later experimental use and they have already proven their resilience aboard prior spaceflight missions. 

 

Aboard the space station, a new automated camera system designed by the company BioServe specifically for this experiment will provide real-time on-orbit video results throughout the infection process to the Nickerson team at ASU, capturing the behavior of infected nematodes in space. 

The videos will be used in a joint STEM educational outreach with Orion’s Quest, allowing high school students to help Nickerson’s team count the nematodes surviving infection in spaceflight as compared to identical synchronous ground controls. The team will then be able to study the survival curve of infected nematodes, juxtaposing the results with identical earthbound experiments. 

The experiments to profile molecular genetic responses in both the host and pathogen during infection, as well as microscopic imaging of the infected nematodes will be performed in the Nickerson lab upon landing.

 

The power of weightlessness

As Nickerson notes, observing microbial behavior under extreme conditions including temperature, pressure, and pH, has been a fertile terrain for biological discovery. The reduced gravity condition present aboard the ISS (known as microgravity) is the latest extreme environment to be explored, providing a new tool to investigate the influence of various forces on life that are often obscured on Earth by the presence of gravity.  Researchers hope to better understand how these forces are manifest in the structure and function of cells, helping to dictate whether they behave normally or transition to disease. 

Teasing out the effects of these forces in cells, tissues and organs promise to yield rich dividends for global human health, providing new insights into infectious disease, cancer, aging, bone, and muscle wasting diseases, as well as paving the way for advances in tissue engineering. 

 

Infectious diseases alone are responsible for 35 percent of global fatalities and remain the world’s leading killer of children and young adults. The economic impact on the U.S. exceeds $120 billion annually. New treatments and methods of prevention are vitally needed and space may be one of the frontiers in which to find them.

In addition to Cheryl Nickerson, Ph.D., the Micro-5 team includes researchers in her lab at the Biodesign Institute at Arizona State University; Dr. John Alverdy at the University of Chicago Medical Center; Dr. Mark Ott at the NASA Johnson Space Center; the flight hardware team at Bioserve; their NASA support and management teams at Ames and KSC; and astronauts aboard the ISS who will perform the experiments aboard the ISS, and Orion’s Quest, a not for profit company dedicated to helping teachers connect their students with the space-based research of world-class scientists.

The rapidly developing field of microgravity research will be highlighted in a new open-access journal from Nature Publishing Group: npj Microgravity. Professor Nickerson will be the Editor-In-Chief of the new publication, whose inaugural issue is due out in two months. 

 

Written by: Richard Harth

Science Writer: Biodesign Institute

 

richard.harth@asu.edu