A year of microbiology publications: npj Microgravity wrap-up
Here's a look at all of the microbiology-relevant content published in npj Microgravity over the past year:
Four-year bacterial monitoring in the International Space Station—Japanese Experiment Module “Kibo” with culture-independent approach
A four-year study that monitored bacteria aboard the International Space Station (ISS) has discovered multiple species, mostly of human origin, living aboard. The research, by Masao Nasu and colleagues from Osaka University and the Japan Aerospace Exploration Agency, will help space agencies assess risks to astronauts during long-term spaceflight. The team found multiple types of bacteria lived on the Japanese Experiment Module of the ISS, named Kibo, despite it being disinfected weekly. Most bacteria were of human origin (e.g. gut microbes), which were likely transferred by the astronauts. A small proportion of bacteria were of non-human origin, such as Legionella, which the authors speculate arrived on resupply materials. Since microgravity can affect bacteria in unpredictable ways, such as increasing their virulence, tracking bacterial habitation in the ISS will provide insights for future space travel.
Physiological fluid shear alters the virulence potential of invasive multidrug-resistant non-typhoidal Salmonella Typhimurium D23580 – Brief Communication
Behind the Paper: Investigating the physical force of fluid shear and how it drives pathogen responses and infectious disease outcomes – npj Microgravity Community post
By mimicking key aspects of the physical force environment that pathogens encounter during the infection process in the human body (like fluid shear), a team of scientists led by Cheryl Nickerson at the Arizona State University unveil new insights into the mechanisms of infectious disease not possible using traditional experimental conditions. Once inside the human body, infectious microbes like Salmonella face a fluid situation. The bacteria live in a watery world, surrounded by liquid continually flowing over and abrading their cell surfaces—a property known as fluid shear. The team explore the effects of physiological fluid shear on ST313—a particularly dangerous type of Salmonella resistant to multiple antibiotics—by using a “rotating wall vessel bioreactor” designed by NASA that simulates the low fluid shear environment encountered by cells during culture in the microgravity environment of spaceflight and also in areas of the human body.
Exposure of Mycobacterium marinum to low-shear modeled microgravity: effect on growth, the transcriptome and survival under stress
Microgravity alters gene expression in a pathogenic waterborne microbe — changes that could pose a health risk to astronauts in space. Lynn Harrison from the Louisiana State University Health Sciences Center in Shreveport, USA, and colleagues grew an infectious bacterium called Mycobacterium marinum, a close relative to the microbe responsible for tuberculosis, in a rotary cell culture system that causes the low fluid shear dynamics associated with microgravity. Bacteria in this state grew slower with different expression levels of several hundred genes compared to those cultured under normal gravity conditions. Some of these molecular differences are similar to those elicited when mycobacteria infect human cells, suggesting that space might make the microbes more pathogenic. However, microgravity also made the bacteria more sensitive to certain stressors like hydrogen peroxide, so the overall impact on virulence is still unclear.
Investigation of simulated microgravity effects on Streptococcus mutans physiology and global gene expression
The gene expression patterns, metabolism and physiology of tooth cavities-causing microbes change in a space-like gravity environment. These findings could help explain why astronauts are at a greater risk for dental diseases when in space. Kelly Rice and colleagues from the University of Florida, Gainesville, USA, cultured Streptococcus mutans bacteria under simulated microgravity and normal gravity conditions. The bacteria grown in microgravity were more susceptible to killing with hydrogen peroxide, tended to aggregate in more compact cellular structures, showed changes in their metabolite profile and expressed around 250 genes at levels that were either much higher or lower than normal gravity control cultures. These genes included many involved in carbohydrate metabolism, protein production and stress responses. The observed changes collectively suggest that space flight and microgravity could alter the cavities-causing potential of S. mutans.
Three-dimensional organotypic co-culture model of intestinal epithelial cells and macrophages to study Salmonella enterica colonization patterns
Using spaceflight analog bioreactor technology, Cheryl Nickerson at Arizona State University and collaborators developed and validated a new three-dimensional (3-D) intestinal co-culture model containing multiple differentiated epithelial cell types and phagocytic macrophages with antibacterial function to study infection by multiple pathovars of Salmonella. This study is the first to show that these pathovars (known to possess different host adaptations, antibiotic resistance profiles and disease phenotypes), display markedly different colonization and intracellular co-localization patterns using this physiologically relevant new 3-D intestinal co-culture model. This advanced model, that integrates a key immune cell type important for Salmonella infection, offers a powerful new tool in understanding enteric pathogenesis and may lead to unexpected pathogenesis mechanisms and therapeutic targets that have been previously unobserved or unappreciated using other intestinal cell culture models.
Long-duration spaceflight increases the reactivation of latent herpes viruses in astronauts and is accompanied by a rise in stress hormone levels. This study shows that the frequency and viral loads of reactivation of Epstein-Barr virus, varicella-zoster virus, and cytomegalovirus were even greater in blood, urine, and saliva samples from astronauts staying 60 to 180 days onboard the International Space Station than has previously been observed for short-duration (10–16 days) missions. Changes in viral reactivation were also found to be associated with changes in the daily trajectory of salivary cortisol during these long-duration missions. These results indicate that the effects of the microgravity environment on the immune system are increased with prolonged exposure and highlight the potential increased risk of infection among crewmembers.
Pyrocystis noctiluca represents an excellent bioassay for shear forces induced in ground-based microgravity simulators (clinostat and random positioning machine)
Earth-based laboratories can now assess the accuracy of tools used to simulate living organism growth and behaviour in space with bioluminescent assays. Researchers often use rotating machines to minimize gravity effects during the design of extra-terrestrial experiments with plants, cells, and small animals. Jens Hauslage from the DLR German Aerospace Center and colleagues report that device-specific shear forces produced during mechanical movements may cause misinterpretations of initial test data. They developed a biosensor based on marine plankton, known as dinoflagellates, which have cell membranes that naturally emit light when touched by predators. Calibrating this bioluminescence against mechanical stress helped determine the top-like, 2D rotations of ‘‘clinostat’’ devices provided microgravity-like conditions. However, the unexpected 3D movements of Random Positioning Machines generated enough shear force to impact studies of cell signaling pathways or metabolic reactions.
The adaptation of Escherichia coli cells grown in simulated microgravity for an extended period is both phenotypic and genomic
Bacteria grown for an extended period of time under simulated microgravity adopt growth advantages. George Fox and colleagues from the University of Houston, Texas, USA, cultured Escherichia coli bacteria for 1000 generations in a high aspect rotating vessel to simulate the low fluid shear microgravity environment encountered during spaceflight. They then performed growth competition assays and found that the 1000-generation adapted bacteria outcompeted control bacteria grown without simulated microgravity. Genomic sequencing of the adapted bacteria revealed 16 mutations, five of which altered protein sequences. These DNA changes likely explain the growth advantage of the bacteria grown for multiple generations in simulated microgravity. Similar adaptations during prolonged space missions could result in nastier pathogens that might threaten the health of astronauts. Fortunately, the microbes did not appear to acquire antibiotic resistance over the 1000 generation in the modeled microgravity culture.