lecture14 - 20.106J Systems Microbiology Lecture 14 Prof....

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20.106J – Systems Microbiology Lecture 14 Prof. DeLong ¾ The plan for today: o The global nitrogen cycle o N 2 fixation – general considerations o Plant microbial symbioses – Rhizobium, Agrobacterium ± Key processes and prokaryotes in the nitrogen cycle o Organisms that reduce nitrate and nitrite instead of oxygen o Nitrogen fixation ± This is how new nitrogen gets into the atmosphere ± There are a lot of organisms that are capable of this ± It takes a lot of energy o All of these processes are mostly bacterial – if you took away the bugs, the nitrogen cycle wouldn’t turn o Cation exchange in the soil ± We dump urea and nitrogen in the soil – this eventually causes greater nitrogen loss o Forest soils versus cut soils ± In the forest soil, more recycling goes on ± In a clearcut forest, the ammonia stops getting taken up by the system ± With lots of ammonia but no plants to take it up, the bacteria eats it all up, and the soil loses nitrogen o In aquaria, nitrifiers are essential – the fish couldn’t stay alive otherwise o What happens when you dump lots of phosphate in a lake? ± You get big blooms of nitrogen-fixing cyanobacteria ± This is why phosphates aren’t around in detergents anymore – they’re a bit problem ± Phosphate is almost the only other thing that these bacteria need to grow, so they really take off – this leads to pollution problems – these bacteria create a lot of toxins ± You decrease the nitrogen to phosphate ratio o There are other organisms that can fix nitrogen – autotrophs, some archea, some proteobacteria o Energetics – you have to burn about 16 ATP for each nitrogen that gets reduced – you have to be producing a lot of energy
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This note was uploaded on 11/11/2011 for the course BIO 20.010j taught by Professor Lindagriffith during the Spring '06 term at MIT.

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lecture14 - 20.106J Systems Microbiology Lecture 14 Prof....

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