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
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
