Microbes or pathogens to be specific, are known to experience some unique low fluid shear forces in space that are quite similar in nature to those experienced within a live organism's body on earth. Research work funded by NASA has clearly revealed that the microbial virulence is enhanced when the bacterial cultures are provided an environment of microgravity.
It is well known that the ability of an organism to fight against the pathogens depends on its immune system i.e. whether it is strong enough to block their entrance into the body or kill them before they start infecting the body of the host or weak so that the pathogens would be easily able to enter and infect the body. Thus in brief, the ability of an immune system to defence against the invading pathogens gets changed. But after the recent ground breaking discovery by NASA, it has come into light that the ability of a bacteria to infect can get changed as well. To be clearer, a microbe's virulence can get altered during the course of microgravity.
Though a number of researches have been carried out till date concerning microgravity's impacts, no proper insight has been gained on genotypic and phenotypic responses of an organism to the microgravity during a space flight. Also, the impacts of microgravity on pathogens' virulence and the diseases associated with them has not yet been studied. Although, a study by Cheryl A. Nickerson at NASA shows that the microgravity conditions can cause the increase in a bacteria's ability to produce disease. Further, a study by J.W. Wilson et al. carried out at various major institutes including Kennedy space centre and Johnson Space Centre revealed that 167 transcripts and 73 proteins happened to change their expression with the conserved RNA-binding protein Hfq which is identified as a likely global regulator that is involved in the response to this environment. The involvement of Hfq was confirmed in ground-based microgravity model experiments. Also, the samples taken out on the space flights showed tremendous increase in the virulence ability of microbes. If strategies were to be designed to specifically target Hfq and other related regulators, the risks of infectious diseases during space flights could be greatly lowered and therapeutic and preventive measures on earth itself could be developed. For conducting this experiment, a culture of Salmonella typhimurium was grown on board of Space Shuttle Mission STS-115 and also on-ground. These cultures were later subjected to a close comparison for analysis.
Microbes in Space: On-Board of Space Shuttle
In September 2006 in a prior shuttle flight on Atlantis, Nickerson and her team showed that a gene's activation pattern happened to change in Salmonella typhi during the course of micro-gravity. They pointed out a remarkable altered expression in Salmonella colonies for 167 genes when they were compared to the same bacteria grown in identical conditions on Earth at normal gravity conditions. The colonies that were grown in space happened to produce illness nearly three times more likely when introduced into mice on ground.
Her team altogether showed that there is a master regulator switch for Salmonella's responses in microgravity during space flights. The cultures of Salmonella carried out in space exhibited a behaviour as if they were forming a bio-film which helps them in resisting attack by immune system or the antibiotic medicines. Though when the same culture was grown on ground they exhibited no bio-film production whatsoever. They noticed that the production patterns were changed for 73 proteins and the regulator for all this process during the course of microgravity was found to be Hfq which is a RNA-Binding protein. Nickerson quoted that this Hfq protein holds the key to therapeutic and preventive measures for microbial infections in astronauts.
After recent experiments on altered microbial virulence during microgravity, several parameters were changed in newer studies to study the impact of microgravity on a broader scale. The changed parameters included the concentration of ions and the charged salt particles present in body fluids. This was done in order to check if it had any controlling effect whatsoever on the increased infectivity or virulence of the pathogenic microbes in microgravity. Other studies also were conducted on various other microbes to test the gene activation patterns and virulence, especially on Streptococcus pneumoniae and Pseudomonas aeruginosa.
Microbes on Earth - Ground Experiments
While the experiments on bacterial cultures were being conducted in space, their control samples were being prepared and analysed on earth. After getting data from the shuttle experiments, both were compared to get a statistical view of analysis in order to get a better view at results. Tremendous alterations were observed in on-flight samples of Salmonella that has been already mentioned before.
The experiments on earth needing a microgravity environment, utilise the bio-reactors. Bioreactors come in different shapes and sizes depending on the type of experiment and they can be designed manually too, keeping in mind the requirements of the experiment. A bioreactor is basically a hollow cylinder which in this experiment, was filled up with culture media and cells. When the bioreactor rotates the cells experience the same condition of free fall as experienced in microgravity. The fluid that the cells grow in flows at a low speed past their cell surfaces that causes a low fluid shear force to be generated which is quite similar to the fluid environment that is experienced by the bacteria in the human body. The microbes send signals to their genes after sensing the flow of liquid past their surfaces resulting into production of certain proteins to suit to the environment in order to survive and proliferate. The bacteria cultivated on rotating bioreactor seemed to have enhanced its virulence or rate of infectivity given that the mice infected with these bacteria died three days earlier as compared to the control mice and large amount of bacterial colonies were found in the spleen and liver of these mice. Although the bioreactor can imitate only some aspects of microgravity, to obtain the full absence of gravity experiments on-board of space shuttle are a must.
Thus, it is well understood that the microbial virulence is enhanced to a great level in the microgravity environment. The low shear forces generated during the microgravity cause the gene activation pattern to change in the major microbes and thus enhanced infectivity levels are observed. These findings have led us to an insight into the mechanism of the disease causing Salmonella and preventive and therapeutic measures can be further developed in order to fight the diseases caused by the microbe. Studies have also provided the causes behind astronauts' illness during a space flight and the low level of immune system function. Apparently, the effect of these microbes on astronauts' health should not be under-rated as their infection might result into failure of the whole space shuttle experiment. Research from the past have provided us with the understanding of the elevated infective activity of microbes in microgravity. By studying the effect of infection by these pathogens in space, the results and findings could then be translated into better and safer therapeutic and preventive measures to keep us healthy on earth and astronauts on space in a microgravity environment.
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