Biology
Updated: 2008-07-02
Please send comments to: J.Elfick@uq.edu.au
9.196 Rhizopus nigricans, mouldy bread,
Phylum Zygomycota
See diagram 9.196: Rhizopus, | Rhizopus nigricans,
bread mould | See diagram 9.19.1:
Rhizopus oryzae
Rhizopus genus have stolons, pigmented rhizoids, with
sporangiophores from nodes above the rhizoids, dense white to brown
cotton-like growth
Rhizopus nigricans, bread mould, stolonifer black bread mould
Rhizopus oryzae, R. arrhizuz) fermentation of foods,
Japanese sake
1. Mount a small fragment of mould from old bread or decaying fruit and
examine under the low power. Note the
filaments that are the vegetative body of this fungus.
2. Invert a smaller flat
transparent dish in the bottom of a larger flat transparent dish.
Stand a piece of bread on the small dish. Add tap water to the large
dish until it is half way up the side of the small dish. Cover the
larger dish with its lid and leave the assembly to stand at room
temperature. Under these moist chamber conditions, off-white, furry
masses of mould (Mucoraceen and Aspergillacae) develop
after a few days on the bread. Later these form grey-black or green
sporophores.
9.197 Phytophthora infestans, Phylum
Heterokontophyta
potato blight, die back, root rot, cocoa black pod
This fungus caused the potato famine in Ireland 1845.
Examine the leaf of a potato plant infected with potato blight. Look
for the lighter patches, or if the disease is advanced they will appear
dark brown, where the leaf is attacked by the fungus. Obtain a prepared
microscope slide of a section of an infected leaf and observe
dark blotches on leaf tips and white mould under the leaves. Study
prepared slides showing the
method of
reproduction.
9.198 Pythium, root rot, damping-off
fungus, Phylum Oomycota
Pythium blight, cottony blight is a fungal disease of grass,
especially turf grass and greenhouse seedlings. It causes small patches
of blighted grass with
shrivelled leaves during warm, wet periods. Observe Pythium
under the low and high
powers. Study prepared slides of the asexual and sexual methods of
reproduction.
9.199 Mucor, Phylum Zygomycota, cheese
making
See diagram 9.202
Place some damp bread under a large jar, and leave it for a few days
until it becomes mouldy. Take a small portion of the mouldy bread and
examine the fungus responsible with the high power. Look for
spore-producing bodies of Mucor. Study prepared slides
showing
stages in sexual reproduction. Examine a culture of the two strains (+
and -).
9.200 Eurotium, Phylum Ascomycota
Examine a mycelium of Eurotium under high power. Note the
branched, septate hyphae. Look for conidiophores producing chains of
conidia. Observe perithecia attached to the mycelium by thicker hyphae
of a darker colour. Gently press the coverslip to burst the wall of
sterile hyphae so that the small asci will be extruded. Examine one
ascus and look for the eight ascospores.
9.201 Agaricus, mushroom, Phylum
Basidiomycota
See diagram 9.201: Agaricus
Agaricus bisporus, white
mushrooms, Swiss brown mushroom, edible mushrooms
Examine the reproductive portion of a mushroom. Choose a ripe
fructification and remove the stipe and place the umbrella-shaped part,
the pileus, on a piece of paper with the gills downwards. Leave for a
few days, then gently lift the pileus. See the arrangement of the gills
traced on the paper by thousands of small, black, reproductive
spores that have been shed. Study a prepared slide of the
longitudinal section of a gill to observe its detailed structure and
the means of basidiospore production.
9.202 Penicillium, Penicillin antibiotic,
Phylum
Ascomycota
See diagram 9.202: Penicillium | See diagram 9.202.1: Penicillium with branching
conidiophores | Penicillium, penicillin antibiotic
Penicillium, soil mould
P. purpurogenum (formerly P. rubrum) plant pathogen
P. candida, P. camemberti, P. glaucum, P. roqueforti,
cheese making, P. chysogenum (formerly called P. notatum),
antibiotic penicillin
P. italicum, P. olivaceum, fruit parasites
Different species produce antibiotics, and are
essential for production of certain cheeses, e.g. Roquefort and
Camembert. Antibiotics are excreted by micro-organisms to interfere
with the growth or metabolism of other micro-organisms. In the original
penicillin, the R-group was a mixture and may be varied by adding
molecules to the nutrient solution in which the mould is growing.
Penicillin interferes with the building up of the cell wall of the
cells of Gram positive bacteria.
Gram-positive bacteria appear blue or violet under a microscope from
the crystal violet dye in Gram stain. Gram-negative bacteria appear
pink-red. However, some bacteria have developed
the enzyme penicillinase, that can destroy penicillin.
9.203 Bathroom and kitchen mould
Moulds may grow in the "grout" between bathroom and kitchen tiles. In
Australia these moulds are usually Penicillium, Rhizopus,
Phoma, Phialophora, and Fusarium. They are
mostly
harmless although Phoma may cause allergies. They can be
cleaned off with bleach solutions.
9.204 Yeast
population, bakers' yeast Saccharomyces cerevisiae, Phylum
Ascomycota
See diagram 9.204: Yeast cell forming
bud
The simplest form of asexual reproduction
is budding, in which a protuberance grows out from the parent cell and
finally cutting itself off to become an independent cell. Budding
occurs in yeasts. Natural sources of yeast include the wax-like
coatings on smooth skinned fruits, especially grapes. However, bakers'
yeast is usually obtainable. It reproduces rapidly, making it a good
subject for observing population changes under varying conditions.
1. Set up tubes of sugar, molasses or honey solutions and a water
control. Put a quarter cake of crumbled yeast in each tube. Compare the
results. Put a one-hole stopper with glass tubing in the sugar yeast
solution and allow the gas produced to bubble through a tube of clear
limewater to detect the presence of carbon dioxide. Test the
gas produced by the sugar yeast solution.
2. Fill a test-tube half full
of 10% sugar solution, drop in a piece of bakers' yeast, plug the
test-tube with cotton wool and allow to stand at room
temperature. After 12 to 24 hours, transfer a drop from this culture on
to
a microscope slide using a glass rod, put a coverslip over it and
examine the preparation under a microscope. Look for cells
with protrusions or asexual buds. If you can see
nuclei in the cells, look for their presence in the buds.
9.205 Sampling yeast
populations
1. Start a culture each day for 10 days using one grain of yeast for
each
culture. On the tenth day sample and count all cultures with a
microscope. Use a special slide for counting blood cells, but it is not
essential. If the population on a given day is too large to count,
dilute a sample by adding 1 mL of sample and 9 mL of water. Multiply
the count by 10 to get the actual sample size. If one dilution is not
enough, further dilution may be done until it becomes easy to count the
number of organisms. The multiplication factor for two dilutions is 10
by 10 or 100: for three dilutions it is 10 by 10 by 10 or 1, 000. Note
that each successive dilution is started from part of the previous
dilution, not from the original sample. Graph the data obtained from
cultures for analysis. Time is the independent variable and population
size is the dependent variable.
2. An effective method of studying population growth with
micro-organisms is to start a culture each day and, on the final day,
to sample and count all cultures. For example, a new yeast culture can
be started each day for 10 days, using one grain of yeast for each
culture. On the tenth day samples are taken from each culture and
counted with a microscope. A special slide for counting blood cells is
desirable, but not essential. If the population on a given day is too
large to count, dilute a sample by adding 9 parts water to 1 part of
sample. Use 1 ml of sample and 9 ml of water. Multiply by 10 to get the
actual sample size. If one dilution is not enough, make further
dilutions until it becomes easy to count the number of organisms. The
multiplication factor for two dilutions is 10 by 10 or 100: for three
dilutions it is 10 by 10 by 10 or 1, 000. Note that each successive
dilution is started from part of the previous dilution, not from the
original sample. Graph the data obtained from cultures for analysis
with time as the independent variable and population size is the
dependent variable.
9.206 Find wild yeasts in flowers
See also 4.1.2: Enrichment of wild
yeast strains
Put a few freshly picked flowers of deadnettle, woundwort or
nasturtium, in a beaker. Cover over
with a suitably sized transparent plastic bag and leave the flowers to
stand in this "humidity chamber" at room temperature. After two days
remove some flowers that are already open. Pull off the petals and
squeeze the nectar from the nectaries onto a microscope slide. Put a
coverslip over the nectar and examine it under a microscope. Look
for nectar yeast cells. Note the shape of the
nectar yeast cells and the size of the buds. Compare the nectar yeast
cells
with the bakers' yeast cells. Observe the cross form or star form of
the branching
chains formed by the wild yeasts on budding. Use agar syrup to culture
the yeasts and moulds.
9.207
Lichens
A lichen is the symbiosis of a
fungi and algae. The photosynthetic
partner in the lichen thallus is called a photobiont. Each type of
lichen has a characteristic shape. Crustose lichens form a thin crust.
Foliose
lichens are like leaves.
Fructicose lichens are stalked.
Squamulose (loosely attached thallus) lichens have a primary and a
secondary thallus. The fungi are mainly Ascomycetes. Lichens may be
nitrogen-fixing. Lichens
are found in most places in the world and are very susceptible to air
pollution in the atmosphere. They may be
damaged by sulfur dioxide or other harmful gases, and may die. So
lichens are sensitive plant detectors of air
pollution. The fungi are mainly Ascomycetes. Example of common lichens
include the following: Acarospora, a crustose lichen that forms
a thin crust, Cladonia, cup lichen, reindeer "moss", a
squamulose, loosely attached thallus lichen with a primary and a
secondary thallus, Evernia, oak
moss lichen, Hypogymnia, a foliose
lichens like a leaf, Lobaria, lungwort, a nitrogen-fixing
lichen, Peltigera, dog lichen, a nitrogen-fixing lichen
and herbal medicine, Stricta, a nitrogen-fixing lichen, Usnea,
a fructicose lichen that has a stalk.
1. Examine a specimen of a common lichen. Study a prepared slide
showing a
transverse section of the thallus revealing the presence of alga and
fungus. Look for the penetrating haustoria.
2. Attach 10 lichens on a board. Then put them in three places, e.g.
near a factory, in the central city and far from the factory.
Observe
any change in the lichens after one mouth. Count the percentage of
damaged
lichens. Lichens indicators are used as indicators of air pollution and
species diversity.
9.208 Slide culture
preparation to identify fungi
See diagram 9.208: Simple agar block method
1. To identify many fungi you must observe the conidiophores, i.e. the
specialized hyphae where asexual spores cut off at the ends, and the
way in which spores are produced. This method allows you to study fungi
with little disturbance. Use one agar plate of nutrient agar, e.g.
potato dextrose agar.
2. Use a sterile blade to cut out an agar block, 7 x 7 mm, small
enough to fit under a coverslip.
9. Flip the agar block up onto the surface of the agar plate. Inoculate
the four sides of the agar block with spores or mycelia fragments of
the fungus to be grown.
4. Place a flamed coverslip centrally upon the agar block. Incubate the
plate at 26oC until growth and spore-forming have occurred.
Remove the
coverslip from the agar block.
5. Apply a drop of 95% alcohol as a wetting agent. Gently lower the
coverslip onto a small drop of lactophenol cotton blue on a clean
glass
slide. Leave the slide overnight to dry and later seal the edges with a
coat of clear fingernail polish followed by one coat of red coloured
polish.
9.209
Rhizobium in legumes
See also 3.30: Nitrogen-fixing
bacteria | See diagram 9.209: T.S. Root nodule
| See diagram 9.72: Root nodules
Rhizobium bacteria can enter the
roots of legumes and cause lumps, root nodules, where they live. These
bacteria can use the
nitrogen
gas from the air. We say Rhizobium
can "fix" nitrogen from the
air. Very few other living things can fix nitrogen. Some nitrogen goes
into the stems and leaves of the legume plant. When
the leaves fall off, some nitrogen compounds are added to the soil that
other
plants can then use. When the
legume plants die, the nitrogen
fixed by the Rhizobium
can still be available to other plants. Some legumes, e.g. cowpea
and lablab bean, are grown until the
flowering stage and then dug into the soil as "green manure".
When these plants rot, they leave nitrogen compounds in the soil both
from
the leaves and root nodules. Different crop plants require different
strains of Rhizobium. Farmers can purchase commercial innoculum
containing the strain appropriate for nodulation of their particular
crop. Dig up different legume plants and count the number of nodules
and note the sizes of the nodules. Cut open some nodules. The inside
of a nodule that is fixing nitrogen is a pink-red colour.
Inactive nodules are brown or green inside.
9.210 Grass in water
Put dead grass or fresh hay in a jar, cover with water and leave it
uncovered to stand at room temperature for some days. Do not use mouldy
hay because it may contain pathogenic fungi. After a few days, a skin
forms on the surface of the water, the mould pellicle. After
eight days, use a glass rod to transfer a part of the pellicle and some
fluid to a microscope slide. Spread out the pellicle evenly and apply a
coverslip. Examine the pellicle under the microscope. Observe
rod-shaped or spherical unicellular bacteria. Observe unicellular
organisms moving very rapidly through the field of view, e.g.
Paramecium.
9.211 Teeth scrapings
Put white scrapings from the teeth on a microscope slide.
Examine the scraping under a microscope and look for any bacteria. You
may have
to seek approval to work with samples from the human mouth because
diseases may
spread. Wear
safety glasses and disposable
surgical gloves.
9.212 Ginger beer plant
The Ginger beer
"plant"
is the yeast Saccharomyces florentinus (S. pyriformis)
and the bacterium Lactobacillus hilgardii (Brevibacterium
vermiforme). Add 5g of bakers' yeast to 25 ml of water and 1/2
teaspoon
of ground ginger and sugar. Put in a screw-top jar and add half a
teaspoon of sugar and some ground ginger every day for a week to keep
the fermentation going. Dissolve 50g of sugar in 50 ml of boiling
water. Strain the mixture and add the sugar solution and lemon juice to
the liquid. Ginger
beer soft drink is made from ginger powder and does not contain
alcohol.
9.213
Viruses
See also 10.9.0: Sexually
transmitted infections, STIs,
HIV and AIDS
A virus is a strand or strand
of nucleic acid covered by protein
and sometimes a membrane. Viruses cause infected cells to produce
progeny viruses. Retroviruses use the enzyme reverse transcriptase to
copy the viral RNA (ribonucleic acid) into DNA (deoxyribonucleic
acid). Plant viruses can usually be
recognized by marks on leaves, e.g. mosaics, leaf streaks, and ring
spots. Viruses are not affected by antibiotics. A bacteriophage is
similar to a very small virus. It infects bacteria.
The classification of
viruses can be based on the type and arrangement of the genetic
material.
Group 1. dsDNA Double-stranded DNA viruses include oral herpes, genital
herpes, chickenpox viruses, cold sore, Herpes simplex virus, types 1
and 2, HSV-1 and
HSV-2, Adenoviruses human adenoids, tonsils, Human
Papilloma Virus, HPV causes genital warts Condylomata acuminata,
Molluscum
Contagiosum Virus
Group 2. ssDNA Single-stranded DNA viruses include some of the
smallest
viruses.
Group 9. dsRNA Double-stranded RNA include viruses responsible for
diarrhoea
in
children.
Group 4. positive sense ssRNA Single-stranded RNA viruses
include influenza, hepatitis A virus, hepatitis C virus, HCV
severe acute respiratory syndrome SARS, foot-and-mouth
disease, yellow fever, rubella viruses and most plant viruses
Group 5. negative sense ssRNA Single-stranded RNA viruses
include
influenza, measles, mumps, rabies, Ebola virus, foot-and-mouth disease
Group 6. ssRNA Diploid single-stranded RNA viruses that use reverse
transcriptase, retroviruses, include HIV virus.
Group 7. ds DNA-RT Circular
double-stranded DNA viruses that use reverse
transcriptase, include hepatitis B Virus, HBV
Human Immunodeficiency Virus, HIV, and
AIDS, acquired
immune deficiency syndrome
9.213.1 HSV-1 and HSV-2
HSV-1, herpes simplex virus causes cold sores, painful blemishes of the
mouth. It can become dormant for years, when drugs cannot affect it,
then, years later, be revived by excessive sunlight or fever to cause a
cold sore in the same place as before.
HSV-2 causes painful genital sores and chicken pox virus that can
return late in life as shingles.
9.214 Aspergillus
See diagram: 9.203: Conidial head
Aspergillus flavus produces an aflotoxin, common soil
saprophyte, pathogen of humans and animals
Aspergillus niger, black mould on food, common infection outside
ear drum, common laboratory contaminant
Aspergillus oryzae
9.215
Candida (formerly Torulopsis)
Candida genus has yeast-like cells, blastoconidia, that
reproduce by budding. All members of the genus occur naturally on
humans. Candida albicans, forms cream coloured, smooth
surface waxy colonies on an agar plate. It
is a commensal of the gastrointestinal tract. However it may cause
candidiasis (candidosis), a common yeast infection, especially of the
vagina, where it is called thrush. Candida tropicalis
is part of the normal mucocutaneous flora but may cause causes
septicaemia and candidiasis. It has been isolated from polluted water,
soil, and air contaminated by human excreta.
Candida albicans commensal on mucous membranes and
gastrointestinal tract, pathogenic, causes thrush (candidosis)
Candida glabrata common yeast species on human body surface,
pathogenic
9.216 Cryptococcus
C. gattii causes mass lesions in the lung and
brain. C. neoformans causes
fungal meningitis.
9.217 Fusarium
Most Fusarium species are soil fungi. Some are plant pathogens
causing
stem rot, root root and fruit rot.
F.
oxysporum causes Panama disease of bananas, fusarium wilt and
dangerous infections in human burns victims.
F. graminearum infects barley
9.218 Microsporum
M. audouinii and M. ferrugineum
cause non-inflammatory infections of the scalp, tinea capitis,
especially in children.
M. canis causes ringworm,
especially in children. The infection comes from cats and dogs.
M. gallinae causes "white
comb" lesions in chickens.
M. nanum causes chronic
non-inflammatory lesions in pigs. Infected pigs may infect
humans.
9.219 Trichophyton, ringworm
disease
Many strains of Trichophyton
as medical fungi exist but they
are generally classified as T. rubrum,
downy type, and T. rubrum
granular type. The downy type have slender microconidia and no
macroconidia. They cause chronic infection of the skin and nails. The
granular type have
microconidia and cigar-shaped macroconidia. They cause tinea corporis
in South-East Asian and in aborigines in Northern Australia. Also, it
causes tinea pedis, athlete's foot, in feet in Europe and North
America, favus, a chronic scarring form of tinea capitus, a type of
ringworm of the scalp, and dhobie itch, tinea cruris, that affects the
groin and nearby regions. Some strains can invade human hairs and cause
the "black dot" tinea capitis.
9.220 Puccinia
Wheat rust, white pine blister rust, apple cedar rust, hollyhock rust,
asparagus rust