Transcript Nitrogen cycling

15
Microbes and Agriculture
No Microbes, No Hamburgers
Microbes on the Farm
• Connecting the nitrogen dots
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Recycling of carbon, oxygen, and nitrogen in soil and water
Carbon and oxygen cycled by plants, animals, and microbes
Nitrogen cycling done by microbes alone
The nitrogen cycle
• Nitrogen is essential element in many organic compounds
– Amino acids/proteins
– Nucleic acids
– 9% to 15% of dry weight of typical cell
• Estimated that 200 million tons of nitrogenous compounds created per
year by microbes
– Nitrogen fixation
• Free-living microbes
• Symbiotic microbes
농장에 존재하는 미생물
Microbes on the Farm
• Connecting the nitrogen dots
– Free-living nitrogen-fixers
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Azobacter
Beijerinckia
Clostridium
Nostoc (cyanobacterium)
Anabaena (cyanobacterium)
Manufacture ammonia from N2 in atmosphere
Conversion of ammonia into amino acids and proteins
As bacteria die, they are decomposed
Nitrogen-containing contents recycled for other organisms
Microbes on the Farm
• Connecting the nitrogen dots
Fig. 15.1: A) Nodules containing nitrogenfixing bacteria on the roots of a cowpea, a
legume plant; B) A false-color SEM of a
Rhizobium species comprising a root nodule
(Bar = 10 μm)
© Medical-on-line/Alamy Images
• Rhyzobium
• Bradyrhizobium
• Live in nodules on roots of legumes
– Soybeans
– Alfalfa
– Peas(완두콩)
– Clover
– Beans(강낭콩)
• Formation of bacteroids
Courtesy of Harold Evans
– Symbiotic nitrogen-fixers
Microbes on the Farm
• Connecting the nitrogen dots
– Bacteroids(박테로이드; 뿌리혹박테리아)
• Must live symbiotically, not independently
• No artificial nitrogen fertilizer required in fields with bacteroids
• High nitrogen content provided by bacteroids reaches humans
– Microbes to plants
– Plants to herbivores(초식동물)
– Herbivores to people
– Nitrification(질화작용)
• Nitrosomonas converts ammonia to nitrite ions
• Nitrobacter converts nitrite ions to nitrate ions
Plants use these nitrate ions
• Occurs under aerobic conditions
• Used as energy source by bacteria
Microbes on the Farm
• Connecting the nitrogen dots
– Denitrification(탈질화작용)
• Bacterial breakdown of nitrites to N2
– Biotechnology
• Trying to bring genes for nitrogen fixation from Rhizobium to
Agrobacterium tumefaciens, a bacterium that infects many different
plants
• Trying to engineer Rhizobium to live symbiotically with other
agriculturally important crops
Microbes on the Farm
• Those remarkable ruminants
– Ruminants(반추동물)
• Cud-chewers
– Cattle
– Sheep
– Deer
– Goats
– Camels
– Buffalo
• Diet of plants, grasses, high-carbohydrate plants
• Still produce proteins
• Consumed in human diet for meat
Microbes on the Farm
• Those remarkable ruminants
– Cellulase, to break down plant cell walls, provided by microbes in
rumen
– Cellulose broken down to glucose
– Glucose fermented by anaerobic microbes to other molecules
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Propionic acid
Acetic acid
CO2
Methane
– High energy content of material used to fuel microbial reproduction
• Rumen may contain 1012 microbes per milliliter
• Microbes plus undigested plant material passes to reticulum(제2위)
• Mixture is called cud
Microbes on the Farm
• Those remarkable ruminants
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Cud regurgitated
Rechewed and remixed with saliva
Reswallowed to rumen to continue fermentation and breakdown
Cud finally passes to omasum(제3위) and the abomasum(제4위)
• Proteases release amino acids from proteins
• Nutrients absorbed from intestines
주목할 만한 반추동물
Microbes on the Farm
• Those remarkable ruminants
– Non-ruminant herbivores(되새김 하지않는 초식동물)
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Horses
Rabbits
Guinea pigs
Still eat grasses, like ruminants
Cecum(맹장) contains microbes that perform same tasks as those in
rumen
– Coprophagous herbivores
• Reconsume fecal pellets
• Gives second pass through intestine to capture maximum nutrients
– Silage
Microbes on the Farm
• At the dairy plant(낙농 공장에서)
– Milk
• Ideal medium for culturing microbes
• Contents
– Water
– Casein
– Lactose
– Fats
– Vitamins
– Minerals
• Natural bacteria ferment lactose and produce lactic acid in
unpasteurized milk
– Souring
– Curdling
– Odor
Microbes on the Farm
• At the dairy plant
– Buttermilk
• Lactobacillus bulgaricus added to skim milk
– Fermentation and production of lactic acid
• Leuconostoc citrovorum also added to this milk
– Synthesis of polysaccharides to thicken milk
– Sour cream
• Made in same fashion
• Uses cream instead of skim milk
– Yogurt
• Concentrated milk
• Streptococcus thermophilus and Lactobacillus bifidus added
– Ferment lactose
– Produce acid
Microbes on the Farm
• At the dairy plant
– Acidophilus milk
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Pasteurized milk
L. acidophilus added
Bacteria colonize intestines
L. acidophilus crowd out harmful microbes
– Kefir
• Lactobacilli, streptococci, and Saccharomyces kefir
– Butter
Fig. 15.5
Fermented Milk
Products
© Photos.com
© melissa bouyounan/ShutterStock, Inc.
• Streptococci and Leuconostoc added to sweet cream
Microbes on the Farm
• Of curds and whey
– Cheese
• Produced from casein
• Three steps
– Curd formation
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Acid produced by bacteria
Forces casein to curdle
Formation of sour curd
Addition of renin, instead of acid, results in sweet curd
Leftover fluid is whey
Unripened curds make cottage cheese or cream cheese
– Curd treatment
– Curd ripening
Microbes on the Farm
• Of curds and whey(커드와
유청)
– Cheese
• Third step
– Curd ripening and resultant
cheeses
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Camembert
Cheddar
Pecorino Romano
Limburger(벨기에산 치즈)
Roquefort
Gorgonzola
Danablue
Blue cheese
Figure 15.6: Various cheeses
produced by microbes
Biotechnology on the Farm
• Genetic engineering in plants and animals
• Novel uses of plants
– Plantibodies
• Increased productivity of crops
• Enhanced fruits and vegetables
– Potatoes that don’t discolor when peeled
– Tomatoes that have longer shelf lives
Biotechnology on the Farm
• DNA into plant cells
– Development of callus from single plant cell in culture
– Eventually grows into mature, transgenic plant
– Methods of introduction
• Microinjection
• Biolistic injector
• Agrobacterium tumefaciens Ti plasmid
– Permanent integration into plant cell chromosome
– Generates crown gall
Biotechnology on the Farm
Fig. 15.7
Agrobacterium
tumefaciens induces
tumors in plants and
causes a disease
called crown gall. The
catalyst for infection
is a Ti plasmid
carrying DNA.
농업에서 생물공학
Biotechnology on the Farm
• Bacterial insecticides
– Bacillus thuringiensis (Bt)
• Kills moth larvae (and those of other lepidopterans)
specifically
• Harmless to plants and most animals
• Bacilli induced to form spores
• Spores harvested and dried, then sprayed on crops
(Dipel)
• More powerful strain, B. thuringiensis israelensis
Reprinted with permission from the American
Society for Microbiology (López-Meza, J.E. and
Ibarra, J.E.; Appl. Environ. Microbiol, 1996 April;
62(4): 1306-1310) Photo courtesy of Doctor J.E.
López-Meza.
Reprinted with permission from the American Society for Microbiology (López-Meza, J.E.
and Ibarra, J.E.; Appl. Environ. Microbiol, 1996 April; 62(4): 1306-1310) Photo courtesy
of Doctor J.E. López-Meza.
Fig. 15.8 B.
thuringiensis
Reprinted with permission from the American Society for Microbiology (López-Meza,
J.E. and Ibarra, J.E.; Appl. Environ. Microbiol, 1996 April; 62(4): 1306-1310) Photo
courtesy of Doctor J.E. López-Meza.
세균 살충제
• 토마토 각질벌레, 옥수수 나무좀, 매미나방을 죽임
• 후에 이 균 유전자를 식물세포에 직접 삽입 (Bt corn)
Biotechnology on the Farm
• Bacterial insecticides
– Bt
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Gene for toxin cloned and placed in A. tumefaciens
Agrobacterium works as ferry so plants express biological insecticide
Bt corn first crop to be used commercially
Bt cotton also being used
– Bacillus sphaericus
• Mosquito toxin
• Toxin gene inserted into Asticcacaulis excentris
– Advantages over B. sphaericus
» Easier to grow in large quantities
» Better tolerance to sunlight
» Floats on water, where mosquito larva exist
Biotechnology on the Farm
• Bacterial insecticides
– Photorhabdus luminescens
• Toxin called Pht
• Infect broad range of hosts, including cockroaches(바퀴)
• Efforts now underway to clone and express toxin in other species
Biotechnology on the Farm
• Viral and fungal insecticides
– Baculoviruses
• Infect lepidopterans(인시류)
• Engineered with scorpion(전갈) toxin to paralyze caterpillars(모충)
– Grape fan-leaf virus (GFLV)
• Transmitted by nematodes(선충류)
• Exogenous expression of capsid protein in grapes prevents infection
by virus
• Protection of grape crops from GFLV disease
– Lagenidium giganteum
• Fungus that attacks soybean- and rice-damaging mosquitoes
• Marketed as Laginex
Biotechnology on the Farm
• Biotech replacements
– Endowing insects with suicide genes
• Cotton bollworms
– Introduction of lethal gene that activates in offspring
• Medflies (Mediterranean fruit flies)
– Attempts to find and introduce same sort of lethal gene
• Ice-minus bacteria
– Pseudomonas syringae
» Encourage ice formation and frost on plants
» Bacteria lacking proteins that help form ice were engineered
» These new recombinants are being used to crowd out wild-type
bacteria
» Expectation is that recombinant P. syringae will now allow frost only
at lower temperatures, therefore extending growing season
Biotechnology on the Farm
• Resistance to herbicides(제초제)
– Herbicides are weed-killing chemicals used to clear fields before
planting “good” crops
– However, herbicides kill weeds and “good” crops
– Need to engineer “good” crops with herbicide resistance
• Herbicides kill weeds, but not “good” crops
– Common herbicide is glyphosate (Roundup®, Tumbleweed®)
• E. coli express enzymes that are more resistant than plant enzymes to
glyphosate activity
• The genes for these enzymes have been cloned into the Ti plasmid
• Delivered to plants via Agrobacterium tumifaciens
• By 2001, over 60% of US tobacco contained this resistance gene
• Now weeds killed by glyphosate, but not tobacco (or soybeans)
글리포세이트 저항성 유전자 변형
Biotechnology on the Farm
• Pharm animals
– Dairy cows
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Bovine growth hormone (BGH; somatotropin) expressed by E. coli
Injected into beef and dairy cows
Increased growth of muscle, bone, and milk production
Pigs also injected to decrease amount of untrimmable fat
– Sheep
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Production of recombinant sheep epidermal growth factor
Injected into sheep
Eases removal of wool
Fleece can come off sheep in single, unmutilated sheet
Biotechnology on the Farm
• Genetically modified foods
– Examples
• FlavrSavr tomato
– Antisense RNA to polygalacturonase
– Reduced activity of enzyme, which degrades pectin
– Increased shelf-life of these genetically modified tomatoes
– Never marketed because of bad public response
Figure 15.10: The
Development of the the
FlavrSavr Tomato.
유전자 변형식품
Biotechnology on the Farm
• Genetically modified foods
– Examples
• Improved canola oil
– Addition of genes to produce lauric acid in canola seeds
– Adds nutritional value to canola oil
• Bruise resistant potatoes
• Yellow squash (Freedom 2) that resists two plant viruses
• Salt-tolerant tomato
– Genes obtained from Arabidopsis
– Aids growth during salt stress, making over 25% of irrigated land
now arable again
• Plants that speed up or delay flowering
• Grain plants that grow to shorter heights
– Increase size of grain
– Decrease wind damage
Biotechnology on the Farm
• Veggie vaccines(야채백신)
– Transgenic plants that carry microbial vaccines
– Simply eating recombinant fruits and vegetables would “immunize”
the individual
– Portable to the Third World
– First experiments with potatoes expressing toxin made by harmful
E. coli
• Limited success
– Now trying tomatoes and bananas
• More palatable
– Many obstacles