Chapter 11 Key Concepts

Define lithotroph and organotroph

A lithotroph is an organism that uses an inorganic substrate (usually of mineral origin) to obtain reducing equivalents for use in biosynthesis An organotroph is an organism that obtains hydrogen or electrons from organic substrates

What is an aerobic chemolithotroph?

A microorganism that obtains energy by oxidizing reduced inorganic chemicals using oxygen as a terminal electron acceptor. What is an aerobic chemoorganotroph?| A microorganism that oxidizes organic compounds to obtain energy, using oxygen as a terminal electron acceptor

Define nitrogen fixation

Able to convert nitrogen gas to ammonia, which can then be incorporated into cell materials. An exclusive ability to prokaryotes.

What do methanogens, sulfur- and sulfate-reducing bacteria, Clostridium species, lactic acid bacteria, and Propionibacterium species all have in common?

They are all anaerobic chemotrophs, which means they harvest energy by oxidizing chemicals.

Why is it important for heterocysts to not have a functional photosystem II?

They cannot generate oxygen, so nitrogenase will be protected from oxygen during nitrogen fixation

Describe the characteristics of hydrogen-oxidizing bacteria

Aerobic chemolithotrophs (use inorganic chemicals as energy sources, use aerobic respiration--oxygen is the final electron acceptor). Thermophilic bacteria that oxidize hydrogen gas as an energy source. One of the earliest bacterias to exist on earth. Thermophilic and live in hot springs.

Describe the characteristics of sulfur-oxidizing bacteria

Aerobic chemolithotrophs. Sulfur-oxidizing bacteria: gram negative rods or spirals that sometimes grow in filaments. Obtain energy by oxidizing elemental sulfur and reduced sulfur compounds (hydrogen sulfide and thiosulfate). Aerobic--oxygen serves as a terminal electron acceptor, generating sulfuric acid. Two types: filamentous and unicellular. Filamentous: Beggiatoa, Thiothrix. Form a 'mesh'. Found in sulfur springs and sewage-polluted waters. Overgrowth causes blockages in waste treatment facilities. Unicellular: Thiobaccilus, Acidithiobacillus. Some species produce enough acid to lower pH to 1, killing wildlife. Can be used to recover metals and prevent acid rain from sulfur buildups.

Describe the characteristics and habitats of lactic acid bacteria.

Aerotolerant anaerobic chemoorganotrophs that rely on fermentation.. Gram positive bacteria that produce lactic acid as their major end product of their fermentation. Includes streptococcus, enterococcus, lactococcus, lactobacillus, and leuconostoc. Streptococcus: inhabit the oral cavity, generally as part of normal microbiota. Some strains can be used to make yogurt. Others are pathogens--most important is S. pyogenes. Lactobacillus: mouth and vagina. Create low pH that helps prevent vaginal infections.

Compare and contrast the characteristics and habitats of the extreme halophiles and extreme thermophiles.

All are members of the domain Archaea. Extreme halophiles are aerobic or facultatively anaerobic chemoheterotrophs. Found in high numbers in salty environments such as salt lakes, soda lakes, and brines. Require a minimum of 9% sodium. Produce pink pigments. Include Halobacterium, Halorubrum, Natronobacterium, and Natronococcus. Extreme thermophiles are obligate anaerobes. Found near volcanic vents and fissures that release sulfuric gases and other hot vapors, also found hydrothermal vents in the sea and hot springs. Three types: methanogens, sulfur reducing (obligate anaerobes that use sulfur as terminal electron acceptor), and nanoarchaeum (grows as tiny, 400nm spheres attached to the surface of ignicoccus species), sulfur oxidizers (obligate aerobes that oxidize sulfur compounds using oxygen as terminal electron acceptor), and extreme acidophiles (grow optimally at extremely high temperatures and extremely low pH).

Define phototroph

An organism that manufactures its own food from inorganic substances using light for energy.

Describe the characteristics and types of purple bacteria

Anoxygenic phototrophs. Purple bacteria are gram negative organisms that appear red, orange, or purple due to their light harvesting pigments. Components of their photosynthetic apparatus are all contained within the cytoplasmic membrane. Purple sulfur bacteria grow as colored masses in sulfur-rich aquatic habitats. Use hydrogen sulfide to generate reducing power, although some can use other inorganic or organic molecules. Most are strict anaerobes and phototrophs. Have gas vesicles.Examples: chromatium, thiospirillum, thiodictyon. Purple non-sulfur bacteria are found in a wide variety of aquatic habitats. Prefer using organic molecules rather than hydrogen sulfide for reducing power. No gas vesicles. Most can grow aerobically in the absence of light using chemotrophic metabolism. Examples: rhodobacter, rhodopseudomonas.

Describe the characteristics of green bacteria

Anoxygenic phototrophs. Gram negative organisms that are green or brown in color. Grow in sulfur-rich aquatic environments. Green sulfur bacteria: Like purple sulfur bacteria, use hydrogen sulfide as source of reducing power. Form sulfur granules outside of the cell. Pigments are located in chlorosomes. No flagella. Have gas vesicles. All are strict anaerobes. Examples: chlorobium, pelodictyon. Filamentous anoxygenic phototrophic bacteria: Metabolically diverse--some use organic compounds and some use chemotrophic metabolism and can grow in the dark. Form multicellular arrangements and exhibit gliding motility. Most thoroughly studied are the chloroflexus genus that grow in hot springs. Many have chlorosomes, but they are not related to green sulfur bacteria.

Compare and contrast Agrobacterium species and rhizobia.

Both are associated with plants, but use very different means to obtain nutrients from plants. Agrobacterium are gram negative that cause plant tumors to genetically alter plants for their own benefit through a plasmid that encodes the ability to synthesize plant growth hormones and synthesize opine--which agrobacterium use as a nutrient source. Rhozobia are gram negative that form relationships with legumes. Live within cells in nodules formed at the roots of plants and synthesize leghemoglobin, a protein that binds and controls levels of oxygen--allowing plants to fix nitrogen in the absence of oxygen.

Describe the characteristics of chemolithotrophs.

Chemolithotrophs--means they obtain energy by oxidizing inorganic chemicals such as hydrogen gas. Use CO2 or sulfur as terminal electron acceptor. Most are members of the domain archaea.

Define chemotroph

Chemotrophs are organisms that obtain energy through the oxidation of electron donors in their environments via electron transfer. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs).

Name and describe four bacterial groups that form resting stages.

Endospore formers: Bacillus and Clostridium are the most common bacteria that form endospores. Azotobacter: gram negative bacteria that live in soil. Can form a type of resting cell called a cyst that can withstand drying and UV radiation, but not heat. Due to its extremely high respiratory rate, it can fix nitrogen in aerobic conditions--rare because oxygen inactivates nitrogenase. Myxobacteria: are aerobic and gram negative. Cells secrete a slime layer when conditions are favorable. When nutrients are low, cells begin to come together and form a brightly-colored fruiting body, with microcysts inside. Streptomyces: Includes more than 500 species of aerobic, gram positive bacteria. Resemble fungi in pattern of growth: form a mycelium. At the tips of the mylecium, spores called conidia develop. Produces useul antibiotics.

Describe the characteristics and habitats of Clostridium species.

Examples: C. tetani, Obligate anaerobic chemoorganotrophs that use fermentation to obtain energy. Ferment a wide range of compounds, including sugars and cellulose and even amino acids (bad smelling end products). Common in soil and digestive tract. Gram positive, and can form endospores. Cells that develop from endospores are responsible for a variety of diseases, including tetanus, gangrene, botulism.

Describe the characteristics and habitats of sulfur- and sulfate-reducing bacteria.

Examples: Desulfovibrio When sulfur compounds are used as terminal electron acceptors, they become reduced to form hydrogen sulfide, the compound responsible for the rotten egg smell of many anaerobic environments. Also corrodes metals. Bacteria generally live in mud that has organic material and oxidized sulfur compounds. Hydrogen sulfide turns mud and water black when it reacts with iron. Mesophiles or thermophiles. Some are archaea, and these are usually hyperthermophiles, living in environments like hydrothermal vents.

Describe the characteristics and habitats of methanogens

Examples: methanospirillum, methanosarcina Methanogens are archaea chemolithotrophs. They generate ATP by oxidizing hydrogen gas, or alternative energy sources like formate, methanol, or acetate. They use CO2 as a terminal electron acceptor, and this process generates methane. Found in anaerobic environments where hydrogen gas and CO2 are available. Not found in environments with high sulfate, nitrate, or other inorganic electron acceptors, because microorganisms that use these electron acceptors would have a competitive advantage. Swamps, marine sediments, rice paddies, and digestive tracts. Often grow in association with fermentative bacteria.

acid fast. Resistant to many disinfectants and antibiotics. Pseudomonas: gram negative rods that have polar flagella and often produce pigments. Common environmental bacteria that can degrade a wide variety of compounds. Thermus: gram negative. Thermophilic: the source of Taq polymerase used in PCR. Deinococcus: gram positive. Wall has multiple layers-- extraordinarily resistant to gamma radiation. In the future, may be able to help clean soil and water contaminated with radioactive waste. Define and describe the representative facultative anaerobes (Corynebacterium, enterobacteriaceae, vibrio)

Facultative anaerobes preferentially use aerobic respiration if oxygen is available, but can ferment if no oxygen is present. Corynebacterium are widespread in nature and gram positive. Many live harmlessly in the throat, but some can cause the disease diphtheria Enterobacteriaceae are gram negative and mostly reside in the intestinal tract. Those that ferment lactose are coliforms, their presence in water serves as an indicator of fecal pollution. Vibrio are typically found in marine environments because they require sodium to grow. Gram negative.

Describe members of the family Enterobacteriaceae and what distinguishes coliforms from other members of this family.

Members of this family are often referred to as interecs, and include enterobacter, klebsiella, and proteus as well as most strains of e. Coli. Those that ferment lactose are coliforms, their presence in water serves as an indicator of fecal pollution.

Define and describe the representative obligate aerobes (micrococcus, mycobacterium, pseudomonas, thermus, and deinococcus.

Obligate aerobes obtain energy using respiration exclusively, none can ferment. Micrococcus: gram positive cocci found in soil and on dust particles, objects, and skin. Often airborne. Form pigmented colonies. Mycobacterium: not gram positive or negative due to high lipid content in cell wall. Waxy cell wall resists staining

Describe the characteristics and habitats of Propionibacterium species.

Obligate anaerobic chemoorganotrophs that rely on fermentation. Gram positive pleomorphic rods that produce propionic acid as their main fermentation end product. Can also ferment lactic acid--so they can extract energy from the waste products of other bacteria. Valuable to the dairy industry because their end products are important in Swiss cheese production

Describe the characteristics of nitrifiers

Oxidize ammonia or nitrate as energy source. Aerobic chemolithotrophs (use inorganic chemicals as energy sources, use aerobic respiration--oxygen is the final electron acceptor). Ex: Nitrosococcus, nitrobacter, nitrococcus. Converts fertilizers to a form easily leached from soils. Depletes oxygen in waters polluted with ammonia-containing wastes.

Describe the characteristics of chemoorganotrophs.

Oxidize organic compounds, such as glucose, to obtain energy. Anaerobic chemoorganotrophs often use sulfur or sulfate as a terminal electron acceptor.

Describe the characteristics of cyanobacteria, including how nitrogen-fixing species protect their nitrogenase enzyme from O2.

Oxygenic phototrophs. Cyanobacteria are a diverse group of photosynthetic gram-negative bacteria that inhabit a wide range of environments, including freshwater and marine habitats, soils, and rock surfaces. Some are able to convert nitrogen gas to ammonia, which can then be incorporated into cell materials--nitrogen fixation. Can also incorporate CO2 into organic material--good for decreasing atmospheric CO2 buildup. Have special pigments called phycobiliproteins that contribute to their blue-green color. Nitrogenase, the enzyme that catalyzes nitrogen fixation, is destroyed by oxygen. To protect nitrogenase, some cyanobacteria isolate the enzyme by restricting the process of nitrogen fixation to heterocysts--specialized, thick walled cells.

Name three discoveries from van Niel's work on purple bacteria?

Purple bacteria require light for growth, but unlike plants and algae, do not produce oxygen. Purple bacteria oxidize hydrogen sulfide as they fix CO2 Photosynthetic reactions of all photosynthetic are remarkably similar, except that purple bacteria use hydrogen sulfide in place of water and produce oxidized sulfur components instead of oxygen. This led researchers to believe that oxygen generated from plants and algae does not come from CO2, but water.

Describe the examples of the five mechanisms aquatic bacteria use to maximize nutrient acquisition and retention.

Sheathed (sphaerotilus, leptothrix): form chains of cells enclosed within a protective sheath. Help bacteria attach to favorable habitats. Swarmer cells move to new locations. Gram negative. Prosthecate (caulobacter, hyphomicrobium): appendages increase surface area. Gram negative. Nutrients from other organisms: Bdellovibrio prey on other bacteria. Bioluminescent bacteria form symbiotic relationships with specific types of squid and fish. Legionella live within protozoa. Epulopiscium live within the intestine of surgeonfish. Moving by unique mechanisms: Spirochetes have a spiral share and endoflagella that allow them to move through thick, viscous environments. Magnetospirillum use magnetic crystals to move in water and sediment. Form storage granules to store nutrients: Spirillum forms volutin granules to store phosphate. Thioploca and Thiomargarita store sulfur (energy source) and nitrate (terminal electron acceptor).

Compare and contrast the examples of bacteria that use animals as habitats.

Skin: Staphylococcus (facultative anaerobes) and propionic bacteria (anaerobic) thrives on the skin's dry and salty environment. Propionic bacteria live in the anaerobic microenvironments of the skin. Mucous membranes: mucous membranes provide a habit for numerous kinds of bacteria, including streptococcus (respiratory), corynebacterium (respiratory), lactobacillus (vagina), clostridium (intestine), enterobacteriaceae (intestine). Obligate intracellular parasites: cannot reproduce outside the host cell--supplied by host cell with compounds they would otherwise need to synthesize, so they lack the ability to make substances needed for extracellular growth. Include members of the genera Rickettsia, Orientia, Ehrlichi (all cause diseases spread by ticks and lice), Coxiella (causes Q fever, can survive outside of host cells), Chlamydia, Chlamydophila (initially exist as non-infectious, and then differentiate into smaller, dense elementary bodies--infectious form), and Wolbachia ( infects arthropods and parasitic worms. Resides within worms that cause river blindness and elephantiasis).

Describe the characteristics of anoxygenic phototrophs.

The earliest photosynthesizing organisms. Purple and green bacteria. Employ only a single photosystem and are unable to use water as an electron donor for reducing power. Use hydrogen sulfide or organic compounds rather than water as a source of electrons when making reducing power for biosynthesis. This is why they are anoxygenic or do not generate O2