Week 3, Viruses, classification, and ID

Question 1

Describe the binomial nomenclature system.

Answer 1

Names consist of two parts: the genus, which can be shortened to the first letter of the genus, followed by the species; e.g. Bacillus subtilis = B. subtilis

Question 2

Define what a prion is.

Answer 2

Infectious misfolded proteins devoid of nucleic acids that cause disease in vertebrates and fungi.

Question 3

How are viruses classified?

Answer 3

→ Shape of virion (round, rod, etc)
→ Host
→ Genome properties (DNA/RNA, sense, etc)

Question 4

Describe some morphological features of the Rhizopus species

Answer 4

→ Pin moulds common in soil and decaying organic matter
→ Form mould on bread and soft rot in fruit and veg
→ Large, dark-coloured sporangia visible to the naked eye
→ Non-motile spores
→ Root-like rhizoids are present at the base of the hypha that bears a sporangium (this features helps distinguish it from Mucor species)
→ The sporangium has a distinctive cullumella (swollen septum at the apex of the hypha that bears the sporangium)

Question 5

What morphological characteristics of fungi should be recorded for identification?

Answer 5

→ Size
→ Hyphae (septate/aseptate)
→ Spores
→ Spore-bearing structures

Question 6

What are different species classified based on?

Answer 6

→ Morphology
→ Other growth-dependent methods (physiology, metabolic tests, chemical composition, etc)
→ Molecular biology

Question 7

Describe some features of the Botrytis species

Answer 7

→ Cause grey mould of fruits, vegetables, and ornamentals; and bunch rot or noble rot in grapes, depending on the environment
→ Sectoring is common in culture
→ Sclerotia may be formed in old cultures
→ Long, branching, olive-grey, aerial conidiophores with swolen apical cells that are covered with ovoid conidia borne on short projections

Question 8

What is the difference between a species, a strain, and a type strain?

Answer 8

SPECIES:
→ A collection of strains that exibit many common characteristics and which differ from other strains.

STRAIN:
→ Descendants of a single cell/isolate (clones).

TYPE STRAIN:
→ A reference specimen that typifies the species.

Question 9

What is the difference between lytic and lysogenic viruses?

Answer 9

LYTIC: virus kills infected cell
LYSOGENIC: virus genome is integrated into host genome (infection remains latent)

Question 10

Describe some features of the Penicillium species

Answer 10

→ Food spoilage, plant diseases
→ Some produce mycotoxins
→ Form dense, powdery colonies
→ Typically grey, green, or bluish, with a white margin where conidia haven’t formed yet
→ Characteristic brush-like conidiophore (the penicillus) with chains of conidia
→ Species can be distinguished based on the morphology of the penicillus and the size, shape, and colour of the spores.

Question 11

What scale range are viruses found in?

Answer 11

20-300 nm
longest = 2000 nm

Multiple shapes.

Question 12

How do viruses multiply?

Answer 12

1. Virions enter the cytoplasm of a living cell
2. Virus genes expressed in host cell
3. New virions assemble from viral RNA/DNA and protein
4. Virions escape the cell and infect new cells
5. Infected host cells show disease

Question 13

Define what a virus is.

Answer 13

A set of one or more genomic nucleic acid molecules, normally encased in a coat/s of protein or lipoprotein, that is able to replicate itself within suitable host cells.

Question 14

T/F: Viruses only affect vertebrates, invertebrates, plants, and fungi

Answer 14

False. They also infect bacteria, algae, and protozoa. That said, each virus has individual host-specificity.

Question 15

What is the difference between classification and identification?

Answer 15

CLASSIFICATION:
→ Arranging organisms into taxonomic groups based on similarities or relationships

IDENTIFICATION:
→ Determining that a new isolate belongs to an established taxonomic group

Question 16

Explain the difference between vertical and horizontal virus transmission.

Answer 16

HORIZONTAL:
→ Between individual hosts of the same generation
     - aerosols
     - ingestion
     - contact
     - tissue transfer
     - vector (e.g. mosquito)

VERTICAL:
→ From parent to offspring
     - milk
     - placenta
     - seed
     - integrated into parent genome

Question 17

T/F: Viruses replicate in living cells only.

Answer 17

True.

Question 18

Describe some features of the Alternaria species

Answer 18

→ Common pathogens of aerial plant parts, often causing leaf and pod spots
→ Dark gray/black colonies
→ Often form concentric zone lines (dark areas where conidia are dense)
→ Characteristic large, multicellular, darkly coloured conidia borne on simple, pigmented conidiophores.
→ Best viewed without stain (lactoglycerol only)

Question 19

Define what a viroid is.

Answer 19

Small, circular RNA molecules that can infect PLANT CELLS, replicate themselves, and cause PLANT disease.

Question 20

Describe the structure (size, shape, stability) of viruses.

Answer 20

SIZE: Generally 20-300 nm in diameter
SHAPE: sphere, rod, bullet, lemon, tailed
STABILITY: varying sensitivity to temp, pH, salt, radiation, desiccation, enzymes, etc