21 October, 1996
Subject: Re: Journal 21 October 1996
Live from the Polar Duke in the Gerlache Strait
Location: 64.13S X 61.51W Wind Speed: 0.6 m/sec
Boat Speed: 0.0 knots Wind Direction: 139.8 degrees
Boat Heading: 131 degrees Barometer: 985.4 mb
Humidity: 81 % Air Temp.: -0.6 C
Salinity: 33.7 0/00 Water Temp.: -1.3 C
General Weather Conditions: Delightful outside, feels warmer. Some cloud coverage and flurries later in the day.
The ice has moved into the Gerlache Strait. This happens when there are sustained winds in our general direction. The pack ice that has broken up is pushed into narrow opening and up against the sides of islands or the penninsula. Sometimes it's gone by the next day and at other times it stays with us for longer periods of time.
Today was so long that I don't know where it stated and ended and tomorrow begins our last diel. The in situ incubation boxes were deployed along with a production experiment. Up on the helo deck all of the large incubation boxes were filled. I also have started helping one of the graduate students (Melissa from Oklahoma State University) with an experiment that she has just started.
Melissa's experiment, as well as many of the other experiments that we are doing, is designed to investigate damage and repair in bacteria. It is essental to have a basic understanding of these concepts to understand the research we are doing in Antarctica.
When specific wavelengths of radiation are absorbed by cells the energy is dissipated via photochemical reactions. Wavelengths of radiation, for example UVB radiation, contain energy, when this energy strikes and is absorbed by cells it causes reactions to occur. Photochemical simply means that a chemical reaction takes place and this reaction is light dependant. The products of these chemical reactions are called photoproducts.
UVB wavelengths are responsible for most damage to organisms by sunlight. The UVB wavelengths produce lesions, or cuts that lead to single-strand and double stramd breaks in DNA molecules. DNA molecules are responsible for cell replication and synthesis of proteins. Proteins are used to repair cells and other cellular functions. DNA damage is often lethal to the cell or the damage may be duplicated (cancerous cell are a good example of replication of mutant or damaged cells). Other damage that results from the lesions include direct DNA damage in the form of cyclobutane dimers, which are major distortions in the DNA double helix. These breaks or lesions (dimers) in the DNA can be measured. Obviously the greater the number of dimers, the greater the damage from UV radiation.
UVR imposes chronic stress on marine bacteria by supressing bacterial production and proliferation and photochemically destroying bacterial enzymes. On low ozone days, when high levels are UVB radiation are detected, bacteria will be damaged. As the cells are damaged, repair mechanisms are triggered. If the cells are expending energy for repair, they aren't dividing, growing or metabolising food, so production falls.
Cellular defenses against UV radiation varies among organisms. Some produce chemical compounds that absorb UV radiation energy and provide direct protection from UV radiation. Organisms may use several different mechanisms of DNA repair to reverse damage from UV radiation.
The two bacterial repair mechanisms that are important to this study include, a process called photoreactivation and nucleotide excision repair. These repair processes are measureable.
Photoreactivation utilizes the enzyme photolyase and visable light to reverse damage. Light must be present for this repair to take
place. The enzyme photolyase is extractable and may be quantified. If the amounts of photolyase is high, it means that there is alot of repair taking place which must mean that there is a great deal of damage.
Nucleotide excision repair is a little more complicated. This is a system that excises the damaged bases. The bases are the rungs of the twisted ladder or double helix, of the stands of DNA. The order of the bases is extremely important, the bases are the code that tells the amino acids the order to line up in order to synthesize proteins. This system also resynthesizes DNA in the damaged area and ligates nicked strands. Bacteria regulate this repair of UVR damage to DNA (nucleic acids) through the induction of a series of approximately 20 genes. This is called the 'SOS' network. Central to the functioning of this network is the recA gene. The functioning of this repair network is not light dependent.
The recA gene provides the code for the RecA protein. This protein is used in the repair process. The mRNA (messenger RNA) carries the code for the synthesis of the RecA protein. This is what we are interested in measuring, the mRNA recA. The recA gene is always present in bacteria regardless of whether the bacterial cell is being damaged or not. It is only when the recA gene is making RecA protein that damage is being repaired. We aren't interested in measuring the amount of protein being produced because it is being used up for repair. By measuring the mRNA recA we can get a good indication of the extent of damage repair.
Both RECa and photolyase will be extracted from bacteria that we are collecting day after day on filters. This will be done at labs back in the states. All we are doing onboard ship is collecting sample of water and running it through 0.8 and 0.2 micron filters to concentrate bacteria. The samples are frozen ar -80 F to keep them from degrading.
However, we are varying the times and conditions of the water collection.
Next time I will explain some of the experiments that we are doing.
NSF Teacher in Antarctica
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