Cyanobacterial Sleeping Beauty
(October 27th, 2016) Our writer, Alejandrolvido, tells a scientific fairy tale, starring a perished prokaryote princess and several lion-hearted microbiologists, bringing it back from the dead.
Once upon a time in a lab far, far away, there was a cyanobacterial princess named Synechocystis sp. PCC 6803, whose beautiful green colour was the envy of several scientists from Germany, the Czech Republic and Japan. Conjuring postdocs and technicians, the scientists cast a spell over the greenish algae on a full moon night: “We shall take the nitrogen sources away from you, and your lustful pigments will be gone - you will suffer from chlorosis. Only an act of nutritional love can wake you from eternal sleep.”
Powerless, Synechocystis bore the deprivation of nitrogen and accumulated as much glycogen as possible, just to see how its photosynthetic pigments and thylakoid membranes faded away. A profound metabolic silence engulfed the dormant princess and all of the cyanobacterial kingdom. Ages passed, or to be more precise, one month. Then a PhD student named Alexander Klotz came to the lab of Karl Forchhammer and fell in love with Synechocystis. Daringly, he prepared medium containing precious nitrogen sources and, in an act of true love, inoculated the chlorotic princess into a fresh new world.
What happened hereafter was true mystical magic… and can be explained by science. Upon exposure to nitrogen, the scientists beheld the transcriptional programme of the awoken, using a high-density microarray with 8,916 transcripts. They found that 17.6% of the entire transcriptome was regulated during the process.
Yawning and stretching, Synechocystis, at first, induced the entire translational apparatus, from ribosomes to chaperones - an energy-consuming task supported by catabolising the stored glycogen through respiration. Transcripts for the production of the beautiful photosynthetic pigments and the components of the photosystem machinery followed. Mysteriously, transposases and CRISPR-associated transcripts also came along with the reinstallation of the photosynthetic capacity. After having used up most of the glycogen, and equipped with new pigments, transcripts for cell division finally appeared and Synechocystis was once again free to proliferate - only 48 hours after being kissed alive by the brave student Alexander and his nitrogen-rich medium.
Micrographs confirmed that indeed the starvation spell was broken, glycogen granules miraculously disappeared as the chlorotic cells slowly woke up. At the same time, the thylakoid membranes with the photosynthetic machinery were resynthesised. Consistently, measuring photosystem II’s fluorescence by Pulse-Amplitude-Modulation (PAM), our microbiological lab wizards showed that almost one day was required to have the photosynthetic machinery back in action, duly producing oxygen. The scientists also noticed that once cell division starts, the number of chromosomes per cell drops to five on average, which is remarkable because Synechocystis is usually polyploid with up to 20 chromosomes per cell. Did the cells degrade their extra chromosomes to get phosphate? The science men deliberated and came to the conclusion that it is far more likely that the rapid rate of cell division caused this decrease in chromosome number.
The fairy tale of the dormant microorganism occurs all the time and everywhere on our planet. Understanding its narrative will greatly improve our knowledge of how cells survive starvation. Many of the pathogens we struggle with, such as Mycobacterium tuberculosis, have similar stories of quiescence, but with less of a happy ending for humans. In the case of princess Synechocystis, however, the fairy tale ends with a Cell paper that provides the first insights into the resuscitation of a dormant cyanobacterium from chlorosis. And everybody lived happily ever after… until the next experiment.
Picture: Sleeping Beauty by Jennie Harbour