L14 Flashcards
What is a microbiome?
The diverse community of organisms, including bacteria, viruses, fungi, and other microbes, that inhabit a particular environment, such as the human body, plant roots, or seawater.
What is a holobiont?
A host organism and its associated community of symbiotic microorganisms, collectively functioning as a single ecological unit.
Do humans provide a great habitat for microbes?
Yes, for microbes we are just like any other environment
What is mutualism?
Where both partners gain
Is the stability of the human microbiota critical to health?
Yes, diversity and abundance of the microbiome varies with host but also part of the body
What varies between different locations in the GI tract?
Microbiota composition
Why is the small intestine a harsh environment?
Short transit time, excretion of digestive enzymes and bile.
What are the conditions in the colon?
Anaerobic, it is enriched with firmicutes and bacteroidetes, methanogens archaea present.
In what way does microbial diversity in the gut vary?
Colon harbours trillions of bacteria, in exchange bacteria digest complex carbohydrates, boost immune system and fend off pathogens. Oral antibiotics can kill gut microbiome, reducing diversity and functionality.
What types of bacteria are associated with human gut?
Strict anaerobes or facultative aerobes
How is the gut microbiome assembled?
In a stepwise manner, newborns acquire some gut bacteria from their mothers. Quickly displaced and or outnumbered with the infants own bacteria. Increases in richness of bacteria as infants move from milk-based diet to an adult diet.
How do bacteria assemble the gut microbiome?
Firmicutes are the first to colonise, proteobacteria are detected soon after followed by actinobacteria. Once food is introduced, bacteriodetes establish and displace most of the bacteria from other groups expect for the firmicutes.
By what age is a child’s gut microbiome essentially adult like?
By school age, it is dominated by firmicutes and bacteriodetes
As a host ages what increases?
Diversity and stability
What is the difference in gut communities of individuals with obesity, insulin resistance?
Less diverse
What is alteration in the gut microbiome called?
Dysbiosis
As our association with the gut microbiota is mutualistic, what do bacteria get from us?
Gut environment is so good that it does not need to make amino acids, no need for sporulation in firmicutes
As our association with the gut microbiota is mutualistic, what do we get from bacteria?
Firmicutes and bacteriodetes breakdown and ferment complex carbohydrates, and generate formate and short chain fatty acids (SCFAs).
What do firmicutes produce?
SCFA butyrate which is absorbed by the colonic epithelium.
What do bacteriodetes produce?
SCFAs acetate and propionate, distributed by the bloodstream to peripheral organs
How is formate broken into CO2 and H2?
Methanogenic archaea remove hydrogen produced by fermentation carried out by firmicutes and bacteriodetes. Methanogenic archaea use CO2 as last electron acceptor and produce methane as byproduct. CO2 + 4H2 -> CH4 + 2H20
What other bacteria are in the human gut?
Low abundant bacterial phyla - proteobacteria, actinobacteria, verrucomicrobia. Some commensal bacteria, some bacteria opportunistic pathogens. SCFAs if not absorbed by colonic epithelium help drop the pH of intestinal lumen to control growth of harmful bacteria
Summary of SCFAs (butyrate, acetate, propionate)
Promote colonic health, consumed by other microbes, promote general health.
What is fecal matter transplant?
Used to treat a severe bacterial infection, stool from healthy individuals used to restore gut microbiome
What is the rumen microbiome?
SCFAs are also consumed by other microbes in the gut.
What is syntropy and an example?
Interaction where one species feeds off metabolic products of another. E.g. what occurs in gut of ruminants
Where does digestion of plant materials take place? And what environment is it?
Takes place in the rumen, which is an anaerobic environment. Bacteria, fungi, protozoa degrade cellulose and other plant-polymers into sugars, sugars are fermented into fatty acids.
How do bacteria and fungi cooperate in the rumen?
By degrading and fermenting the plant-derived polymers to generate essential nutrients for the host.
What are protists in the rumen involved in?
Cellulose degradation and predate on bacteria.
What do archaea produce?
Methane from hydrogen and CO2.
What increases fermentation rate?
Syntropic removal of H2, more ATP for microbes are produced
What is commensalism?
One partner benefits, while the other is unaffected.
What can commensal benefits include?
Amino acids, benefits, vitamins, and growth. Often host released products are waste products that the commensal organism scavenge.
What do Bacteria do in our mouth? Steps 1-2
Bacteria colonise teeth and build multispecies-biofilms on the enamel dental plaque, first colonisers are streptococci and actinomycetes. Commensal bacteria form a biofilm that feeds on food debris that stick to it and establish mutualistic interactions and feed one another.
What do Bacteria do in our mouth? Steps 3 - 5
If biofilm is left to grow pathogenic bacteria join the biofilm, pathogens grow leading to cavity formation and gum inflammation. S. Mutans ferments sugar and secretes acids. Excessive sugar allows S. mutans to produce more acid eroding enamel causing cavities. P. gingivalis can invade the gum epithelium inflammation and gum disease.
What is parasitism?
Pathogenic bacteria that cause infectious diseases, pathogenic bacteria gain while host looses.
What three challenges does an infectious agent confront?
Encounter, entry, establishment
What happens in the encounter stage?
The host and infecting agent must meet. The source of the infecting agent may be the environment.
What happens in the entry stage?
This can occur with or without penetration
What is the establishment phase?
Overcoming the hosts defences, outcome of interactions between host and pathogen determines whether there will be symptoms of disease.
What factors does establishment of disease depend on?
Inoculum size, virulence, host defences
What are bacterial toxins?
Microbes that can cause disease by secretin toxins
What can GI diseases be caused by?
Microbes secreting toxins
What is vibrio cholerae?
Motile gram-negative bacteria that inhabits lakes, rivers, etc. Most of the strains rarely cause disease. It can swim freely or form biofilms on small crustaceans.
What makes vibrio cholerae so pathogenic?
Pathogenic strains contain pathogenicity islands, regions that encode cholera toxin (CT), toxin-coregulated-pilus (TCP). CT coded by part of the genome of a fikamentous phage
How do vibrio cholerae transfer pathogenicity?
Transfer pathogenicity islands to other vibrios via transformation or transduction. CTX phages carry the pathogenicity islands, phage gets inserted into V. cholera genome. V. cholera genome now has the ability to produce CT and TCP. TCP mediates bacterial aggregation and helps V. cholerae colonise the intestine lining. LPS are the out membrane of vibrios and determine if they are resistant to phages.
What does the cholera toxin induce?
Efflux of water into the lumen of the intestine, which causes watery diarrhea.
What role does adenylyl cyclase play with vibrio cholerae?
Continuous activation of adenylate cyclase fills cells with cAMP and chlorine is pumped into the lumen. Water follows the direction of the Cl- gradient.
Has Cyanobacteria and plant symbiosis evolved?
Yes
How doe aliivibrio fischeri and squid have a symbiotic relationship?
Squid provides nutrients for bacteria, bacteria provides luminescence protecting squid from predators.
