Quiz 3 Web-Only

Question 1

What species produces a carcinogenic compound called aflatoxins? Aspergillus flavus

Answer 1

Aspergillus flavus

Question 2

Aspergillus flavus

Answer 2

A fungi that produces carcinogenic compounds called aflatoxins, flat-ringed planar compounds that can intercalate between bases of DNA and act as mutagens.

Question 3

Aflatoxin

Answer 3

Flat-ringed planar compounds produced by the fungus Aspergillus flavus that can intercalate between bases of DNA and act as mutagens.

Question 4

Myxobacteria

Answer 4

Gram-negative bacteria found in high-organic soils and decomposing plant residues.

• Rod shaped with flexible cell wall
• gliding motility (flagella-independent motility)
• Life cycle of Myxococcus xanthus (multicellular aggregation of fruting bodies)

Further reading:

Myxobacteria can move actively by gliding. They typically travel in swarms (also known as wolf packs), containing many cellskept together by intercellular molecular signals. Individuals benefit from aggregation as it allows accumulation of the extracellular enzymes that are used to digest food; this in turn increases feeding efficiency. Myxobacteria produce a number of biomedically and industrially useful chemicals, such as antibiotics, and export those chemicals outside the cell.

Question 5

gliding motility

Answer 5

Gliding motility is an energy-requiring, flagella-independent process that allows myxobacteria to move over a solid surface, im a pattern forming macroscopic waves called ripples

Question 6

Example of myxobacteria and life cycle

Answer 6

Myxococcus xanthus

Life cycle:

When starved, form multicellular aggregates called fruting bodies, in which some cells differentiate into dormant, stress-resistant myxospores. In some genera, myxospores are contained in sacs called sporangioles, which arise from stalks formed by vegetative cells. Myxospores germinate upon reintroduction to fresh media (aka not starved).

Question 7

Life cycle of Myxococcus xanthus

Answer 7

Myxococcus xanthus

Life cycle:

When starved, form multicellular aggregates called fruting bodies, in which some cells differentiate into dormant, stress-resistant myxospores. In some genera, myxospores are contained in sacs called sporangioles, which arise from stalks formed by vegetative cells. Myxospores germinate upon reintroduction to fresh media (aka not starved).

Question 8

fruiting bodies

Answer 8

Multicellular aggregates of Myxococcus xanthus that form vegetative cells when nutrients are low. Contain differentiated cells called myxospores that are stress-tolerant.

Question 9

myxospore

Answer 9

In multicellular aggregations of Myxococcus xanthus (called fruiting bodies), myxospores are differentiated cells that are stress-resistant, in some genera they are contained in sacs called sporangioles. When favourable conditions are restored, myxospores germinate and give rise to vegetative cells.

Question 10

sporangiole

Answer 10

In some genera of Myxococcus xanthus, myxospores are contained in sacs called sporangioles

Question 11

What bacteria was observed on rabbit dung in experiment 7?

Answer 11

Myxococcus xanthus

Question 12

Actinomycetes

Answer 12

Phylum of aerobic, Gram-positive bacteria with high C+G content that form branching filaments.

• Morphological intermediates between bacteria and fungi.
• Feature extensive, branched mycellum which, in some genera, give rise to conidiospores.

–Two types of mycelia, “vegetative” and “arial”

-Very important in most soils, Streptomyces produces 10,000 compounds including antibiotics, responsible for the smell of soil

Question 13

Two types of mycelia in Actinomycetes

Answer 13

–Two types of mycelia:

—Fine “vegetative” or “submerged” that grows into the substrate

—Thicker “arial”, may give the impression of powdery appearance due to the production of conidiospores

Question 14

conidiospores

Question 15

Streptomyces

Answer 15

Of phylum Actinomycetes, Streptomyces produces 10,000 compounds including antibiotics, responsible for the smell of soil

Question 16

TTC Deep

Answer 16

Triphenyl Tetrazolium Chloride

• “Selective”: Obligate aerobes - no growth (because of inoculation method)
• Differential: Tests for motility, red/pink colour change=growth (TTC accepts electrons, is reduced)
• Examples: Escherichia coli (motile), Staphylococcus aureus (nonmotile)

Question 17

What kind of plate, used in Demo 7B, selectively favours Actinomycetes?

Answer 17

Sodium caseinate agar plate

Sodium caseinate is the major protein source for the proteolytic organisms. Casein enzymic hydrolysate and yeast extract provide nitrogenous nutrients to the proteolytic organisms. Dextrose is the carbohydrate source. Protelolytic organisms form white or off-white precipitate around the colony. Organisms that are strongly proteolytic can breakdown the precipitate formed around the colonies to soluble components with the formation of an inner transparent zone. For the enumeration of proteolytic psychrotrophic bacteria, inoculated plates should be incubated for 10 days at 7°C.

Question 18

What proportion of photosynthesis is estimated to be carried out by microbes?

Answer 18

Over half of all photosynthesis on Earth

Question 19

What microbes are responsible for photosynthesis?

Answer 19

The Cyanobacteria (formerly known as Blue/Green algae) and Green and Purple bacteria

Question 20

What is the difference between the photosynthetic processes in Cyanobacteria and Green and Purple bacteria?

Answer 20

• Cyanobacteria use oxygenic photosynthesis (like plants), while Green and Purple bacteria use reduced compounds as the electron acceptor (anoxegenic photosynthesis)
• Cyanobacteria use chlorophylls as the light-collecting pigment (like plants), while Green and Purple bacteria use bacteriochlorophylls

Question 21

What is the purpose of accessory pigments? Name two types

Answer 21

• To collect other wavelengths of light and deliver the energy to the primary light harvesting pigments
• To protect the organism from intense sunlight, which could damage the photosynthetic apparatus by over oxidising it
• carotenoids and phycobiliproteins

Question 22

carotenoid

Answer 22

An accessory pigment in the photosynthetic apparatus. Accessory pigments:

• Collect other wavelengths of light and deliver the energy to the primary light harvesting pigments
• Protect the organism from intense sunlight, which could damage the photosynthetic apparatus by over oxidising it

Question 23

phycobiliprotein

Answer 23

An accessory pigment in the photosynthetic apparatus. Accessory pigments:

• Collect other wavelengths of light and deliver the energy to the primary light harvesting pigments
• Protect the organism from intense sunlight, which could damage the photosynthetic apparatus by over oxidising it

Question 24

What two groups of bacteria metabolise forms of inorganic sulfur during their photosynthetic process?

Answer 24

Green sulfur bacteria and Purple sulfur bacteria. The names are derived from the appearance of their pigments

Question 25

Which group of sulfur utilising bacteria include forms in which an organic compound replaces sulfur in their photosynthesis?

Answer 25

The **purple sulfur bacteria** also have members that use organics instead of sulfur, these are termed **purple nonsulfur bacteria**

Question 26

Aside from the use of sulfur, what is the main difference between the photosynthetic sulfur and nonsulfur bactera?

Answer 26

Green and purple sulfur bacter are **obligate anaerobes** (they cannot tolerate oxygen), while purple nonsulfur bacteria are **facultative anaerobes** (can grow without oxygen but grow better in its presence)

Question 27

In what enviornment are the photosynthetic sulfur and nonsulfur bacteria found?

Answer 27

Both are found in aquatic sediments exposed to light

Question 28

What purple nonsulfur bacteria was oberved in Demo 7C?

Answer 28

*Rhodospirillum rubrum* Viewed under dark-field microscopy Dark field microscopy is a very simple yet effective technique and well suited for uses involving live and unstained biological samples, such as a smear from a tissue culture or individual, water-borne, single-celled organisms. Considering the simplicity of the setup, the quality of images obtained from this technique is impressive. The main limitation of dark field microscopy is the low light levels seen in the final image. This means the sample must be very strongly illuminated, which can cause damage to the sample. Dark field microscopy techniques are almost entirely free of artifacts, due to the nature of the process. However, the interpretation of dark field images must be done with great care, as common dark features of bright field microscopy images may be invisible, and vice versa. While the dark field image may first appear to be a negative of the bright field image, different effects are visible in each. In bright field microscopy, features are visible where either a shadow is cast on the surface by the incident light, or a part of the surface is less reflective, possibly by the presence of pits or scratches. Raised features that are too smooth to cast shadows will not appear in bright field images, but the light that reflects off the sides of the feature will be visible in the dark field images.

Question 29

*Rhodospirillum rubrum*

Answer 29

Purple nonsulfur bacteria, viewed under dark-field microscopy in Demo 7C

Question 30

Cyanobacteria

Answer 30

Example from Demo 7C: *Anabaena* Formerly known as blue-green algae, they are Gram-negative Cyanobacteria are a group of photosynthetic, nitrogen fixing bacteria that live in a wide variety of habitats such as moist soils and in water. They may be free-living or form symbiotic relationships with plants or with lichen-forming fungi as in the lichen genus Peltigera.[12] They range from unicellular to filamentous and include colonial species. Colonies may form filaments, sheets, or even hollow balls. Some filamentous species show the ability to differentiate into several different cell types: vegetative cells, the normal, photosynthetic cells that are formed under favorable growing conditions; akinetes, climate-resistant spores that may form when environmental conditions become harsh; and thick-walled heterocysts, which contain the enzyme nitrogenase, vital for nitrogen fixation.

Question 31

Winogradsky Column

Answer 31

The Winogradsky column is a simple device for culturing a large diversity of microorganisms. - Invented in the 1880s by Sergei Winogradsky - A column of pond mud and water mixed with a carbon source - Incubating the column in sunlight for months results in an **aerobic/anaerobicgradient gradient** as well as a **sulfide gradient**. These two gradients promote the growth of different microorganisms

Question 32

What two gradients are present in a Winogradsky column?

Answer 32

An oxygen gradient (high on top to low on bottom), a sulfide (S^2-) gradient (more oxidised on top to more reduced (H₂S) on bottom), and a methane gradient (more CH₄ on bottom)

Question 33

When a Winogradsky column is first set up, what is the oxygen availability like?

Answer 33

The entire column is aerobic

Question 34

What is the initial carbon source of the Winogradsky column? The sulfer source?

Answer 34

CaCO₃ (**calcium** **carbonate**) is the carbon source, CaSO₄ (**calcium** **sulfate**) and **egg** **yolk** serve as the sulfur sources

Question 35

Describe the four-step sequence of events in a Winogradsky column

Answer 35

1) Heterotrophic microbes oxidise some of the organic matter and consume O₂, making lower parts of the column anaerobic **Organic matter + O₂ -\> Organic acids + CO₂** 2) The organic acids act as electron donors for reduction of sulfates and sulfites to hydrogen sulfide (H₂S) by anaerobic sulfate-reducing bacteria **Organic acids + SO4 -\> H₂S + CO₂** 3) Photosynthetic organisms such as purple and green sulfur bacteria (*Chromatium* and *Chlorobium*) use H₂S as an electron donor to reduce CO₂ directly into carbohydrates for use by bacteria **CO₂ + H₂S -(light)-\> carbohydrate + S** 4) Once H₂S level is lowered, another photosynthetic group, the purple non-sulfur bacteria (*Rhodospirillum*, *Rhodopseudomonas*, *Rhodomicrobium*) appear. They use low levels of H₂S as an electron donor to reduce CO₂ into carbohydrates **CO₂ + H₂S -(light)-\> carbohydrate + S**

Question 36

Where do heterotrophic bacteria grow in a Winogradsky column?

Answer 36

Throughout, in both aerobic and anaerobic zones

Question 37

When do purple non-sulfur bacteria appear in the Winogradsky column?

Answer 37

They appear early in the upper portion (where H₂S concentrations are low) in a rust coloured belt, then later in the anaerobic lower portion after purple and green sulfur bacteria convert high levels of H₂S to lower levels by using it as an electron donor for CO₂ reduction to carbohydrates

Question 38

List two lactate-utilising organisms

Answer 38

*Propionibacterium*, *Veillonella*

Question 39

repressive selection

Answer 39

Uses selective media to repress the growth of interfering microbes at the same time permitting the growth of the culture sought

Question 40

enrichment selection

Answer 40

encourage the growth of the sought-after microbe so it will outstrip its competitors

Question 41

differential plating

Answer 41

Using an enrichment media that makes a desired culture easier to recognise compared to others

Question 42

How could a buffer interfere with a differential plating?

Answer 42

The buffer may prevent the change in media that would be seen due to presence of the desired organism Ex a high concentration of buffer could mask acid production from fermentation

Question 43

Where could one find *Streptococcus lactis* in nature?

Answer 43

Soured raw milk

Question 44

Where could one find *Propionibactrium* in nature?

Answer 44

Swiss cheese

Question 45

Where could one find *Acetobacter* in nature?

Answer 45

Unpasteurised draught beer or fruits

Question 46

Where could one find *Enterococcus faecalis* in nature?

Answer 46

Feces

Question 47

Where could one find *Leuconostoc* in nature?

Answer 47

Cabbage leaves

Question 48

When can you assume you have a pure culture?

Answer 48

When a plated sample contains only _one_ colony type

Question 49

*Escherichia coli* habitat, features, medium

Answer 49

Habitat: lower intestinal tract Features: Gram-negative rod, motile, no endospores, mixed acid fermentation Medium: MacConkey's plate (MAC), Tryptic soy agar plate

Question 50

*Enterococcus faecalis* habitat, features, medium

Answer 50

Habitat: lower intestinal tract Features: Gram-positive cocci, non-motile, no endospores, non-haemolytic Medium: Colisin-Nalidixic acid agar (CNA)

Question 51

*Staphylococcus* habitat, features, medium

Answer 51

Habitat: Mammaliam skin, also sand, water plants, food and dust Features: Gram-positive cocci, non-motile, no endospores Medium: Blood agar plate (BAP)

Question 52

*Bacillus* habitat, features, medium

Answer 52

Habitat: Soil Features: Gram-positve rods, motile, endospores Medium: Tryptic soy agar plate

Question 53

*Pseudomonas* habitat, features, medium

Answer 53

Habitat: Soil Features: Gram-negative rods, motil, no endospores Medium: p-hydroxybenzoate enrichment medium