Quiz 3 Web-Only Flashcards
What species produces a carcinogenic compound called aflatoxins? Aspergillus flavus
Aspergillus flavus
Aspergillus flavus
A fungi that produces carcinogenic compounds called aflatoxins, flat-ringed planar compounds that can intercalate between bases of DNA and act as mutagens.
Aflatoxin
Flat-ringed planar compounds produced by the fungus Aspergillus flavus that can intercalate between bases of DNA and act as mutagens.
Myxobacteria
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.
gliding motility
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
Example of myxobacteria and life cycle
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).
Life cycle of Myxococcus xanthus
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).
fruiting bodies
Multicellular aggregates of Myxococcus xanthus that form vegetative cells when nutrients are low. Contain differentiated cells called myxospores that are stress-tolerant.
myxospore
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.
sporangiole
In some genera of Myxococcus xanthus, myxospores are contained in sacs called sporangioles
What bacteria was observed on rabbit dung in experiment 7?
Myxococcus xanthus
Actinomycetes
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
Two types of mycelia in Actinomycetes
–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
conidiospores
Streptomyces
Of phylum Actinomycetes, Streptomyces produces 10,000 compounds including antibiotics, responsible for the smell of soil
TTC Deep
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)
What kind of plate, used in Demo 7B, selectively favours Actinomycetes?
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.
What proportion of photosynthesis is estimated to be carried out by microbes?
Over half of all photosynthesis on Earth
What microbes are responsible for photosynthesis?
The Cyanobacteria (formerly known as Blue/Green algae) and Green and Purple bacteria
What is the difference between the photosynthetic processes in Cyanobacteria and Green and Purple bacteria?
- 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
What is the purpose of accessory pigments? Name two types
- 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
carotenoid
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
phycobiliprotein
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
What two groups of bacteria metabolise forms of inorganic sulfur during their photosynthetic process?
Green sulfur bacteria and Purple sulfur bacteria. The names are derived from the appearance of their pigments
Which group of sulfur utilising bacteria include forms in which an organic compound replaces sulfur in their photosynthesis?
The purple sulfur bacteria also have members that use organics instead of sulfur, these are termed purple nonsulfur bacteria
Aside from the use of sulfur, what is the main difference between the photosynthetic sulfur and nonsulfur bactera?
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)
In what enviornment are the photosynthetic sulfur and nonsulfur bacteria found?
Both are found in aquatic sediments exposed to light
What purple nonsulfur bacteria was oberved in Demo 7C?
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.
Rhodospirillum rubrum
Purple nonsulfur bacteria, viewed under dark-field microscopy in Demo 7C
Cyanobacteria
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.
Winogradsky Column
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
What two gradients are present in a Winogradsky column?
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)
When a Winogradsky column is first set up, what is the oxygen availability like?
The entire column is aerobic
What is the initial carbon source of the Winogradsky column? The sulfer source?
CaCO3 (calcium carbonate) is the carbon source, CaSO4 (calcium sulfate) and egg yolk serve as the sulfur sources
Describe the four-step sequence of events in a Winogradsky column
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
Where do heterotrophic bacteria grow in a Winogradsky column?
Throughout, in both aerobic and anaerobic zones
When do purple non-sulfur bacteria appear in the Winogradsky column?
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
List two lactate-utilising organisms
Propionibacterium, Veillonella
repressive selection
Uses selective media to repress the growth of interfering microbes at the same time permitting the growth of the culture sought
enrichment selection
encourage the growth of the sought-after microbe so it will outstrip its competitors
differential plating
Using an enrichment media that makes a desired culture easier to recognise compared to others
How could a buffer interfere with a differential plating?
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
Where could one find Streptococcus lactis in nature?
Soured raw milk
Where could one find Propionibactrium in nature?
Swiss cheese
Where could one find Acetobacter in nature?
Unpasteurised draught beer or fruits
Where could one find Enterococcus faecalis in nature?
Feces
Where could one find Leuconostoc in nature?
Cabbage leaves
When can you assume you have a pure culture?
When a plated sample contains only one colony type
Escherichia coli habitat, features, medium
Habitat: lower intestinal tract
Features: Gram-negative rod, motile, no endospores, mixed acid fermentation
Medium: MacConkey’s plate (MAC), Tryptic soy agar plate
Enterococcus faecalis habitat, features, medium
Habitat: lower intestinal tract
Features: Gram-positive cocci, non-motile, no endospores, non-haemolytic
Medium: Colisin-Nalidixic acid agar (CNA)
Staphylococcus habitat, features, medium
Habitat: Mammaliam skin, also sand, water plants, food and dust
Features: Gram-positive cocci, non-motile, no endospores
Medium: Blood agar plate (BAP)
Bacillus habitat, features, medium
Habitat: Soil
Features: Gram-positve rods, motile, endospores
Medium: Tryptic soy agar plate
Pseudomonas habitat, features, medium
Habitat: Soil
Features: Gram-negative rods, motil, no endospores
Medium: p-hydroxybenzoate enrichment medium
