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Flashcards in Quiz 3 Web-Only Deck (54)
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1
Q

What species produces a carcinogenic compound called aflatoxins? Aspergillus flavus

A

Aspergillus flavus

2
Q

Aspergillus flavus

A

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

3
Q

Aflatoxin

A

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

4
Q

Myxobacteria

A

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.

5
Q

gliding motility

A

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

6
Q

Example of myxobacteria and life cycle

A

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).

7
Q

Life cycle of Myxococcus xanthus

A

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).

8
Q

fruiting bodies

A

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

9
Q

myxospore

A

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.

10
Q

sporangiole

A

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

11
Q

What bacteria was observed on rabbit dung in experiment 7?

A

Myxococcus xanthus

12
Q

Actinomycetes

A

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

13
Q

Two types of mycelia in Actinomycetes

A

–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

14
Q

conidiospores

A
15
Q

Streptomyces

A

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

16
Q

TTC Deep

A

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)
17
Q

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

A

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.

18
Q

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

A

Over half of all photosynthesis on Earth

19
Q

What microbes are responsible for photosynthesis?

A

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

20
Q

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

A
  • 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
21
Q

What is the purpose of accessory pigments? Name two types

A
  • 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
22
Q

carotenoid

A

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
23
Q

phycobiliprotein

A

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
24
Q

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

A

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

25
Q

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

A

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

26
Q

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

A

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)

27
Q

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

A

Both are found in aquatic sediments exposed to light

28
Q

What purple nonsulfur bacteria was oberved in Demo 7C?

A

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.

29
Q

Rhodospirillum rubrum

A

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

30
Q

Cyanobacteria

A

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.

31
Q

Winogradsky Column

A

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
32
Q

What two gradients are present in a Winogradsky column?

A

An oxygen gradient (high on top to low on bottom), a sulfide (S2-) gradient (more oxidised on top to more reduced (H2S) on bottom), and a methane gradient (more CH4 on bottom)

33
Q

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

A

The entire column is aerobic

34
Q

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

A

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

35
Q

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

A

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

36
Q

Where do heterotrophic bacteria grow in a Winogradsky column?

A

Throughout, in both aerobic and anaerobic zones

37
Q

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

A

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

38
Q

List two lactate-utilising organisms

A

Propionibacterium, Veillonella

39
Q

repressive selection

A

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

40
Q

enrichment selection

A

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

41
Q

differential plating

A

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

42
Q

How could a buffer interfere with a differential plating?

A

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

43
Q

Where could one find Streptococcus lactis in nature?

A

Soured raw milk

44
Q

Where could one find Propionibactrium in nature?

A

Swiss cheese

45
Q

Where could one find Acetobacter in nature?

A

Unpasteurised draught beer or fruits

46
Q

Where could one find Enterococcus faecalis in nature?

A

Feces

47
Q

Where could one find Leuconostoc in nature?

A

Cabbage leaves

48
Q

When can you assume you have a pure culture?

A

When a plated sample contains only one colony type

49
Q

Escherichia coli habitat, features, medium

A

Habitat: lower intestinal tract

Features: Gram-negative rod, motile, no endospores, mixed acid fermentation

Medium: MacConkey’s plate (MAC), Tryptic soy agar plate

50
Q

Enterococcus faecalis habitat, features, medium

A

Habitat: lower intestinal tract

Features: Gram-positive cocci, non-motile, no endospores, non-haemolytic

Medium: Colisin-Nalidixic acid agar (CNA)

51
Q

Staphylococcus habitat, features, medium

A

Habitat: Mammaliam skin, also sand, water plants, food and dust

Features: Gram-positive cocci, non-motile, no endospores

Medium: Blood agar plate (BAP)

52
Q

Bacillus habitat, features, medium

A

Habitat: Soil

Features: Gram-positve rods, motile, endospores

Medium: Tryptic soy agar plate

53
Q

Pseudomonas habitat, features, medium

A

Habitat: Soil

Features: Gram-negative rods, motil, no endospores

Medium: p-hydroxybenzoate enrichment medium

54
Q
A