Gram Positive Bacteria Flashcards
Describe the gram positive bacteria cell wall.
- it has a thick peptidoglycan cell wall
- no outer membrane
What are the three groups of gram positive bacteria?
- Firmicutes : endospore forming (Bacillus), Nonsporulating (Staphlyococcus)
- Mollicutes : no peptidoglycan cell wall (Mycoplasma)
- Actinobacteria : Mycobacterium, filamentous (Streptomyces)
Explain the situation with spore forming bacilli (Firmicutes)
L> shape of them?
L> what is the f(x) of the spores?
- gram positive RODS (their shape) hence why they are called BACILLI
- they produce endospores: highly differentiated cells which arise by asymmetric division
- These spores aid in survival bc they are highly resistant to heat, chemicals, radiation and dehydration. It is a dormant stage that can last for years.
- Dispersal: wind, water and animal gut
What is the difference between spore formation in bacteria and fungi?
- fungi form spores via sexual reproduction and therefore separate these from endospores…they are NEVER formed this way
Describe Bacillus anthracis. L> what does it cause L> stats? L> grows where? L> What can it potentially be used as?
- causes anthrax
- 80% mortality when untreated
- grows in lymph nodes and lymphatic tissue of lungs
- death from septicaemia. haemorrhagic meningitis
- potential bioagent in biowarfare
L> it is very treatable via common antibodies.
The universal evolutionary tree is based on what?
- rRNA sequence
- three domains: Eubacteria, Archaea and Eukaryotes
Anthrax poisoning is very common with whom?
- people that work with animal hides via cuts. The toxins taken in via respiratory are very different symptoms and are more toxic this way= untreatable. The spores are what make Bacillus anthracis a potential bioweapon
Lifecycle of an endospore forming bacterium?
- Vegetative cell –> Sporulating cell (veg cell has a developing spore inside it) –> mature spore breaks off from the cell –> germination occurs and you have a new vegetative cell.
- poor conditions are when spore formation occurs and favourable conditions will bring the spore into germination….the spore protects DNA
Describe the endospore structure.
L> simple or complex?
L>contains what acid complexed with what ion?
L> core?
- it is complex with many layers
- contains dipicolinic acid complexed with Ca 2+
L> dehydrates endospore and stabilizes DNA (resistant to UV) - core contains small acid soluble proteins (SASP)
L>Bind DNA- protection from damage..less sensitive to UV damage and important as a nutrient source once germ occurs.
L>Carbon and energy source for germination
Describe the two scenarios division in endospore forming bacterium depending on good or bad conditions.
- Binary fission (Good conditions) - Replication of genome occurs and the cell is split in half.
- Sporulation (Bad Conditions) - chromosomes are distributed along the entire cell for division–(asymmetric division)–>Full copy of genome will be in the forespore (tip of mother cell). The forespore gets engulfed in the mother cell. Spore forms (other cell dies) and it goes into a dormant stage…good conditions will bring it into germination.
Describe the layers of a bacterial endospore.
- exosporium
- spore coat
- core wall
- cortex
- DNA
Differences between the vegetative cells and endospores?
- calcium content is high in endospore not in veg cell
- dipicolinic acid is absent in veg cell but present in endospore
- enzyme activity is high in veg cell but low in endospore
- metabolism is high in veg cell but is low or absent in endospore
- mRNA is present in veg cell but low or absent in endospore
- radiation resistant present in endospore but not veg
- high water content in veg cell (80-90%) and low in endospore core (10-25%)
- SASP is absent in veg but present in endo
Discuss the parasporal body in Bacillus thuringiensis.
- it is toxic to insect larvae not humans.
- it is converted to something toxic in the gut of the insect…secondary metabolite
- insect resistant GM crops?
Give an example of nonsporulating Gram Positive Bacteria.
- Staphylococcus L> aerobic, cocci L> resistant to reduced water potential L> tolerate high salt L> many species are pigmented L> staphylococcus aureus (yellow) L> methicillin resistant staphylococcus aureus (MRSA)
What group of gram positive bacteria have no cell walls?
L> compensation?
- Mycoplasma
L> no cell wall visible by EM
L> key components of peptidoglycan are absent (hence odd shape of bacterium)
L> membranes contain sterols and lipoglycans which stabilize the membrane
Mycoplasma cells are considered what?
- pleomorphic
L> cells may be cocci or filaments of various lengths - some of the smallest organisms capable of autonomous growth
Mycoplasmas:
- describe them
- example?
- some of the smallest organisms capable of autonomous growth - smallest genome
- parasites that inhabit animal and plant hosts
- often defective in several biosynthetic pathways bc they are parasites obv
- Mycoplasma genitalium: Host associated, genome 580kbp and 470 ORFs
Actinobacteria: Mycobacterium
L> describe them
L> example?
- rod shaped organisms, can be somewhat pleomorphic
- obligate aerobe
- facultative intracellular parasite (can live within macrophages)
- complex cell wall
- Mycobacterium tuberculosis : cause of TB..discovered by Robert Koch
- some grow very slowly…TB has a gen time of 15-20 hours (ecoli = 20min) but this allows them to go un noticed by the host immune system
Describe the structure of the Mycobacterial cell wall.
- gram positive even though it doesn’t stain as one
- Plasma Membrane
- Peptidoglycan
- Arabinogalactin
- Mycolic Acids
Filamentous Actinomycetes: Streptomyces.
L> Brief description of it’s biology; what is it very similar to growth wise?
- filamentous, gram positive bacteria
- branching filaments: produce mycelium analogous to mycelium of filamentous fungi
- Produce spores called conidia (asexually)
- important secondary metabolites
- strict aerobes that produce many extracellular enzymes (important in breaking down plant cell walls)
- genomes are typically large
Streptomyces:
-Ecology?
- primary soil microorganism
- over 500 species
- abundant and important in soil
L> major role in the cycling of carbon trapped in insoluble organic debris
L> produce many and diverse hydrolytic exoenzymes
L> 7 cellulases and 5 chitinases
Explain Streptomyces coelicolor life cycle.
-vegetative hyphae emerge from germinating spore
- mycelial growth: tip extension gives filaments, few cell walls, many copies of the genome in each cell, elongate and branch on the surface and penetrate the medium
- Nutrient depletion results in a switch to growth of aerial hyphae
L> complex signalling cascade, production of a surfactant that coats some emerging filaments this allows them to grow away from the substrate, substrate mycelia used as nutrient source
- Once aerial hyphal growth stops synchronous, multiple septation to give rise to prespore compartments (one copy of genome)
- Mature and develop characteristic grey pigment
Describe spore formation in Streptomyces.
- spores produced when colony ages
- aerial filaments (sporophores)
L> Multinucleated, cross walls form, individual cells develop into spores - spores are for survival and dispersal
Describe streptomyces wtr antibiotic production
- secondary metabolites
- 50% of all isolated streptomyces produce antibodies
- over 500 antibodies produced by them
- approx 50 with human, veterinary or industrial applications
- Ex: Aminoglycosides, Tetracyclines
- production is linked to sporulation
- potential survival strategy?? Decrease competition by producing secondary metabolites to continue to grow aerial hyphae via clearing area around it.
Describe some characteristics of conidia?
- formed at end of aerial hyphae
- resistant to dehydration
- dormant but more active than endospores wtr metabolism
- formed by the septation of terminal aerial filaments
- role in dispersal and survival in adverse conditions
