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Unformatted text preview: all positively
charged proteins are synthesized. They bind to the DNA of the nucleoid condensing it
into a tightly packed, donut shaped structure. In addition to the nucleoid, the central core
(which is surrounded by the cell membrane) contains ribosomes. The central core is
essentially a highly dehydrated cytoplasm.
In the final act of sporulation, the cell wall of the mother cell (now called a sporangium)
is degraded by autolytic enzymes releasing the mature spore. FOOD-289 Endospore
properties Endospores are highly resistant to a variety of deleterious environmental conditions.
very resistant to toxic chemicals and highly acidic or basic conditions.
very resistant to the damaging effects of UV radiation and X-rays.
the most desiccation resistant biological structures known.
the most heat-resistant biological structures surviving boiling temperatures for hours. The radiation resistance of endospores is linked the small positively proteins complexed
the chromosome while their resistance to chemical permeation is linked to the properties
of the spore coat.
The heat and desiccation resistance of endospores is at least partly attributable to
their water content. The endospore is highly dehydrated, its cytosol consisting of only
about 15% w/v water by weight. This is little more than the water that is involved in
hydration shells around the various charged macromolecules, thus there is essentially no
free water present. In other words, the desiccation resistance of an endospore is due to
the fact that it is a structure whose essential nature is already a desiccated one. Heat
resistance is also linked to water content because dried proteins are more resistant to
heat denaturation that hydrated proteins.
It is interesting to note that although the endospore is resistant to a wide variety of
environmental insults, such as high temperature and ultraviolet radiation, these
conditions do not induce sporulation. Only nutrient deprivation is an effective trigger.
Thus it seems the purpose of sporulation is to place a protective coat around the cell’s
genome so it can survive starvation conditions.
With so little water, endospores exhibit little in the way of chemical or metabolic
activity (no respiration, no biosynthesis, no DNA replication, no transcription or
translation, no DNA repair, no motility, etc.). Because of their cryptobiotic nature
endospores are a dormant structure and very long lived. How long is not clear, but
there are certainly well-documented examples of endospores being able to germinate after
hundreds of years. The average age of an endospore in soil has been estimated to be 30
years but endospores may be able to live for a very long time; recently a spore
preserved in amber for 25-40 million years was reportedly revived. Endospore
germination. Once proper nutrient conditions arise, another genetic program, called germination, is
triggered (=environmentally regulated gene expression) to wake the dormant.cell.
Metabolic activity resumes and the endospore swells an...
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This note was uploaded on 10/25/2013 for the course MICB 201 taught by Professor Davidturner during the Fall '12 term at UBC.
- Fall '12