The social microbe II – interactions of microbes and macrobes Flashcards
List some microbial interactions
- hosts
- mutualists
- commensals
- symbionts
- pathogens
Describe commensal
- an animal or plant which lives attached to or as a tenant of another, and shares its food
- distinguished from a parasite, which feeds on the body of its host
- also applied to the host itself
Describe symbiosis
association of two different organisms which live attached to each other, or one as a tenant of the other, and contribute to each other’s support.
Define infection
colonisation of the host from an infection source
Define transmissibility
ability to spread from host to host
Define carriage
establishment of a long-term harmless relationship
Define disease
infections that damage the host (pathology)
Define pathogenicity
ability to cause disease
Define virulence
severity of disease caused
Describe soil amoeba
- exhibit all types of interactions with bacteria
- prey on bacteria as a food source
- bacteria can parasitise them,
- pre-adapted to parasitise phagocytes
- have endosymbiotic mutualists
List some intracellular lifestyle
- predator-prey
- parasitism
- mutualism
What are the implications of the intracellular predator-prey lifestyle?
- food web and nutrient cycling
- selective force for bacterial community
- mechanisms of intracellular killing
What are the implications of the intracellular parasitic lifestyle?
- discovery of new pathogens
- identification of new virulence factors
- drinking water safety
- human health
What are the implications of the intracellular mutualistic lifestyle?
- mechanisms of genome reduction and gene transfers
- coadaptation in endosymbiosis
- origin of organelles
Explain diverging host associations
- very large ancient population of free living bacteria undergoes recombinational change
- infection causes host association
- diverges into mutualism and pathogenesis
- forms commensal and pathogen respectively
- forms symbiont and obligate respectively
- forms smaller, younger populations
- limits recombinational exchange
Describe the stages of host adaptation
- free living and extracellular microbe acquires genes by HGT, causes changes within the genome
- forms early stage facultative intracellular microbes; gene loss
- forms advanced stage obligate intracellular microbe
- forms extreme stage obligate intracellular mutualist
- forms organelle
What are the roles of the mycobiont in lichens
- protection of the photobiont
- absorb mineral nutrients.
What are the roles of the prokaryotic photobiont in lichens
- synthesis of organic nutrients
- nitrogen fixation
Describe Rhizobium and Fabaceae
- major source of fixed nitrogen for plants
- species-specific for bacteria and plants
– co-evolution of host and symbiont
Describe the role of the plant in the legume/rhizobium symbiosis
- nutrition
- low oxygen tension (leghaemoglobin)
- protection
Describe the role of the bacterium in the legume/rhizobium association
nitrogen fixation
Describe the formation of Rhizobium root nodules
- recognition and attachment
- invasion
- travel through infection thread
- bacteroid formation
- bacterial and plant growth to form the nodules
Describe the Verminephrobacter symbiosis in earthworms
- almost all earth worms harbour species-specific
endosymbionts - Verminephrobacter
- vertically transmitted
- evolutionary ancient association.
- bacteria live on host waste products.
- beneficial for host reproduction (nutritional advantage)
- reductive evolution of the bacterial genome results in streamlining
Describe the nephridia of an earthworm
- clitellum
- intestine
- septum
- pore to exterior
- nephrostome (intake)
- 1st loop
- 2nd loop
- ampulla
- 3rd loop bladder
Describe the genome evolution of vertically transmitted extracellular symbionts
Describe Verminephrobacter symbionts
- high host fidelity
- vertical transmission
- extracellular lifestyle
- scope for HGT
- different pattern of genome evolution from intracellular symbionts
- two different environments: nephridia and cocoon
Describe free-living microbes
- recombination within and between populations
- few pseudogenes
- few mobile elements
Describe the genetics of Verminephrobacter
- genetic mixing, fluctuating environment
- ongoing uptake and loss of genes
- many mobile elements and genome rearrangements
- accelerated evolutionary rates
- few pseudogenes
- no genome reduction
- continuous genome rearrangements
Describe the genetics of insect endosymbioses
- no genetic mixing, stable environment
- host restriction
- accumulation of pseudogenes
- expansion of mobile elements
- chromosomal rearrangements
- accelerated evolutionary rates and gene loss
- loss of mobile elements
- few pseudogenes
- small and stable genome; AT-bias
Describe aphid symbionts
- Buchnera genus
- e.g. Acyrthosiphon pisum (pea aphid)
- e.g. Schizaphis graminum (wheat aphid)
List some ant symbionts
- Blochmannia floridanus
- Blochmannia pennsylvanicus
List a Tsetse fly symbiont
Wigglesworthia glossinidia brevipalpis
Describe bligate mutualistic insect endosymbionts
- P-symbionts
- restricted to bacteriome
- domesticated by the host
- cannot invade naïve hosts
- dependent on host-based mechanisms for transmission
P-symbionts
primary symbionts
bacteriome
consists of specialised host cells (bacteriocytes)
Describe facultative insect endosymbionts
- S-symbionts
- erratically distributed
- not required for host reproduction
- resemble pathogens
- can colonize uninfected hosts & establish stable, maternally inherited infection
- can confer benefits, including protection against natural enemies
S-symbionts
secondary symbionts
Describe facultative insect endosymbiont pathogen resemblance
invade cells, including reproductive organs
Describe insect endosymbiotic reproductive manipulators
- parasites that spread by increasing host reproduction through females offspring;
- through reproductive incompatibility between infected and uninfected insects
- infected males sterilise uninfected females
- e.g. Wolbachia spp.
Describe Buchnera
- obligate intracellular
endosymbionts of aphids. - without the bacteria the aphids die of starvation
- bacteria are maternally transmitted
– and therefore co-evolve with the aphid
Describe Buchnera phylogeny
- most Buchnera genes have close homologues in the Enteric bacteria
- the distant ancestor of Buchnera was probably somewhat like present day Escherichia coli, that has undergone extensive reductive evolution
Describe the metabolic interdependence of Aphids and Buchnera
- bacteria located in
‘bacteriocytes’ - surrounded by an aphid-derived membrane;
- unculturable
- vertically transmitted via the ovary
bacteriocytes
- specialised insect cells
- aka mycetocytes
Describe the host role in the Aphid-Buchnera symbiosis
supplies energy, carbon, and nitrogen, in the form of glutamine from phloem
Describe the symbiont role in the Aphid-Buchnera symbiosis
production of amino acids, especially tryptophan (12
to 16 copies of trpEG genes).
Describe the long-term co-evolution of Aphid-Buchnera
- mutualistic symbiosis
- probably established 150 to 250Mya
Describe Wolbachia
- large group of intracellular alphaproteobacteria
endosymbionts - restricted to Ecdysozoan species
- essential for survival and reproduction of nematodes: mutualists
- present in ~66% of insects
- infect the germ line
- often manipulate host sex ratios for their own benefit: pathogenic capacity
Who is Wolbachia related to?
- Anaplasma
- Ehrlichia
- Rickettsia
Who does Wolbachia infect?
- terrestrial arthropods
- filarial nematodes
Describe the four reproductive phenotypes of Wolbachia
- feminisation of genetic males
- parthenogenic elimination of males from reproduction
- male killing of infected males
- cytoplasmic incompatibility
Whose genetic males do Wolbachia feminise?
- Hemiptera
- Isopoda
- Lepidoptera
For which groups does Wolbachia do parthenogenic elimination of males from reproduction?
- Acari
- Hymenoptera
- Thysanoptera
For which groups does Wolbachia do male killing of infected males?
- Coleoptera
- Diptera
- Lepidoptera
- Pseudoscorpiones
Describe cytoplasmic incompatibility in Wolbachia
prevents infected males mating with females without the
same Wolbachia
For which groups does Wolbachia do cytoplasmic incompatibility?
- Acari
- Coleoptera
- Diptera
- Hemiptera
- Hymenoptera
- Isopoda
- Lepidoptera
- Orthoptera
Describe the use of Wolbachia for disease vector control
- release of Wolbachia-infected males into wild populations where Wolbachia is absent
- release of females harbouring Wolbachia
- release of Wolbachia wMelPop via females
Describe the release of Wolbachia-infected males into wild populations where Wolbachia is absent
reproductive incompatibility with wild females results
in embryonic death of offspring.
Describe the release of females harbouring Wolbachia
- offspring with Wolbachia have reduced competence as pathogens vectors
- as only females transmit disease, males not used
- Wolbachia spreads via cytoplasmic incompatibility
Describe the release of Wolbachia wMelPop via females
- pathogen blocking and spread via cytoplasmic incompatibility
- reduces insect lifespan, further decreasing pathogen transmission
Describe termite symbioses
- symbiotic associations with hindgut microbiota are essential to utilise complex biopolymers
- flagellates and bacteria occur in the gut of lower termites
- higher termites possess only bacteria
- e.g. spirochetes
complex biopolymer
wood
Describe cellulose and symbioses
- metabolic pathways to utilise cellulose has evolved in many bacterial groups
- form the bases of many symbioses
Describe carbohydrate polymers
- abundant biological molecules
- used for storage or as structural components
Describe cellulose
- linear polymer of glucose
- most common carbohydrate synthesised by plants
- key part in the carbon cycle.
- insoluble crystalline microfibrils: highly resistant to enzymic hydrolysis.
Describe ruminants
- digest cellulose for 9-12 hours
- variety of bacteria convert polymers such as cellulose to glucose and then to fatty acids
Describe the rumen
large (100-150l) fermenter kept at constant temperature
Describe the Hawaiian bobtail squid (Euprymna scolopes)- Vibrio fischeri Symbiosis
- light generated by Vibrio fischeri bacterial symbionts camouflage Hawaiian bobtail squid
- prey animals cannot see the squid’s shadow from below.
- squid mucus attracts many bacterial species of into the light
organ
– ciliated cells create a current that expels most bacteria, and hydrogen peroxide creates an environment that only Vibrio fischeri survive - inside the light organ, Vibrio fischeri is provided with sugars and amino acids
- daily rhythm of alternating symbiont metabolism between glycerol phosphate respiration and chitin fermentation facilitates luminescence
- light organ becomes acidic at night, increasing oxygen availability
- female squid have a second symbiotic organ containing a simple symbiotic community
Describe the holobiont
organisms are an expression of a combination of their genome and their microbiota.
Describe the human microbiota
- dynamic
- major role in health and disease: dysbiosis
Describe the functions of the indigenous microbiota
- catabolism and bioconversion of dietary or host derived compounds can make nutrients more available to the host.
- synthesise important cofactors or bioactive signaling molecules (e.g. amines)
- signaling between the microbiota and the host can trigger alterations in host function (e.g. altered expression of mucus or alteration of the immune response)
