Biological complexity: how stressed bacteria go dormant (Introduction)

by David Turell , Friday, November 11, 2016, 22:59 (2934 days ago) @ David Turell

Another layer of genetic controls is found to control the process of dormancy, as a way of surviving threatening stress such as loss of oxygen:

http://phys.org/news/2016-11-newly-genetic-code-bacterial-survival.html

"MIT researchers have now discovered another layer of control that helps cells to rapidly divert resources in emergency situations. Many bacteria, including strains that cause tuberculosis, use this strategy to enter a dormancy-like state that allows them to survive in hostile environments when deprived of oxygen or nutrients.

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"Dedon and colleagues have previously shown that stresses such as radiation or toxic chemicals provoke yeast cells to turn on a system that makes chemical modifications to transfer RNA (tRNA), which diverts the cells' protein-building machinery away from routine activities to emergency action.

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"Once a tRNA molecule is manufactured, it is altered with dozens of different chemical modifications. These modifications are believed to influence how tightly the tRNA anticodon binds to the mRNA codon at the ribosome.

"In this study, Dedon and colleagues found that certain tRNA modifications went up dramatically when the bacteria were deprived of oxygen and stopped growing.
One of these modifications was found on the ACG threonine anticodon, so the researchers analyzed the entire genome of Mycobacterium bovis in search of genes that contain high percentages of that ACG codon compared to the other threonine codons. They found that genes with high levels of ACG included a family known as the DosR regulon, which consists of 48 genes that are needed for a cells to stop growing and survive in a dormancy-like state. (my bold)

"'When oxygen is lacking, these bacterial cells begin churning out large quantities of the DosR regulon proteins, while production of proteins from genes containing one of the other codons for threonine drops. The DosR regulon proteins guide the cell into a dormancy-like state by shutting down cell metabolism and halting cell division.

"'The authors present an impressive example of the new, emerging deep biology of transfer RNAs, which translate the genetic code in all living organisms to create proteins," says Paul Schimmel, a professor of cell and molecular biology.

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"The researchers also showed that when they swapped different threonine codons into the genomic locations where ACG is usually found, the bacterial cells failed to enter a dormant state when oxygen levels were diminished. Because making this tRNA modification switch is critical to bacterial cells' ability to respond to stress, the enzymes responsible for this switch could make good targets for new antibiotics, Dedon says.

"Dedon suspects that other families of genes, such as those required to respond to starvation or to develop drug resistance, may be regulated in a similar way by other tRNA modifications.

"'It is really an alternative genetic code, in which any gene family that is required to change a cell phenotype is enriched with specific codons" that correspond to specific modified tRNAs, he says.'

Comment: this is another example of the many layers of the genome, showing how complex the genome really is. Further note the bolded area that described how many genes are needed to control this process of dormancy. Recognize that when this system developed in bacteria it required multiple genes, and strongly suggests it developed by saltation. The other takeaway is that when a new process is developed, just as when a new species develops, large families of cooperating genes must be developed simultaneously.