Microbes and Food 12. Beginning Our Meal A glass of wine –Grape juice that is fermented by yeast...

Microbes and Food

12

Beginning Our Meal

• A glass of wine– Grape juice that is fermented by yeast– Red wine

• Black grapes

• Includes skins and stems

– White wine• Black or green grapes

• No skins or stems

– Yeast plentiful in vineyards and orchards• Utilize sugars from fruit for energy

• Apples: applejack (alcoholic apple juice)

• Peaches: peach-flavored ethanol

• Barley: barley-flavored ethanol (beer)

Beginning Our Meal

• The appetizers– Cheese

• Microbial conversion of casein (milk protein)

• Curdling

• Curds are “unripened cheese:” cottage cheese

• “Ripened cheese”

– Curds washed

– Salt added

– Cultures of microbes added» Example: Swiss cheeseo Lactobacillus produce acids that lead to sournesso Propionibacterium produce organic chemicals and CO2o Creation of taste and holes

Beginning Our Meal

• bread– Bread

• Flour and water

• Saccharomyces cerevisiae

• Presence of grain protein, gluten

• CO2 production by yeast

• Dough rises

• Other microbes can be added

– Usually Lactobacillus

– Degrade starch in flour

Continuing Our Meal

• The main course– Sausages

• Dry or semi-dry fermented meats

• Pepperoni

• Thuringer

• Polsa

• Ground meat plus curing and seasoning agents

• Microbes multiply

• Give sausage unique taste

Continuing Our Meal

• The main course– Sauerkraut

• Fermented cabbage

• Gram-positive cocci

– Leuconostoc

– Lactobacilli

– Bacteria normally found on leaves and tissues of cabbage

• Shred cabbage

• Add salt

– Ruptures cell walls of cabbage

– Releases juices, adds flavor

• Air-tight packaging

• Bacteria ferment

– Leuconostoc produce lactic and acetic acids

– Then Lactobacillus produces more lactic acid

Continuing Our Meal

• The main course– Pickled cucumbers

• Dill, sour, sweet pickles

• Cucumbers

• High salt solution

• Aging tank

– Enterobacter» CO2 production

» Creates anaerobic conditions

– Leuconostoc and Lactobacillus ferment to create lactic and acetic acids

– Softening and souring of cucumbers

– Yeasts also present

– Herbs and spices

Continuing Our Meal

• A refreshing beer– Barley grains– Predigested in process called malting

• Barley steeped in water• Barley enzymes digest starch into maltose, a simpler carbohydrate

– Malt now ground with water (mashing)– Liquid portion (wort) removed– Dried flower of Humulus lupulus (hops) added

• Adds flavor• Adds color• Stabilizes mixture

– Fluid is filtered– Saccharomyces yeast added

• CO2 production• Then fermentation and production of about 4% alcohol

Continuing Our Meal

• A refreshing beer– Different species of yeast

• S. cerevisiae

– Dark, cloudy beer (English stout or ale)

– Called top yeast because they are carried to top of vat

– Warmer fermentation temperature (20 °C)

• S. carlsbergensis

– Slower fermentation

– Lighter, clearer beer (Pilsener or lager)

– Less alcohol

– Called bottom yeast because less frothing, settle to bottom of vat

– Colder fermentation temperature (15 °C)

• Ice beer

– Fermentation at still colder temperatures

Microbes and Agriculture

No Microbes, No Hamburgers

15

Microbes on the Farm

• Connecting the nitrogen dots– 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

Microbes on the Farm: The Nitrogen Cycle

Figure 15.2: A simplified nitrogen cycle


• Connecting the nitrogen dots– Free-living nitrogen-fixers

• 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


• Connecting the nitrogen dots– Symbiotic nitrogen-fixers

• Rhizobium

• Bradyrhizobium

• Live in nodules on roots of legumes

– Soybeans

– Alfalfa

– Peas

– Clover

– Beans

• Formation of bacteroids

Fig. 15.1: A) Nodules containing nitrogen-fixing 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)

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• Those remarkable ruminants– Ruminants

• Cud-chewers

– Cattle

– Sheep

– Deer

– Goats

– Camels

– Buffalo

• Diet of plants, grasses, high-carbohydrate plants

• Still produce proteins

• Consumed in human diet for meat


• 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

• 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

• Mixture is called cud


• Those remarkable ruminants– Cud regurgitated– Rechewed and remixed with saliva– Reswallowed to rumen to continue fermentation and breakdown– Cud finally passes to omasum and the abomasum

• Proteases release amino acids from proteins

• Nutrients absorbed from intestines

Microbes on the Farm: Microbes and the Rumen

Fig. 15.3 The rumen of a cow stomach


• Those remarkable ruminants– Non-ruminant herbivores

• Horses

• Rabbits

• Guinea pigs

• Still eat grasses, like ruminants

• Cecum contains microbes that perform same tasks as those in rumen

– Coprophagous herbivores• Reconsume fecal pellets

• Gives second pass through intestine to capture maximum nutrients


• At the dairy plant– 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


• 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


• At the dairy plant– Acidophilus milk

• Pasteurized milk

• L. acidophilus added

• Bacteria colonize intestines

• L. acidophilus crowd out harmful microbes

– Butter• Streptococci and Leuconostoc added to sweet cream

Fig. 15.5 Fermented Milk Products

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• Of curds and whey– Cheese

• Produced from casein

• Three steps

– Curd formation» 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


• Of curds and whey– Cheese

• Third step

– Curd ripening and resultant cheeses

» Camembert» Cheddar» Pecorino Romano» Limburger» Roquefort» Gorgonzola» Danablue» Blue cheese

Figure 15.6: Various cheeses produced by microbes

Microbes and the Environment

No Microbes, No Life

16

The Cycles of Nature

• The Earth ecosystem– Microbes are an important part of all ecosystems

• Biota

• Habitat

– Freshwater lakes

– Marine environments

– Soil

• Microbial community

– Energy enters ecosystem by sunlight• Photosynthetic organisms, called producers

• Nutrients used by other organisms, consumers

• Energy from consumers recycled by decomposers

• Most energy dissipated as heat

The Cycles of Nature: Energy Pathways in a Forest Ecosystem

Figure 16.1: The Pathway of energy in a forest community


• The Earth ecosystem– Energy constantly being replaced by sunlight– Chemicals constantly being recycled

• Carbon

– CO2 captured as carbohydrates

– Carbohydrates broken down to CO2

• Nitrogen

• Sulfur

• Other elements


• The carbon cycle– CO2 captured by photosynthetic organisms and converted to

carbohydrates• Chlorophyll and sun’s energy

– Photosynthetic organisms consumed by animals, fish, humans• Carbohydrates utilized for energy and structures

– Majority of carbon returned to soil when consumer dies• Some carbon returns to atmosphere as CO2

The Cycles of Nature: The Carbon Cycle

Figure 16.2: A simplified carbon cycle


• The carbon cycle– Soil decomposers

• Billion of bacteria, fungi, other microbes

• Consume organic matter

• Release CO2 back to environment, plants

– Aerobic and anaerobic breakdown– Carbon cycle in the deep sea

• Archaea in ocean floor sediment

• Intake as much as 300 million tons of methane per year

• Convert methane into other carbohydrates that can be used by neighboring microbes

– Humus– Compost


• The carbon cycle– Coal– Petroleum– Microbes that break down these complex carbon-containing

mixtures• Jet fuel

• Herbicides

• Pesticides

• Plastics

• Shale


• The sulfur cycle– Sulfur important for amino acids and coenzymes

• Cysteine

• Methionine

• Forms dithiol bridges

– Most sulfur in nature exists as sulfate• Used as electron acceptor by some microbes

• End product is H2S

• Combines with iron to form iron disulfide (FeS2), black product

• H2S smells like rotten eggs

• H2S corrodes iron and steel pipes buried in soil


• The sulfur cycle– H2S used by purple sulfur and green sulfur bacteria

• Electron donor

• Converted to elemental sulfur

• Sulfur stored inside cells as granules

– H2S use by colorless sulfur bacteria

• Thiobacillus and Beggiatoa convert H2S to sulfate ions under aerobic conditions

• Derive energy from the conversion

• Generate ATP

• Growth in acid-mine waters

• Also break down FeS2 into pyrite and produce sulfuric acid

• Sulfuric acid creates insoluble yellow precipitate

The Cycles of Nature: Acid-Mine Waters

Figure 16.3: Acid mine drainage

Courtesy of D. Hardesty/USGS


• The sulfur cycle– Beggiatoa at deep sea vents

• Black smokers

• 250 atmospheres of pressure

• 300 °C

• Provide nutrients to animals living near vents

– Thiomargarita namibiensis


• The nitrogen cycle– Soil microbes and protein decomposition

• Yields mixture of amino acids• Further broken down into inorganic compounds and ammonia• Nitrosomonas converts ammonia to nitrite• Nitrobacter converts nitrite to nitrate

– Nitrate usage• Some used by plants• Most broken down by microbes and released to atmosphere as N2

• Return of N2 to organisms is called nitrogen fixation– Bacillus– Clostridium– Azobacter– Rhizobium– Some cyanobacteria– Some yeasts

The Cycles of Nature• The phosphorus cycle

– Phosphorus released from rocks• Worn away by rushing water• Enters sea as dissolved phosphates• Unicellular algae and microbes take up phosphates• Produce nucleic acids, phopholipids, ATP• These organisms are consumed and phosphorus moves up the food chain• Phosphorus part of bones and shells• When these animals die, phosphorus returned to sea

Figure 16.5: The phosphorus

cycle in nature


• The oxygen cycle– Cyanobacteria began releasing O2 as photosynthetic byproduct

billions of years ago– Respiration

• Animals, plants, and microbes

• Complete the oxygen cycle

• Trap oxygen in water

Preserving the Environment

• Bioremediation– Use of microbes to help clean up environment

• Pseudomonas species at Exxon Valdez spill site

• Degradation of polychorinated biphenyls (PCBs)

• Methane metabolizing microbes that break down trichloroehtylene (TCE)

• Biological breakdown of trinitrotoluene (TNT) at weapons manufacture sites

• Arthrobacter to degrade oil and allow plant growth in Iraq


• The pollution problem– Approximately 75% of humans have no clean drinking water– As many as 3.3 billion people have only contaminated water– Average US citizens use about 100 gallons of clean water each

day– Water pollution starts with sewage and industrial wastes

• Dairies

• Food-processing plants

• Meat-packing plants

• Petroleum refineries

• Paper mills

• Pharmaceutical companies

– Fertile ground for microbial growth

Preserving the Environment: The Pollution Problem

Figure 16.9: The death of a river


• The pollution problem– Toxic substance enter water stream– Marine and freshwater species die– Decomposing microbes flourish and consume all available oxygen– Lack of oxygen prevents growth of other protozoa, fish, plants, etc.– These species also die and accumulate on bottom– Anaerobic Desulfovibrio and Clostridium species thrive and create

more toxic substances– Corrosion of water pipelines– Water as a vehicle for pathogenic microbes


• Microbe detection methods– Infectious disease microbes in water supplies

• Typhoid fever bacteria

• Cholera bacteria

• Hepatitis A virus

• Polio virus

– Use of indicator organisms• Gram-negative rods normally found in human and animal large

intestines (coliforms)

• E. coli is typically used organism


• Microbe detection methods– Membrane filtration technique– Most probable number (MPN)


• Microbe detection methods– PCR for E. coli– Limulus polyphemus (horseshoe crab) red blood cells

• Water treatment– Required to remove harmful microbes– Needed to improve clarity, taste, odor– May be needed to remove calcium and magnesium (softening)– Frequently fluoride is also added

Preserving the Environment: Water Treatment

Figure 16.10: Water purification


• Water treatment– Coagulation– Filtration– Chlorination– Ad hoc treatment

• Boiling water source

• Safe to drink, but not sterile

• Chlorine or iodine tablets

• Chlorine bleach (1/2 tsp. per 2 gallons of water, 30 minutes)

• “Poison pen”

– Dissolved salt tablet

– Electric jolt creates antimicrobial compounds

– Dump into quart of water to purify it

Microbes and Food 12. Beginning Our Meal A glass of wine –Grape juice that is fermented by yeast...

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Transcript of Microbes and Food 12. Beginning Our Meal A glass of wine –Grape juice that is fermented by yeast...