Brock Biology Chapter 15: Bacterial Diversity

What is metabolic diversity in bacteria?

Defined in terms of cellular processes supporting growth.

How is ecological diversity defined?

In terms of microbial interactions between organisms and their environments.

What is phylogenetic diversity?

Defined by evolutionary relationships between organisms, including diversity of phyla, genera, and species.

What is the most common method to define phylogenetic diversity?

By ribosomal RNA phylogeny.

What are three reasons metabolic and ecological traits are shared by divergent organisms?

Gene loss, convergent evolution, and horizontal gene transfer.

What are anoxygenic phototrophs?

Phototrophs that do not generate O2 as a product and use other electron donors like H2, Fe2+, or H2S.

What are the two types of reaction centers in phototrophic bacteria?

FeS and Q-type reaction centers.

What is the role of pigments in phototrophic bacteria?

They harvest energy from light and transfer it to membrane-bound reaction centers.

What is the significance of thylakoids in cyanobacteria?

They are specialized membrane systems that increase the ability to harvest light energy.

What are the five morphological groups of cyanobacteria?

Chroococcales, Pleurocapsales, Oscillatoriales, Nostocales, and Stigonematales.

How do cyanobacteria fix nitrogen?

Many unicellular cyanobacteria fix nitrogen only at night, while filamentous cyanobacteria form heterocysts.

What is a heterocyst?

A specialized cell in some cyanobacteria that provides an anoxic environment for nitrogen fixation.

What are the key genera of cyanobacteria?

Prochlorococcus, Crocosphaera, Synechococcus, Trichodesmium, Oscillatoria, Anabaena.

What is the ecological importance of cyanobacteria?

They contribute significantly to marine photosynthesis and are a dominant input of new nitrogen in oceans.

What metabolic products can cyanobacteria produce?

Potent neurotoxins and toxic blooms, as well as geosmin in water.

What is the significance of gas vesicles in cyanobacteria?

They regulate buoyancy, allowing cells to position themselves in optimal light conditions.

What is the role of chlorophyll in cyanobacteria?

They produce chlorophyll a and accessory pigments for photosynthesis.

How do cyanobacteria contribute to freshwater ecosystems?

They can develop blooms and are more tolerant of extreme conditions than eukaryotic algae.

What is the primary photosynthetic pigment in cyanobacteria?

Chlorophyll a.

What is photoheterotrophy in cyanobacteria?

The ability to assimilate simple organic compounds in light.

What is the function of peptidoglycan in cyanobacterial cell walls?

It provides structural support and protection.

What is the significance of the Calvin cycle in cyanobacteria?

It is the process by which they fix CO2 during photosynthesis.

What are the two main types of photosystems found in cyanobacteria?

FeS and Q-type photosystems.

What is the evolutionary significance of cyanobacteria?

They were the first oxygen-evolving phototrophs.

What type of environments do cyanobacteria thrive in?

They are found in diverse environments, including extreme conditions like hot springs and saline lakes.

What is the primary role of cyanobacteria in ocean ecosystems?

They are the most abundant ocean phototrophs, contributing significantly to marine productivity.

What are purple sulfur bacteria?

Anoxygenic phototrophs that use hydrogen sulfide as an electron donor for photosynthesis.

Name three key genera of purple sulfur bacteria.

Chromatium, Thermochromatium, Ectothiorhodospira.

Where are purple sulfur bacteria typically found?

In illuminated anoxic zones such as lakes, marine sediments, and sulfur springs.

What gives purple sulfur bacteria their color?

Carotenoids, which are accessory pigments for light harvesting.

What type of photosystem do purple sulfur bacteria use?

Q-type photosystem.

How do purple sulfur bacteria fix carbon?

Using the Calvin cycle.

What happens to hydrogen sulfide during the autotrophic growth of purple sulfur bacteria?

It is oxidized to elemental sulfur, which is deposited as granules.

What are the two families of purple sulfur bacteria?

Chromatiaceae and Ectothiorhodospiraceae.

How do Chromatiaceae store sulfur?

They store sulfur granules inside the periplasm.

What is a characteristic of Ectothiorhodospiraceae?

They deposit sulfur outside cells and have lamellar intracellular photosynthetic membrane systems.

What is the habitat of Thermochromatium?

Sulfidic hot springs, where it forms thin biofilms.

What are purple nonsulfur bacteria?

Metabolically versatile microbes that are typically photoheterotrophs.

Name four key genera of purple nonsulfur bacteria.

Rhodospirillum, Rhodoferax, Rhodopseudomonas, Rhodobacter.

What type of gene cluster do purple nonsulfur bacteria share?

Photosynthetic gene cluster (PGC).

What is the primary energy source for purple nonsulfur bacteria?

Light, while using organic compounds as carbon sources.

How do aerobic anoxygenic phototrophs differ from purple nonsulfur bacteria?

They use light as a supplemental energy source but are obligate aerobic heterotrophs.

What is nitrogen fixation?

The process of converting nitrogen gas into ammonia, which can be assimilated.

What are diazotrophs?

Organisms that fix nitrogen gas into ammonia.

What is required for nitrogen fixation?

ATP and nitrogenase.

What are symbiotic diazotrophs?

Microbes that have relationships with plants, animals, and fungi, providing fixed nitrogen to the host.

Give an example of a symbiotic relationship involving diazotrophs.

Symbiosis between rhizobia and leguminous plants.

What are free-living diazotrophs?

Diazotrophs that do not rely on a host for nitrogen fixation.

How do free-living diazotrophs protect nitrogenase from oxygen?

By growing anoxically or in low oxygen environments.

What is unique about Azotobacter chroococcum?

It can grow on hydrogen sulfide without molybdenum and forms alternative nitrogenases.

What do denitrifiers do?

They grow by anaerobic respiration of inorganic nitrogen compounds to produce gaseous nitrogen.

What type of bacteria are nitrifiers?

Typically obligate aerobes that grow chemolithotrophically on reduced inorganic nitrogen compounds.

What is the significance of horizontal gene exchange in diazotrophic bacteria?

It has influenced the distribution and evolution of nitrogen-fixing capabilities.

What is nitrification?

The process often resulting from the sequential activities of ammonia oxidizers and nitrite oxidizers.

What do ammonia oxidizers typically oxidize?

Ammonia (NH₃) to nitrite (NO₂⁻).

What do nitrite oxidizers typically oxidize?

Nitrite (NO₂⁻) to nitrate (NO₃⁻).

What are the key genera of ammonia oxidizers?

Nitrosomonas, Nitrosospira, and Nitrosopumilus.

Where are nitrifying bacteria commonly found?

In soil and water, especially in areas with high concentrations of ammonia or nitrate.

What are the key genera of nitrite oxidizers?

Nitrospira and Nitrobacter.

What is the significance of Nitrospira?

It oxidizes nitrite and grows autotrophically, lacking extensive internal membranes.

What is denitrification?

The process of reducing nitrate or nitrite to nitrogen gas (N₂) or nitrous oxide (N₂O).

What are the key genera of denitrifying bacteria?

Paracoccus and Pseudomonas.

What type of respiration do denitrifying bacteria typically use?

Anaerobic respiration.

What is the ecological role of denitrifying bacteria?

They are important in agricultural soils, causing loss of nitrogen fertilizers and producing greenhouse gases.

What are dissimilative sulfate-reducers?

Bacteria that conserve energy through the reduction of sulfate (SO₄²⁻) or sulfur compounds.

What are the key genera of sulfate-reducing bacteria?

Desulfovibrio and Desulfobacter.

What is the metabolic diversity of sulfate-reducing bacteria?

They are morphologically and biochemically diverse, often obligate anaerobes.

What environments do sulfate-reducing bacteria inhabit?

Aquatic and terrestrial environments that become anoxic from microbial decomposition.

What are the characteristics of complete oxidizers among sulfate-reducing bacteria?

They oxidize acetate and other fatty acids completely to carbon dioxide (CO₂).

What distinguishes incomplete oxidizers among sulfate-reducing bacteria?

They are unable to oxidize acetate completely.

What are microbial predators?

Bacteria that consume other bacteria, found in various phyla including Proteobacteria and Bacteroidetes.

What is the predation method of epibiotic predators?

They attach to the prey's surface and acquire nutrients from the cytoplasm or periplasm.

What is unique about Bdellovibrio?

It is a periplasmic predator that invades and replicates within the periplasm of its bacterial prey.

What is the ecological impact of Bdellovibrio?

It is widespread in aquatic habitats and can form plaques similar to bacterial viruses.

What are the characteristics of Myxococcus?

They are social predators that swarm and collectively feed upon lysed prey.

What is the significance of horizontal gene exchange in denitrifying bacteria?

It allows for the widespread distribution of genes for denitrification across different species.

What types of environments do denitrifying bacteria thrive in?

They are found in agricultural soils and environments rich in organic carbon.

What is the role of sulfur-reducing bacteria in the sulfur cycle?

They participate in the reduction of sulfur compounds, contributing to the sulfur cycle in various ecosystems.

What are the metabolic pathways of sulfate-reducing bacteria?

They can reduce nitrate and sulfonates, and some can ferment organics.

What is a bdelloplast?

A spherical structure formed by Bdellovibrio after it penetrates the host cell wall.

What is Bdellovibrio?

A small, highly motile bacterium that preys on other bacteria, using host cytoplasmic contents as nutrients.

How does Bdellovibrio penetrate its prey?

It attaches to the prey, penetrates the cell wall, and replicates in the periplasm.

Which type of bacteria does Bdellovibrio primarily attack?

Gram-negative bacteria.

What type of respiration do Bdellovibrio bacteria perform?

They are obligate aerobes that oxidize amino acids and acetate.

What environments are Bdellovibrio widespread in?

Aquatic habitats, soils, and sewage.

What are myxobacteria known for?

Having the most complex behavior among known bacteria and forming multicellular structures called fruiting bodies.

What happens to myxobacteria when nutrients are exhausted?

They aggregate into mounds and differentiate into fruiting bodies containing myxospores.

What are spirochetes?

Morphologically unique, gram-negative, motile bacteria that are tightly coiled and typically slender.

What is the function of endoflagella in spirochetes?

They allow spirochetes to move in a corkscrew-like motion, enabling them to burrow through viscous materials.

Name a disease caused by Treponema.

Syphilis.

What is the habitat of Borrelia burgdorferi?

It is primarily found in humans and other mammals, transmitted via tick bites.

What is the primary characteristic of Leptospira?

They are strictly aerobic spirochetes that oxidize long-chain fatty acids.

What disease is associated with Leptospira interrogans?

Leptospirosis.

How do spirochetes differ from spirilla?

Spirochetes are flexible and thin, while spirilla are rigid and motile using polar flagella.

What is magnetotaxis?

The directed movement of bacteria in a magnetic field.

What are magnetosomes?

Chains of magnetic particles localized within cell membrane invaginations in magnetotactic bacteria.

Which bacterium is best characterized among magnetotactic bacteria?

Magnetospirillum magnetotacticum.

What type of environments do magnetotactic bacteria typically inhabit?

Near oxic-anoxic interfaces in sediments or stratified lakes.

What is the significance of myxospores in myxobacteria?

They are specialized resistant cells formed during the differentiation into fruiting bodies.

What role does chemotaxis play in myxobacteria?

It mediates the aggregation of vegetative cells in response to environmental cues.