Introduction to Microbiology Flashcards
overview of earth formation
- 4.5Gy = supernova created the sun and planets
- 4.0Gy = apparition of water and atmosphere
- 3.9Gy = earth cooled down and water condensed to form oceans
- oldest sedimentary rocks formed
- 3.5Gy = stromatolites were formed
- bacterial communities lived in sediment layers
- Microfossils
- first experimental evidence that life started around 3.5Gy
what is the prebiotic soup model?
This model suggests that the chemically reducing atmosphere of the earth produced simple organic monomers. These monomers accumulated in a ‘soup’, producing complex polymers, and eventually life
all building blocks of life can be produced from the same pool of compounds under certain conditions;
- hydrogen cyanide (HCN)
- hydrogen sulphide (H2S)
What was Miller’s experiment?
An atmosphere that mimicked the atmosphere of early earth was produced by mixing water vapour, methane, molecular hydrogen and ammonia with electrical discharges.
A week later, organic compounds like amino acids were produced
limitations: no evidence of amino acids present in sediments, and the atmosphere had a higher H2 concentration than what was used in the experiment
what is the RNA world hypothesis
RNA could have been the first macromolecule encoding complex info:
- requires less energy than DNA to form/degrade as unwinding isnt required
- some viruses use ssRNA as genetic material
- RNA have have catalytic properties - ribozymes = splicing
How did compartmentalisation lead to LUCA? (apparition of cellular life)
Hypothesis 1: surface origin
- primitive cells were formed spontaneously on earth from prebiotic soup
- natural selection led to optimise metabolic process
Hypothesis 2: subsurface origin
- life appeared in hydrothermal mounds on ocean floor
- geothermally heated water from fissure, and cool ocean water formed montmorillonite clays
- H2 and H2S provided electrons to form organic molecules
what is the panspermia theory?
life originated from space and that evolution is driven by viruses from space e.g. spanish flu
who introduced the nomenclature for the 3 domains of life?
Carl Woese: he intoduced Bacteria, Archaea and Eukarya, defining a new taxon
How does gene plasticity cause microbial diversity?
Haploid genome creates diversity:
- bacteria only have one chromosome, so mutations are easily passed on
Rapid multiplication means population can double within 20 minutes
- 10 hours -> 1 billion cells
Gene transfer: transformation, transduction, conjugation
what is taxonomy?
discipline which deals with classification of organisms
- species are defined according to a taxonomic hierarchy + common phenotypes
- uses binomial nomenclature
Describe phenotypic analyses used in taxonomy:
- morphology/staining
- direct observations
- limited as morphology can change depending on environment - metabolic properties
- biochemical tests on unknown bacteria produce an ID value after incubation which can be compared to a computerised list to identify the bacteria - phage typing
- phages identify species by targeting specific organisms on agar plate
- lysis plaques are zones of bacteria which have been lysed by phages - fatty acid profiles
- fatty acids are extracted from bacterial culture and gas chromatography forms peaks which can be compared on database - mass spectrometry
- surface proteins produce a finger print of molecules associated with that organism which can be compared on database
describe genotypic analyses used in taxonomy:
- DNA hybridisation
- comparision of 2 species by seeing hoe much their DNA can hybridise by denaturing them and mixing them together
- no. H bonds formed indicates how closely they are related - FISH
- gene is labelled and hybridised with DNA in sample, and can see which organisms have that gene - MLST/fingerprinting
- housekeeping genes are selected and sequenced to compare alleles of different genes
- barcode is formed which can be compared with other species - whole genome sequencing
- samples are prepared and sent to a company
what is phylogeny?
studies evolutionary history and relationships of organisms
- achieved by comparing DNA and using rRNA sequences called molecular clocks
- housekeeping genes are required across many organisms for comparison
- forms phylogenetic trees which is based on a comparative analysis of the rRNA gene sequence
name some unicellular eukaryotes:
Fungi: - yeasts = unicellular - molds = filamentous - basidiomycetes = mushrooms can be multicellular
protists:
- unicellular algae (plant-like)
- protozoa (animal-like)
- slime molds
General properties of fungi:
- cell walls made of chitin, mannans and/or glucans
- most form multicellular filaments called hyphae (pleiomorphic)
- 2 phases in life cycle involving asexual and sexual reproduction to form spores (resistant)
- undergo transitions between unicellular and multicellular forms
why are fungi important?
- contribute to carbon cycle as they are decomposers
- can be plant pathogens and spoil 10-30% of crops
- loss of £150 billion/year
- penicillin is extracted from mold
- fungal infections cause over 1.5 million deaths per year
what are molds?
filamentous fungi e.g. bread mold
- vegetative form = coenocytic hyphae
- absorption and nutrient growth occur at tip of hyphae which secretes material via vesicles
- hyphae drive symbiosis and pathogenesis
what are basidiomycetes and their life cycle?
- live in symbiosis with plants/trees
- form huge mycelium networks in association with roots of trees
- provide plant with nutrients in return for amino acids
life cycle:
- haploid mycelium undergoes cytoplasmic fusion to form secondary mycelium
- gametes fuse nuclei to form diploid zygote
what are yeasts?
- unicellular fungi
- used in brewery and bakery industries (S. cerevisiae)
- cause opportunisitic infections of humans (crytpococcus and candida)
- used as a model organism for apoptosis, cell cycle, mitochondira and oxidative stress, lysosomal/peroxisomal function and vesicular trafficking
what is the life cycle of yeast?
- multiplies by budding or asymmetric binary fission
- cell expands to form progeny cell (bud scar is left)
- form unicellular but become hyphae under specific conditions (dimorphism)
- haploids germinate and multiply in mitosis to form new progeny
- haploids mate and fuse genetic material to form diploids which multiply by mitosis
- diploid phase forms sporangium which produce spores to start cycle again
what are the two types of unicellular algae?
primary endosymbiotic algae (Chlamydomonas reinhardtii):
- autotrophs
- match structure of chloroplasts
- true algae resulting from ancestral endosymbiosis
secondary endosymbiotic algae (diatoms):
- result from protists that engulfed primary endosymbiont
- mixotrophs
- structure of chloroplasts have extra set of membranes (2 engulfments occured)
- envelope with 4 different membranes
- nucleus is engulfed and degenerates
why are unicellular algae important?
- components of phytoplankton so produce 50-80% of atmos oxygen
-key food item in ocean food web - model organism:
- photosynthesis, motility, cell cycle
oxidative stress etc - doubling time 6-8 hours
- swims using 2 flagella
- contains chloroplast with 2
membranes - vacuole for osmoregulation
- cell wall made of hydroxyproline
glycoproteins (NO CELLULOSE)
- photosynthesis, motility, cell cycle
what is the life cycle of unicellular algae?
- haploid asexual reproduction (binary fission)
- meiosis to form gametes
- haploid cells form opposite mating types that fuse to form zygote
colonial life style:
- colonies within colonies made of linked cells with shared cytoplasm
- contains specialised cells which undergo sexual/asexual cycle
what are diatoms?
- mot abundant organisms in phytoplankton
- produces 20% of the oxygen on earth
- large morphological diversity
- mobile by sliding on mucus using actin and myosin (don’t use appendeges)
- mixotrophs: photosynthesis and metabolism (not just reliant on one process)
- chloroplasts have 4 membranes
- cell wall called frustule , which is made of silica (crosslinked silicon oxide)
have treatments against fleas/red mites
what are the two types of diatoms?
- radial symmetry = centric diatoms
2. bilateral symmetry = pennate diatoms
what is the life cycle of diatoms?
- frustules sediment at bottom of ocean
- cell walls are rigid, so division is unusual
- frustules have 2 valves, with one overlapping the other
- each daughter cell inherits half of the frustule and is smaller than the parent cell
- when critical size is reached, the cell undergoes meiosis to form gametes
- zygote is formed which forms a frustule the same size as the parental diatom
what are coccolithophores?
a form of secondary endosymbiotic algae
their frustules are made of calcium carbonate, meaning they have key role in carbon cycle
what are alveolates (protozoa)?
- contain alveoli
- motile organisms due to cilia
- mainly aquatic
3 types:
- ciliates - predatory protists
- key role in food web (zooplankton) - apicomplexans - parasites
- major impact on human health e.g. malaria parasite
- dinoflagellates - predatory algae
- key role in carbon cycle
what are ciliates?
- contain 2 micronuclei with germline material
- contain a macronucleus with metabolic functions and polyploid genome
- cilia are used for motility to capture prey
- prey is phagocytosed in vacuole
what are the two ways in which ciliates multiply?
- Binary fission
- macronucleus elongates and divides into 2 macronuclei, each inherited by 2 daughter cells - conjugation
- 2 protozoa establish physical contact and macronucleus disintegrates
- mitosis/meiosis produces 4 daughter cells
- micronuclei degenerate
- exchange of genetic info produces diploid micronuclei that divide by mitosis
what are apicomplexans (parasitic protozoa)?
- spore-forming parasites, lacking flagella, cilia or pseudopods
- contain apical complex to enter host cell
- contain apoplast which degenerates into chloroplast to carry out fatty acid metabolism
- micronemes and rhoptries secrete enzymes for metabolism
how do apicomplexans multiply?
uses a vector for host infection e.g. mosquito
- sporozoite is infectious form
- these multiply by mitosis in schizont ruptures to release merozoites which invade red blood cells
- merozoites form male/female gametocytes which go into mosquito
- in mosquito, gametes fuse to form zygote that invades cells and undergoes meiosis to produce sporozoites
what are dinoflagellates?
- photosynthetic aquatic organisms
- mixotrophs: use sources of energy that aren’t light
- responsible for algae blooms which can be toxic to fish
- mobile predatory algae which feed on bacteria, diatoms, ciliates and other algae
- involved in symbiotic and parasitic interactions
- cell walls made of cellulose plates called thecae, and chloroplasts have complex membranes
what is the life cycle of dinoflagellates?
- vegetative reproduction
- can exist as dormant (cysts)
- little is known about their life cycle
- hypnozygote enables cell to exist as both diploid or haploid
what are parasitic protozoa?
- mobile parasites that cause common diseases in humans e.g. diarrhoea
- mostly harmful, but sometimes symbionts
- can be transmitted via vectors or direct contact between individuals
example: metamonads
what are examples of metamondads?
Mixotricha paradoxa:
- found in gut of termites
- lives in symbiosis with other bacteria
- 1 endosymbiotic bacterium degrades cellulose
- 2 ectosymbiotic bacteria provide motility in form of spirochetes
Giardia lamiblia:
- human parasite causing diarrhoea
- contains 2 nuclei and divides by binary fission
- use adhesive discs to adhere to epithelial cells
Trypanosoma brucei:
- transmitted through a fly
- causes fever, headaches, and can invade the CNS, causing sleep cycle disruption
what are slime molds and amoebas?
- predatory organisms found in damp environments
- differentiate to multicellular reproductive stage when food supply is low
- amoebas cause human diseases via contaminated water
How do pseudopods aid amoeba motility?
- amoeba cell shape is variable
- motility/predation is conferred by pseudopods created by actin polymerisation/diassembly
- actin assembly pushes the membrane to form pseudopods
- same mechanism as human phagocytes
Give an example of a cellular slime mold:
Dictyostelium discodeum:
- grows as an amoeboid, unicellular organism that divides by binary fission
- produces cAMP metabolite when starved that drives aggregation to form slug
- slug differentiates to a fruiting body (sporangium + stalk)
- spores are released to start new cycle
give an example of a plasmodial slime mold:
Physarum polycephalum:
- grows and divides by binary fission as an amoeboid single cell
- individual cells can aggregate to form plasmodium
- single cell and single cytoplasm with several nuclei
- plasmodium forms a fruiting body
- spores are released to initiate a new cycle
