Several genes were differentially expressed when exposed to microgravity as compared to normal gravity

With humans planning to colonise moon and other planets in future, scientists have been trying to understand and monitor the effect of microgravity or zero gravity from organism to molecular levels for developing strategies to ensure their survival in hostile environments.

Since gravity is necessary for all life forms, they undergo various physiological changes when exposed to microgravity. For instance, it has been known that microgravity, among others, causes osteoporosis, atrophy of muscles, immune dysfunction, sleep disturbances, cardiovascular de-conditioning, decreases rate of photosynthesis, alters bacteria’s pathogenesis and differentially regulates cells involved in growth and metabolism.

As part of understanding how microbes, known to adapt and thrive in extreme environments, survive in such conditions, scientists from CSIR-Centre for Cellular and Molecular Biology (CCMB) studied the effects of simulated microgravity on E. coli, the gut bacterium that was grown on special medium and supplemented with glycerol. Former director-grade scientist at CCMB, S. Shivaji is the lead author of the study, which was recently published in PLoS ONE.

Kotakonda Arunasri, Mohammed Adil, Katari Venu Charan, Chatterjee Suvro and Seerapu Himabindu Reddy are the other members of the study which was funded by the Indian Space Research Organisation (ISRO).

The results of the study showed that E. coli exhibited enhanced growth rate and that several genes were differentially expressed when exposed to microgravity as compared to normal gravity. While the results were in accordance with previous studies, the genes that were differentially expressed were not identical.

Dr. Shivaji said they looked at all the genes present in four different strains of E. coli.  As many as 20,336 genes were studied and it was found that initial exposure to simulated microgravity stimulated growth in laboratory strain of E. coli. When they examined the expression of genes, they noticed that a total of 100 genes were differentially expressed (either increased or decreased in function compared to normal gravity).

Unlike in the previous studies, it was found that none of the stress-inducible genes were up-regulated implying that the enhanced growth was due to adequate energy required for growth and DNA replication. He said the previous studies did not have glycerol as the medium and the genes that were up-regulated were stressed. In the present study, glycerol was the energy source and helped in overcoming the stress.

The implication was that any biological system when in zero gravity conditions in space should look for alternative sources from which it could derive energy.

Dr. Shivaji and his colleagues have taken up further studies using proteomic approach to unravel the role of candidate proteins in overcoming stress due to microgravity.

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